U.S. patent application number 13/204421 was filed with the patent office on 2011-12-01 for illumination device and liquid crystal display device using the same.
This patent application is currently assigned to SHARP KABUSHIKI KAISHA. Invention is credited to Yasutake Furukoshi, Tetsuya Hamada, Keiji Hayashi, Tetsuya Kobayashi, Masanori Nishido, Mari Sugawara, Toshihiro Suzuki, Fumiaki Yamada.
Application Number | 20110292097 13/204421 |
Document ID | / |
Family ID | 32512113 |
Filed Date | 2011-12-01 |
United States Patent
Application |
20110292097 |
Kind Code |
A1 |
Kobayashi; Tetsuya ; et
al. |
December 1, 2011 |
ILLUMINATION DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE USING THE
SAME
Abstract
An illumination device is provided which can reduce a movement
blur and a tailing phenomenon on a motion picture display while a
drop in display brightness is suppressed, and which can suppress
power consumption, can be made small and light, and can prolong the
lifetime, and a liquid crystal display device using the same is
provided. A light source control part of a control circuit
synchronizes a latch pulse signal outputted from a gate driver
control part to a gate driver, and outputs light emission control
signals to respective light source power supply circuits. The
respective light source power supply circuits change emission
states of cold cathode fluorescent lamps to one of a first to a
third emission states on the basis of the inputted light emission
control signals, and illuminate an LCD panel from a rear surface of
a display area. A first stage emission state is a non-lighting
state, a second stage emission state is a maximum lighting state in
which maximum lighting brightness is obtained, and a third emission
state is an intermediate lighting state in which brightness of
about one half of the second stage emission state is obtained.
Inventors: |
Kobayashi; Tetsuya;
(Kawasaki, JP) ; Suzuki; Toshihiro; (Kawasaki,
JP) ; Sugawara; Mari; (Kawasaki, JP) ; Hamada;
Tetsuya; (Kawasaki, JP) ; Hayashi; Keiji;
(Kawasaki, JP) ; Yamada; Fumiaki; (Kawasaki,
JP) ; Furukoshi; Yasutake; (Kawasaki, JP) ;
Nishido; Masanori; (Kawasaki, JP) |
Assignee: |
SHARP KABUSHIKI KAISHA
Osaka
JP
|
Family ID: |
32512113 |
Appl. No.: |
13/204421 |
Filed: |
August 5, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11881380 |
Jul 26, 2007 |
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13204421 |
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|
10696504 |
Oct 29, 2003 |
7277079 |
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11881380 |
|
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10696507 |
Oct 29, 2003 |
7542471 |
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10696504 |
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Current U.S.
Class: |
345/690 ;
345/102 |
Current CPC
Class: |
G02B 6/0046 20130101;
G09G 2360/16 20130101; G09G 2310/024 20130101; G09G 3/342 20130101;
G09G 3/3648 20130101; G09G 2310/061 20130101; G02B 6/0076 20130101;
G09G 2320/0261 20130101; G09G 3/3666 20130101; G09G 2310/0245
20130101; G09G 2320/0646 20130101; G09G 3/3611 20130101; G02F
1/1336 20130101; G09G 2320/0233 20130101; G09G 5/10 20130101; G09G
2320/064 20130101; G02B 6/0078 20130101 |
Class at
Publication: |
345/690 ;
345/102 |
International
Class: |
G09G 3/36 20060101
G09G003/36; G09G 5/10 20060101 G09G005/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2002 |
JP |
2002-314955 |
Mar 10, 2003 |
JP |
2003-063676 |
Mar 31, 2003 |
JP |
2003-093244 |
Claims
1. An illumination device for illuminating a display area of an
active matrix type liquid crystal display device, comprising: at
least one light source capable of changing light emission
brightness; at least one light-emitting area for emitting light
from the light source; and a light source power supply circuit for
switching between a maximum lighting state in which the light
source is supplied with a first current to emit light at a
specified maximum brightness and an intermediate lighting state in
which the light source is supplied with a second current to emit
light at a specified intermediate brightness lower than the maximum
brightness, wherein said first current is greater than said second
current; wherein the light source power supply circuit synchronizes
with one of gate pulses sequentially outputted to plural gate bus
lines formed in the liquid crystal display device and switches
between the maximum lighting state and the intermediate lighting
state, and when a gate pulse is outputted to a gate bus line as a
display start line in the light-emitting area, the light emission
brightness of the light-emitting area becomes the intermediate
lighting state.
2. An illumination device according to claim 1, wherein the
light-emitting area includes a light emission opening to be used
when the display area is illuminated and disposed substantially in
parallel to an extension direction of a gate bus line formed in the
liquid crystal display device.
3. An illumination device according to claim 1, wherein the
intermediate lighting state is set to have a brightness level of
50% or less of a brightness level of the maximum lighting
state.
4. An illumination device according to anyone of claim 1, wherein
an illumination time in the maximum lighting state is a time of 50%
or less of one frame period.
5. An illumination device according to claim 1, further comprising:
a first light source unit including a first light guide plate and a
first light source disposed at an end thereof, for mainly
illuminating a first light-emitting area and supplying part of
light to an adjacent second light-emitting area; and a second light
source unit laminated on the first light source unit and including
a second light guide plate and a second light source disposed at an
end thereof, for mainly illuminating the second light-emitting area
and supplying part of light to the adjacent first light-emitting
area.
6. An illumination device according to claim 1, wherein the light
source power supply circuit includes a brightness adjusting volume
for adjusting brightness of emission light from the light-emitting
area.
7. A liquid crystal display device of an active matrix type,
comprising: an illumination device according to claim 1.
8. An illumination device according to claim 1, wherein the
light-emitting area includes a plurality of the light sources, and
a light source control system that controls currents fed to the
plurality of the light sources, respectively, to switch between the
maximum lighting state in which the light-emitting area is made to
emit light at the maximum brightness and the intermediate lighting
state in which the light-emitting area is made to emit light at the
specified intermediate brightness lower than the maximum
brightness.
9. An illumination device according to claim 8, wherein the light
source control system feeds a current to at least one of the
plurality of the light sources so that the maximum lighting state
occurs at a specified period and a non-lighting state occurs at a
time other than that, and feeds a current to the remaining light
source so that the non-lighting state occurs at a time of the
maximum lighting state and the intermediate lighting state occurs
at a time other than that.
10. An illumination device according to claim 8, wherein the light
source control system feeds a current to at least one of the
plurality of the light sources so that a first intermediate
lighting state lower than the maximum lighting state occurs at a
specified period, and a second intermediate lighting state lower
than the first intermediate lighting state occurs at a time other
than that, and feeds a current to the remaining light source so
that a third intermediate lighting state occurs so as to cause the
illumination area to have the maximum lighting state at a time of
the first intermediate lighting state, and a fourth intermediate
lighting state occurs so as to cause the illumination area to have
the intermediate lighting state at a time of the second
intermediate lighting state.
11. An illumination device according to claim 8, wherein the light
source control system feeds a current to at least one of the
plurality of the light sources so that the intermediate lighting
state always occurs, and feeds a current to the remaining light
source so that the illumination area has the maximum lighting state
at a specified period and has a non-lighting state at a time other
than that.
12. An illumination device according to claim 8, wherein the light
source control system controls a current so that a non-lighting
state occurs between the maximum lighting state and the subsequent
intermediate lighting state.
13. An illumination device according to claim 8, wherein the light
source control system controls a current so that a lighting state
lower than the intermediate lighting state occurs between the
maximum lighting state and the subsequent intermediate lighting
state.
14. A liquid crystal display device of an active matrix type,
comprising: an illumination device according to claim 8.
Description
[0001] This is a divisional of application Ser. No. 11/881,380,
filed Jul. 26, 2007, which is a divisional of application Ser. No.
10/696,504, filed Oct. 29, 2003, now U.S. Pat. No. 7,277,079.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an illumination device for
illuminating a display area of a liquid crystal display device, and
a liquid crystal display device using the same. Particularly, the
invention relates to an illumination device which improves motion
picture blur and a tailing phenomenon at the time of display of
motion pictures, and a liquid crystal display device using the
same.
[0004] 2. Description of the Related Art
[0005] [First Related Art]
[0006] As alternate means of a CRT (Cathode Ray Tube) which is a
conventional typical display device, in recent years, an active
matrix type liquid crystal display device (hereinafter abbreviated
to TFT-LCD) in which a TFT (Thin Film Transistor) or the like is
provided as a switching element at each pixel has gone
mainstream.
[0007] In principle, in the TFT-LCD, gradation data written into
each pixel is held for one frame period (equal to a period of a
vertical synchronization signal Vsync). In such a hold type display
system, when a motion picture is displayed, the display can not
respond to a quick image change, and degradation in picture quality
can occur in which an image blur and a tailing phenomenon are
visually recognized.
[0008] In order to solve this problem, a method is proposed in
which a display period of gradation data of each pixel is limited
to a specific period in one frame period in synchronization with a
vertical synchronization signal Vsync (for example, see
undermentioned patent document 1). Besides, in order to realize the
method, a method is proposed in which an illumination area of an
illumination device, such as a backlight unit, for illuminating an
image display area of a TFT-LCD is divided into plural parts in the
image display area, illumination of the respective divided areas is
sequentially turned on and off, and a display period (illumination
period) of each divided area is limited to a specific period in one
frame period (for example, see patent undermentioned documents 2 to
5).
[0009] [Second Related Art]
[0010] More specifically, a cold cathode fluorescent lamp (CCFL) is
used as a light source of a backlight unit for a conventional
TFT-LCD, and a display area of the LCD is illuminated while the
cold cathode fluorescent lamp is always turned on. When a motion
picture display is carried out while the cold cathode fluorescent
lamp is always in a lightening state, in the case where gradation
data is rewritten in a frame period (period) of, for example, 16.7
ms and the motion picture is displayed, since a response time of a
liquid crystal molecule to a change in electric field intensity is
several tens ms, next gradation data is written before the response
of the liquid crystal molecule is completed, and accordingly, there
occurs a disadvantage that a "blur" is seen to be produced on the
motion picture display.
[0011] Besides, in the TFT-LCD, since data written in a certain
frame is held until the gradation data is rewritten in the next
frame, a display blur called trail vision on the basis of a human
engineer viewpoint is also visually recognized, and therefore,
there is a problem that the degree of the blur of the motion
picture becomes large.
[0012] The above problem is explained in detail in undermentioned
nonpatent document 1 and nonpatent document 2. The nonpatent
document 2 discloses a study to improve the motion picture blur by
turning on and off the cold cathode fluorescent lamp of the
backlight unit.
[0013] However, when the cold cathode fluorescent lamp of the
backlight unit is simply turned on and off, an afterimage of a
former frame remains, and this is visually recognized as a ghost of
a moving body in an image. Especially in the case where a line
segment is moved, a tailing phenomenon is visually recognized in
which the line segment is seen doubly or triply, which causes the
display quality to be remarkably degraded.
[0014] Then, as a countermeasure against the ghost, a scan
backlight system is proposed in which a backlight unit is divided
into plural areas and a light source of each divided area is turned
on and off in synchronization with the writing of gradation data.
In order to realize this, a direct type backlight unit is proposed
in which plural light sources such as fluorescent lamps are
arranged substantially in parallel to a gate bus line (scanning
line), and the light sources are sequentially turned on and off for
a plurality of the respective plural divided areas.
[0015] FIG. 74 shows a section obtained by cutting a direct type
backlight unit, which is used for a conventional TFT-LCD to support
a motion picture display, along a plane orthogonal to a tube axial
direction of a cold cathode fluorescent lamp, and a brightness
distribution of illumination light from the backlight unit. In FIG.
74, a gate bus line (not shown) of a TFT-LCD 1008 is extended in a
direction vertical to a paper plane. Besides, a display start line
of one frame exists at an "upper (top)" side of the left in the
drawing, and a final display line exists at a "lower (bottom)" side
of the right in the drawing. A backlight unit 1000 is divided into
four areas from the "top" to the "bottom" of the drawing. The
respective divided areas are separated by U-shaped lamp reflectors
(reflection plate) 1002, and a cold cathode fluorescent lamp 1004
whose tube axis extends in the extending direction of the gate bus
line is disposed in each of the lamp reflectors. A light emission
port of the backlight unit 1000 is disposed at the rear surface of
a display area of the TFT-LCD 1008 through a transmission diffused
plate 1006.
[0016] [Third Related Art]
[0017] In recent years, the screen of the TFT-LCD 1008 has been
enlarged and its brightness has been intensified, and also in the
backlight unit 1000, there occurs a necessity to improve light
emission brightness by increasing the number of luminous tubes.
[0018] Besides, as compared with a CRT, the TFT-LCD 1008 continues
to output light for one frame, so that an image blur occurs in a
motion picture display, and picture quality performance is inferior
to the CRT of impulse light emission (undermentioned nonpatent
document 3). In order to cope with this, the patent document 1
proposes a method of causing an LCD to perform an impulse
operation, and a technique to realize an impulse operation is
disclosed in undermentioned patent document 2 or patent document 6
in which the backlight unit 1000 is duty (flicker) driven in a unit
of one frame, and in undermentioned patent document 7 in which
image data and black writing are alternately performed. However,
when the duty driving or black writing is merely performed, alight
output time is reduced and the brightness of a display is lowered,
and accordingly, it is necessary to raise the output of the
backlight unit 1000 at the same time.
[0019] [Fourth Related Art]
[0020] Besides, in a scan type or a blinking type surface
illumination device and liquid crystal display device, a cold
cathode fluorescent lamp or an LED is used as a light source, and
for the purpose of improving the quality of motion pictures
(reducing the blur of a contour), duty driving is performed in
which turning on and off a light is repeated at a frequency of 60
Hz.
[0021] [Fifth Related Art]
[0022] FIG. 75 shows a structure of a direct type backlight unit
used for a conventional TFT-LCD to support a motion picture display
when viewed from a display area side. As shown in FIG. 75, a
backlight unit 1000 is divided into four areas from the top to the
bottom of the drawing. Respective divided areas 1010 to 1013 are
separated by lamp reflectors (reflection plates) 1002 (not shown in
FIG. 75) having U-shaped sections. A cold cathode fluorescent lamp
1004 whose tube axis extends in the extending direction of a gate
bus line of a TFT-LCD 1008 (not shown in FIG. 75) is disposed in
each of the lamp reflectors 1002. A light emission port of the
backlight unit 1000 is disposed at the rear surface of a display
area of the TFT-LCD 1008 through a transmission diffused plate
1006. As a scan type illumination device, this direct type is
mainstream.
[0023] FIG. 76 shows a structure of a sidelight type backlight unit
as another scan type illumination device. As shown in FIG. 76,
respective divided areas 1010 to 1013 of a backlight unit 1000
respectively include light guide plates 1020 optically separated
from each other and arranged in a plane. A dot-like light source
such as an LED 1022 is disposed at each of both end faces of each
of the light guide plates 1020 to 1023.
[0024] Incidentally, the documents of the related art are as
follows:
[0025] [Patent Document 1] [0026] JP-A-9-325715
[0027] [Patent Document 2] [0028] JP-A-11-202285
[0029] [Patent Document 3] [0030] JP-A-11-202286
[0031] [Patent Document 4] [0032] JP-A-2000-321551
[0033] [Patent Document 5] [0034] JP-A-2001-125066
[0035] [Patent Document 6] [0036] JP-A-5-303078
[0037] [Patent Document 7] [0038] JP-A-2001-184034
[0039] [Patent Document 8] [0040] JP-A-2000-194312
[0041] [Nonpatent Document 1] [0042] Television Image Information
Engineering Handbook, Ohmsha P70 to 71
[0043] [Nonpatent Document 2] [0044] ASIA Display/IDW'01
P1779-1780, 1781-1782
[0045] [Nonpatent Document 3] [0046] YasuichiroKurita, "Display
System of Hold-Type Display and Picture Quality in Motion Picture
Display", Preprint of First LCD Forum
[0047] [Nonpatent Document 4] [0048] J. Hirakata et al.: "High
Quality TFT-LCD System for Moving Picture", SID 2002 Digest, p.
1284-1287 (2002)
[0049] [Nonpatent Document 5] [0050] D. Sasaki et al.: "Motion
Picture Simulation for Designing High-Picture-Quality Hold-Type
Displays", SID 2002 Digest, p. 926-929 (2002)
[0051] [Nonpatent Document 6] [0052] K. Sekiya et al.: "Eye-Trace
Integration Effect on The Perception of Moving Pictures and A New
Possibility for Reducing Blur on Hold-Type Displays", SID 2002
Digest, p. 930-933 (2002)
[0053] [Nonpatent Document 7] [0054] H. Ohtsuki et al.: "18. 1-inch
XGA TFT-LCD with Wide Color Reproduction using High Power
LED-Backlighting", SID 2002 Digest, p. 1154-1157 (2002)
[0055] [Nonpatent Document 8] [0056] Gerald Harbers, and two
others, "LED Backlighting for LCD-HDTV, [online], Internet <URL:
http://www.lumileds.com/pdfs/techpaperspres/IDMC_Paper.pdf>
[0057] [Problem of First Related Art]
[0058] In the case of the first related art, when the illumination
light source is simply turned on and off, the display brightness is
remarkably lowered, and there arises a problem that the LCD has low
brightness and low picture quality. For example, in the case where
the display area is divided into five divided areas, and
illumination of 20% is sequentially performed in one frame, in the
one frame period, the brightness becomes 1/5 as compared with the
time of illumination of 100%. On the other hand, when a lighting
time in each divided area is made long, although the brightness is
raised, there arises a problem that degradation of picture quality
such as motion blur becomes remarkable.
[0059] [Problem of Second Related Art]
[0060] In the direct type backlight unit 1000 of the second related
art explained by using FIG. 74, since the cold cathode fluorescent
lamp 1004 is disposed to be close to the rear surface of the
TFT-LCD 1000, as shown in the upper stage of FIG. 74, there is a
defect that uneven brightness is apt to occur. The horizontal axis
of the upper stage of FIG. 74 indicates the position of the TFT-LCD
1008 on the rear surface of the display area, and the vertical axis
indicates the brightness. In the direct type backlight unit 1000,
as indicated by a brightness distribution curved line of the upper
stage of FIG. 74, a difference in brightness is apt to occur
between a place just above the cold cathode fluorescent lamp 1004
and a boundary of the adjacent cold cathode fluorescent lamps 1004,
and there is a defect that uneven brightness is apt to occur by
this. As a method of causing the difference in brightness to be
inconspicuous, a method has been adopted in which a gap between the
transmission diffused plate 1006 and the TFT-LCD 1008 is widened to
diffuse and mix the illumination light, or a method has been
adopted in which the degree of diffusion of the transmission
diffused plate 1006 is raised to further diffuse and uniform the
light emitted to a space just above the cold cathode fluorescent
lamp 1004. However, the former has a problem that the thickness of
the device is increased, and the latter has a problem that the
diffused light is again incident on the cold cathode fluorescent
lamp and is absorbed, and the light quantity is lowered.
[0061] [Problem of Third Related Art]
[0062] When the light emission brightness of the cold cathode
fluorescent lamp 1004 of the backlight unit 1000 is raised to
increase the brightness as in the third related art, there arises a
problem that power consumption and cost are increased. Further,
even in the case where an image having a low average brightness on
a screen is displayed, the light emission brightness of the cold
cathode fluorescent lamp 1004 remains high, and accordingly, the
temperature of the TFT-LCD 1008 rises. It is also necessary to
improve the cooling structure for suppressing this temperature
rise, and according to circumstances, there arises a problem that
the device volume of the TFT-LCD 1008 is increased.
[0063] [Problem of Fourth Related Art]
[0064] In the cold cathode fluorescent lamp or the LED, since
current fed to cause light emission or power supply is restricted,
there is a problem that the brightness can not be made high by the
duty driving. That is, in order to increase the supplied current, a
stabilizer of the cold cathode fluorescent lamp becomes large.
Thus, the stabilizer becomes heavy and thick, and further its cost
becomes high. Furthermore, there is a problem that with the
increase of the current, the driving voltage becomes high, so that
the current-to-light conversion efficiency of the cold cathode
fluorescent lamp is lowered, and the lifetime becomes short.
Besides, for example, in a display device of a portable electronic
equipment such as a notebook computer, strict restrictions are
imposed on the power supply. Also in a solid emission type light
source such as an LED, there arises a problem that the
current-to-light conversion efficiency is lowered by the current
increase, and the lifetime becomes short.
[0065] [Problem of Fifth Related Art]
[0066] In the direct type backlight unit 1000 of the fifth related
art described by use of FIG. 5, since the cold cathode fluorescent
lamp 1004 is disposed to be close to the rear surface of the
TFT-LCD 1008, there is a defect that the brightness distribution is
apt to become irregular, and the uneven brightness on the display
is apt to occur.
[0067] Besides, in the sidelight type backlight unit 1000 of the
fourth related art described by use of FIG. 76, since a light
source, such as the cold cathode fluorescent lamp 1004, having a
relatively large light emission quantity and a long length can not
be used, there is a problem that the brightness is low.
SUMMARY OF THE INVENTION
[0068] An object of the invention is to provide an illumination
device which can reduce a movement blur and a tailing phenomenon on
a motion picture display while a drop in display brightness is
suppressed, and a liquid crystal display device using the same.
[0069] Besides, another object of the invention is to provide an
illumination device which can suppress power consumption, can be
made small and light, and can prolong the lifetime, and a liquid
crystal display device using the same.
[0070] The above objects can be achieved by an illumination device
for illuminating a display area of an active matrix type liquid
crystal display device, which is characterized by comprising at
least one light source capable of changing light emission
brightness, at least one light-emitting area for emitting light
from the light source, and a light source control system for
switching between a maximum lighting state in which the
light-emitting area is made to emit light at a specified maximum
brightness and an intermediate lighting state in which the
light-emitting area is made to emit light at a specified
intermediate brightness lower than the maximum brightness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0071] FIG. 1 is a view showing a rough structure of an
illumination device according to a first embodiment of the
invention and a liquid crystal display device using the same;
[0072] FIG. 2 is a view showing output timings of gate pulses GP
outputted to respective gate bus lines 6 from a gate driver 12 in
synchronization with the input of a latch pulse signal LP, and
light emission brightnesses B(25) to B(28) of respective
light-emitting areas 25 to 28 in the illumination device according
to the first embodiment of the invention and the liquid crystal
display device using the same;
[0073] FIG. 3 is view showing, as subjective evaluations by plural
observers, display quality when a motion picture is displayed on a
display area of a TFT-LCD 1 shown in FIG. 1 while an illumination
period at a maximum lighting brightness and a level of an
intermediate brightness are changed in the illumination device
according to the first embodiment of the invention and the liquid
crystal display device using the same;
[0074] FIG. 4 is a view showing a rough structure of an
illumination device according to a second embodiment of the
invention and a liquid crystal display device using the same;
[0075] FIGS. 5A and 5B are views showing the rough structure of the
illumination device according to the second embodiment of the
invention, in which FIG. 5A is a sectional view taken along line
A-A of FIG. 4 and shows a section obtained by cutting the
illumination device (sidelight type backlight unit) 40, which is
used for a TFT-LCD 1 to support a motion picture display according
to this embodiment, along a plane orthogonal to a tube axial
direction of a cold cathode fluorescent lamp, and FIG. 5B shows a
brightness distribution of illumination light from the illumination
device 40 at a rear surface side of a display area of the TFT-LCD
1;
[0076] FIGS. 6A and 6B are views showing a modified example of the
illumination device 40 according to the second embodiment of the
invention and the TFT-LCD 1 using the same;
[0077] FIGS. 7A to 7C are views for explaining another modified
example of the illumination device 40 according to the second
embodiment of the invention, in which FIG. 7A shows an illumination
device 40 in a state where a double-sided reflection member 64 is
disposed in a gap between light guide plates 51 and 52, FIG. 7B is
a view showing the double-sided reflection member 64, and FIG. 7C
is a view showing another double-sided reflection member 64;
[0078] FIGS. 8A and 8B are views for explaining an expression 1 in
the second embodiment of the invention, in which FIG. 8A is an
enlarged view of FIG. 7C, and FIG. 8B is a view showing the course
of light in an end face at the side of the light guide plate
52;
[0079] FIGS. 9A to 9C are views for explaining still another
modified example of the illumination device according to the second
embodiment of the invention and the liquid crystal display device
using the same, in which FIG. 9A is a view showing a rough
structure of an illumination device of this modified example and a
liquid crystal display device using the same, FIG. 9B is a
sectional view taken along line A-A of FIG. 9A and is a view
showing a section obtained by cutting the illumination device
(sidelight type backlight unit) 40, which is used for a TFT-LCD 1
to support a motion picture display according to this embodiment,
along a plane orthogonal to a tube axial direction of a cold
cathode fluorescent lamp, and FIG. 9C is a view showing a
brightness distribution of illumination light from the illumination
device 40 at the rear side of a display area of the TFT-LCD 1;
[0080] FIGS. 10A and 10B are views showing subjective evaluation as
to whether or not a difference in picture quality from the original
image is felt in a case where in a third embodiment of the
invention, a ratio (duty ratio) of a lighting time of a backlight
unit in one frame period is changed, and further, gradation data is
processed and liquid crystal transmissivity is adjusted;
[0081] FIG. 11 is a view showing a rough operation procedure of a
display data conversion circuit 20 of an illumination device
according to the third embodiment of the invention and a liquid
crystal display device using the same;
[0082] FIG. 12 is a flowchart showing calculation of lightness Y
and a procedure of histogram creation in the display data
conversion circuit 20 of the illumination device according to the
third embodiment of the invention and the liquid crystal display
device using the same;
[0083] FIG. 13 is a flowchart showing a procedure of calculating
the number M of pixels occupied by an image in the case where the
image exists in only a part of one frame (screen) in the
illumination device according to the third embodiment of the
invention and the liquid crystal display device using the same;
[0084] FIG. 14 is a flowchart showing a procedure of calculating
threshold lightness Y.alpha. in the illumination device according
to the third embodiment of the invention and the liquid crystal
display device using the same;
[0085] FIG. 15 is a view showing a duty ratio selection lookup
table used for selection of a duty ratio of a light source in the
illumination device according to the third embodiment of the
invention and the liquid crystal display device using the same;
[0086] FIG. 16 is a view showing a signal control value selection
lookup table for determining a control value when processed
gradation data is outputted to plural data bus lines 8, which is
made to correspond to the threshold lightness Y.alpha. in the
illumination device according to the third embodiment of the
invention and the liquid crystal display device using the same;
[0087] FIG. 17 is a view showing an example of duty driving in the
illumination device according to the third embodiment of the
invention and the liquid crystal display device using the same;
[0088] FIG. 18 is a view showing an example in which a sidelight
type backlight unit as the illumination device according to the
third embodiment of the invention is disposed in an LCD panel;
[0089] FIG. 19 is a view showing an example in which cold cathode
fluorescent lamps A and B of the sidelight type backlight unit as
the illumination device according to the third embodiment of the
invention are duty driven;
[0090] FIG. 20 is a view showing, as the illumination device
according to the third embodiment of the invention, a scan type
backlight unit in which cold cathode fluorescent lamps A to F are
disposed at the rear surface of a panel display surface;
[0091] FIG. 21 is a view showing an example in which the cold
cathode fluorescent lamps A to F of the illumination device
according to the third embodiment of the invention are duty
driven;
[0092] FIG. 22 is a view showing an example in which the sidelight
type backlight unit of the illumination device according to the
third embodiment of the invention is disposed in an LCD panel;
[0093] FIG. 23 is a view showing an example in which the cold
cathode fluorescent lamps A to D of the sidelight type backlight
unit of the illumination device according to the third embodiment
of the invention are duty driven;
[0094] FIG. 24 is a view showing an example in which a direct type
backlight unit of the illumination device according to the third
embodiment of the invention is disposed in an LCD panel;
[0095] FIG. 25 is a view showing an example in which cold cathode
fluorescent lamps A to H of the direct type backlight unit of the
illumination device according to the third embodiment of the
invention are duty driven;
[0096] FIG. 26 is a view showing an example in which the direct
type backlight unit of the illumination device according to the
third embodiment of the invention is disposed in an LCD panel;
[0097] FIG. 27 is a view showing an example in which LEDs A to T of
the direct type backlight unit of the illumination device according
to the third embodiment of the invention are duty driven;
[0098] FIG. 28 is a view showing a state in which in a display
device provided with a scan type backlight unit shown in FIG. 1, a
duty ratio is 80%, the first 20% of one frame period is turned off,
and the remaining 80% of the period is totally turned on;
[0099] FIG. 29 is a view showing a duty driving method for solving
a problem of the backlight of FIG. 28 by using the illumination
device according to the third embodiment of the invention;
[0100] FIG. 30 is a view showing a backlight structure according to
example 1 of a fourth embodiment of the invention;
[0101] FIG. 31 is a view showing driving waveforms of a backlight
according to the example 1 of the fourth embodiment of the
invention;
[0102] FIG. 32 is a view showing a backlight structure according to
example 2 of the fourth embodiment of the invention;
[0103] FIG. 33 is a view showing driving waveforms of a backlight
according to the example 2 of the fourth embodiment of the
invention;
[0104] FIG. 34 is a view showing a specific timing chart of the
backlight according to the example 2 of the fourth embodiment of
the invention;
[0105] FIG. 35 is a view showing a specific timing chart of the
backlight according to the example 2 of the fourth embodiment of
the invention;
[0106] FIG. 36 is a view showing a specific timing chart of the
backlight according to the example 2 of the fourth embodiment of
the invention;
[0107] FIG. 37 is a view showing a specific timing chart of a
backlight according to example 3 of the fourth embodiment of the
invention;
[0108] FIG. 38 is a view showing a specific timing chart of the
backlight according to the example 3 of the fourth embodiment of
the invention;
[0109] FIG. 39 is view showing, as subjective evaluations by plural
observers, display quality when motion pictures are displayed on a
display area of a TFT-LCD 1, while a current value (relative value)
in a maximum lighting state S2 is made 10 and intermediate lighting
states S3 and S4 of FIG. 38 are changed in the backlight according
to the example 3 of the fourth embodiment of the invention;
[0110] FIG. 40 is a view showing characteristics of a cold cathode
fluorescent lamp;
[0111] FIGS. 41A and 41B are views showing an effect obtained when
an illumination device according to the fourth embodiment of the
invention and its duty driving method are used;
[0112] FIGS. 42A and 42B are views showing an effect obtained when
the illumination device according to the fourth embodiment of the
invention and its duty driving method are used;
[0113] FIGS. 43A and 43B are views for explaining example 4 of the
illumination device according to the fourth embodiment of the
invention;
[0114] FIG. 44 is a view showing a result obtained when the duty
driving shown in FIG. 37 or 38 is performed for a backlight unit 75
of the example 4 of the illumination device according to the fourth
embodiment of the invention;
[0115] FIGS. 45A and 45B are views showing a conventional direct
type backlight structure and duty driving as a comparative example
of the illumination device according to the fourth embodiment of
the invention;
[0116] FIG. 46 is a view showing the duty driving of the
conventional direct type backlight unit as the comparative example
of the illumination device according to the fourth embodiment of
the invention;
[0117] FIG. 47 is a view showing a backlight unit 75' according to
example 5 of the illumination device of the fourth embodiment of
the invention;
[0118] FIG. 48 is a view showing a backlight unit 130 according to
example 6 of the illumination device of the fourth embodiment of
the invention;
[0119] FIG. 49 is a view showing a backlight structure according to
example 7 of the illumination device of the fourth embodiment of
the invention;
[0120] FIG. 50 is a view showing current dependency of light
emission efficiency of an LED;
[0121] FIG. 51 is a view showing current dependency of light
emission quantity of an LED;
[0122] FIG. 52 is a view showing a basic structure of an
illumination device according to a fifth embodiment of the
invention;
[0123] FIG. 53 is a view for explaining a first principle of a
light extraction element of the illumination device according to
the fifth embodiment of the invention;
[0124] FIG. 54 is a view for explaining a second principle of a
light extraction element of the illumination device according to
the fifth embodiment of the invention;
[0125] FIG. 55 is a view for explaining a third principle of a
light extraction element of the illumination device according to
the fifth embodiment of the invention;
[0126] FIG. 56 is a view for explaining a fourth principle of a
light extraction element of the illumination device according to
the fifth embodiment of the invention;
[0127] FIG. 57 is a block diagram showing a rough structure of a
liquid crystal display device according to example 5-1 of the fifth
embodiment of the invention;
[0128] FIG. 58 is a view showing a sectional structure of the
liquid crystal display device according to the example 5-1 of the
fifth embodiment of the invention;
[0129] FIG. 59 is a view showing a sectional structure of a
backlight unit 130 of the illumination device according to the
example 5-1 of the fifth embodiment of the invention;
[0130] FIG. 60 is view showing a driving method of the illumination
device according to the example 5-1 of the fifth embodiment of the
invention and a liquid crystal display device using the same;
[0131] FIG. 61 is a block diagram showing a modified example of the
structure of the liquid crystal display device according to the
example 5-1 of the fifth embodiment of the invention;
[0132] FIG. 62 is a view showing a sectional structure of an
illumination device according to example 5-2 of the fifth
embodiment of the invention;
[0133] FIG. 63 is a view showing a sectional structure of an
illumination device according to example 5-3 of the fifth
embodiment of the invention;
[0134] FIG. 64 is a view showing a sectional structure of an
illumination device according to example 5-4 of the fifth
embodiment of the invention;
[0135] FIG. 65 is a view showing a sectional structure of an
illumination device according to example 5-5 of the fifth
embodiment of the invention;
[0136] FIG. 66 is a view showing a sectional structure of an
illumination device according to example 5-6 of the fifth
embodiment of the invention;
[0137] FIG. 67 is a view showing a sectional structure of the
illumination device according to the example 5-6 of the fifth
embodiment of the invention;
[0138] FIG. 68 is a view showing the illumination device according
to the example 5-6 of the fifth embodiment of the invention and a
liquid crystal display device using the same;
[0139] FIG. 69 is a view showing a manufacture method of an
illumination device according to a sixth embodiment of the
invention;
[0140] FIG. 70 is a view showing a cut wavelength change of a
polarizing plate absorption axis with respect to a heat treatment
time in the heat treatment of a polarizing plate in the
illumination device according to the sixth embodiment of the
invention;
[0141] FIG. 71 is a view showing a transmissivity characteristic of
the polarizing plate in an absorption axis direction in a case
where the polarizing plate is subjected to heat treatment at
70.degree. C. in the illumination device according to the sixth
embodiment of the invention;
[0142] FIG. 72 is a view showing a shrinkage ratio of the
polarizing plate with respect to the heat treatment time in the
illumination device according to the sixth embodiment of the
invention;
[0143] FIG. 73 is a view showing a relation between a thermal shock
test time and a light guide plate deformation quantity in the
illumination device according to the sixth embodiment of the
invention;
[0144] FIG. 74 is a view showing a section obtained by cutting a
conventional direct type backlight unit, which is used for a
TFT-LCD to support a motion picture display, along a plane
orthogonal to a tube axial direction, and a brightness distribution
of illumination light from the backlight unit;
[0145] FIG. 75 is a view showing a structure of the conventional
direct type backlight unit, which is used for the TFT-LCD to
support the motion picture display, viewed from the side of a
display area;
[0146] FIG. 76 is a view showing a structure of a sidelight type
backlight unit as another conventional scan type illumination
device;
[0147] FIG. 77 is a schematic sectional view showing a main part of
example 7-1 of a seventh embodiment of the invention;
[0148] FIG. 78 is a circuit diagram showing a structure of a black
display control part in a timing controller of the example 7-1 of
the seventh embodiment of the invention;
[0149] FIG. 79 is a timing chart showing an operation of the
example 7-1 of the seventh embodiment of the invention;
[0150] FIG. 80 is a schematic sectional view showing a main part of
example 7-2 of the seventh embodiment of the invention;
[0151] FIG. 81 is a circuit diagram showing a structure of a black
display control part in a timing controller of the example 7-2 of
the seventh embodiment of the invention;
[0152] FIG. 82 is a schematic sectional view showing a main part of
example 7-3 of the seventh embodiment of the invention;
[0153] FIG. 83 is a circuit diagram showing a structure of a black
display control part in a timing controller of the example 7-3 of
the seventh embodiment of the invention;
[0154] FIG. 84 is a schematic sectional view showing a main part of
an example of a conventional liquid crystal display device; and
[0155] FIG. 85 is a timing chart showing an operation of the
conventional liquid crystal display device shown in FIG. 84.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0156] An illumination device according to a first embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 1 to 3. First, the rough
structure of the illumination device according to this embodiment
and the liquid crystal display device using the same will be
described with reference to FIG. 1. FIG. 1 shows a schematic state
in which a TFT-LCD 1 as an example of the display device is viewed
from the side of a panel display surface. In an LCD panel 2, a
liquid crystal 1c is sealed between two glass substrates, that is,
an array substrate (not shown) on which TFTs 4 are formed and an
opposite substrate (not shown) on which common electrodes Ce are
formed. In the illustrated LCD panel 2, an equivalent circuit of
one pixel is shown. On the array substrate, for example, plural
gate bus lines 6 extending in the horizontal direction of the
drawing are formed in parallel with each other in the vertical
direction. Plural data bus lines 8 extending in the vertical
direction of the drawing are formed in parallel with each other in
the horizontal direction through a not-shown insulating film. Each
of plural matrix-shaped areas defined by the gate bus lines 6 and
the data bus lines 8 formed in the horizontal and vertical
directions as stated above forms a pixel area. A pixel electrode 10
is formed in each pixel area.
[0157] A TFT 4 is formed in the vicinity of an intersection between
the gate bus line 6 and the data bus line 8 in each pixel area, a
gate electrode G of the TFT 4 is connected to the gate bus line 6,
and a drain electrode D is connected to the data bus line 8.
Besides, a source electrode S is connected to the pixel electrode
10. The gate bus line 6 is driven by a gate driver 12, and the data
bus line 6 is driven by a data driver 14. Gradation voltages
(gradation data) are outputted from the data driver 14 to the
respective data bus lines 8, and when a gate signal (gate pulse) is
outputted to any one of the gate bus lines 6, a series of TFTs 4
whose gate electrodes G are connected to the gate bus line 6 are
turned on. The gradation voltages are applied to the pixel
electrodes 10 connected to the source electrodes S of those TFTs 4,
and the liquid crystals 1c are driven between the pixel electrodes
and the common electrodes Ce formed at the opposite substrates.
Besides, in each pixel, a liquid crystal capacitance C1c is formed
of the pixel electrode 10, the common electrode Ce and the liquid
crystal 1c, and a storage capacitance Cs is also formed in parallel
with the liquid crystal capacity C1c.
[0158] The TFT-LCD 1 is provided with a control circuit 16 to which
a clock CLK, a data enable signal Enab and a gradation data Data,
which are outputted from a system side such as a PC (Personal
Computer), are inputted.
[0159] The gate driver 12 includes, for example, a shift driver,
receives a latch pulse signal LP from a gate driver control part 18
in the control circuit 16, and sequentially outputs a gate pulse
from a display start line to perform line sequential driving.
[0160] Besides, the control circuit 16 includes a display data
conversion circuit 20. The display data conversion circuit 20 has
such a function that for example, gradation data Data to be
displayed is compared with previous gradation data Data, and when a
data value is changed to exceed a specified threshold, the
gradation data Data to be displayed is subjected to a specified
weighting processing, and the output gradation data is outputted to
the data driver 14.
[0161] Further, the control circuit 16 includes a light source
control part 22 which controls an illumination device 24 for
illuminating an image display area of the LCD panel 2. The
illumination device 24 of this example uses, as an example, a
direct type backlight unit. The direct type backlight unit of this
embodiment includes plural (four in this example) divided
light-emitting areas 25 to 28, and is disposed so that the LCD
panel 2 can be illuminated from the rear surface of the display
area. When the number of gate bus lines in one frame is L, the
first light-emitting area 25 has an illumination range from the
first gate bus line 6 as the display start line to the (L/4)-th
gate bus line 6. Similarly, the second light-emitting area 26 has
an illumination range from the (L/4+1)-th gate bus line 6 to the
(2L/4)-th gate bus line 6, the third light-emitting area 27 has an
illumination range from the (2L/4+1)-th gate bus line 6 to the
(3L/4)-th gate bus line 6 and the fourth light-emitting area 28 has
an illumination range from the (3L/4+1)-th gate bus line 6 to the
L-th gate bus line 6.
[0162] Each of the light-emitting areas 25 to 28 has such a
structure that a light emission opening which is substantially
parallel to an extension direction of the gate bus line 6 is formed
at a rear surface side of the LCD panel 2, and a portion other than
that is surrounded by a reflection plate or the like. In areas
surrounded by the reflection plates of the respective
light-emitting areas 25 to 28, for example, rod-shaped cold cathode
fluorescent lamps 30 to 33, whose light emission brightness can be
changed by controlling a supplied current, are respectively
disposed while the tube axial direction is made substantially
parallel to the extension direction of the gate bus line 6.
Specified driving currents are fed to the respective cold cathode
fluorescent lamps 30 to 33 from light source power supply circuits
35 to 38. The light source power supply circuits 35 to 38 can give
at least three stage emission states to each of the cold cathode
fluorescent lamps 30 to 33 on the basis of current control signals
from the light source control part 22 of the control circuit 16.
Here, a first stage emission state is a non-lighting state S1, a
second stage emission state is a maximum lighting state S2 in which
the maximum lighting brightness is obtained, and a third stage
emission state is an intermediate lighting state S3 in which about
one half of the brightness of the second stage emission state is
obtained. Incidentally, the maximum lighting brightness does not
necessarily mean the maximum brightness on specifications, which
can be produced by the cold cathode fluorescent lamps 30 to 33, and
also includes the highest brightness in the brightness ranges
adjusted by the light source power supply circuits 35 to 38. A
light source control system is constituted by at least the light
source control part 22 and the light source power supply circuits
35 to 38.
[0163] The light source control part 22 of the control circuit 16
outputs the light emission control signal to each of the light
source power supply circuits 35 to 38 in synchronization with the
latch pulse signal LP outputted to the gate driver 12 from the gate
driver control part 18. Each of the light source power supply
circuits 35 to 38 changes the emission state of each of the cold
cathode fluorescent lamps 30 to 33 to any one of the emission
states S1 to S3 on the basis of the inputted light emission control
signal and illuminates the LCD panel 2 from the rear surface of the
display area.
[0164] FIG. 2 shows output timings of the gate pulses GP outputted
to the respective gate bus lines 6 from the gate driver 12 in
synchronization with the input of the latch pulse signal LP, and
light emission brightnesses B(25) to B(28) of the respective
light-emitting areas 25 to 28. The horizontal direction indicates
time. Here, it is assumed that as described above, the L gate bus
lines 6 exist in the display area and are denoted by line numbers
GL(1), GL (2), . . . , GL (L-1), GL(L) in sequence from the display
start line.
[0165] The light source control part 22 synchronizes with the latch
pulse LP for causing the gate pulse GP(1) to be outputted to the
gate bus line GL(1) as the display start line, and outputs the
light emission control signal for controlling the current, which is
to be fed to the cold cathode fluorescent lamp 30, to the light
source power supply circuit 35. By this, the current fed to the
cold cathode fluorescent lamp 30 from the light source power supply
circuit 35 is controlled, and the light emission brightness B(25)
of the light-emitting area 25 becomes the intermediate lighting
state S3 of almost one half of the maximum lighting brightness.
Thereafter, until the latch pulse LP for causing the gate pulse
GP(3L/4+1) to be outputted to the gate bus line GL(3L/4+1) is
outputted, the light emission brightness B(25) of the
light-emitting area 25 is kept at the intermediate lighting state
S3.
[0166] When the latch pulse LP for causing the gate pulse
GP(3L/4+1) to be outputted to the gate bus line GL(3L/4+1) is
outputted, the light source control part 22 synchronizes with it
and outputs a specified light emission control signal to the light
source power supply circuit 35. By this, the current fed to the
cold cathode fluorescent lamp 30 from the light source power supply
circuit 35 is controlled, and the light emission brightness B(25)
of the light-emitting area 25 becomes the maximum lighting state S2
in which the maximum lighting brightness is obtained. Thereafter,
one frame period f is completed, a next frame period f is started,
and until the latch pulse LP for causing the gate pulse GP(1) to be
outputted to the gate bus line GL(1) is outputted, the light
emission brightness B(25) of the light-emitting area 25 is kept at
the maximum lighting state S2. Each time the next frame period f
starts, the above operation is repeated.
[0167] By this illumination operation, the light emission
brightness B(25) of the light-emitting area 25 becomes the maximum
lighting state S2 only in the 1/4 frame period before the end of
the one frame period f, and the area of the 1/4 frame from the top
of the one frame (display area) is illuminated with the maximum
brightness. For the other period of from the start of the one frame
period f to the 3/4 frame point of time, the light emission
brightness B(25) of the light-emitting area 25 is kept at the
intermediate lighting state S3, and the area of the 1/4 frame from
the top of the one frame is illuminated with the intermediate
brightness.
[0168] Next, when attention is paid to the light-emitting area 26,
the light source control part 22 synchronizes with the latch pulse
LP for causing the gate pulse GP(L/4+1) to be outputted to the gate
bus line GL(L/4+1) shifted from the display start line by 1/4
frame, and outputs the light emission control signal for
controlling the current, which is to be fed to the cold cathode
fluorescent lamp 31, to the light source power supply circuit 36.
By this, the current fed from the light source power supply circuit
36 to the cold cathode fluorescent lamp 31 is controlled, and the
light emission brightness B(26) of the light-emitting area 26
becomes the intermediate lighting state S3 of almost one half of
the maximum lighting brightness. Thereafter, until the latch pulse
LP for causing the gate pulse GP(1) to be outputted to the gate bus
line GL(1) is outputted, the light emission brightness B(26) of the
light-emitting area 26 is kept at the intermediate lighting state
S3.
[0169] When the latch pulse LP for causing the gate pulse GP(1) to
be outputted to the gate bus line GL(1) is outputted, the light
source control part 22 synchronizes with it and outputs a specified
light emission control signal to the light source power supply
circuit 36. By this, the current fed from the light source power
supply circuit 36 to the cold cathode fluorescent lamp 31 is
controlled, and the light emission brightness B(26) of the
light-emitting area 26 becomes the maximum lighting state S2 in
which the maximum lighting brightness is obtained. Thereafter,
until the latch pulse LP for causing the gate pulse GL(L/4+1) to be
outputted to the gate bus line GL(L/4+1) is outputted, the light
emission brightness B(26) of the light-emitting area 26 is kept at
the maximum lighting state S2. The above operation is repeated at
the frequency of the frame period f.
[0170] By this illumination operation, the light emission
brightness B(26) of the light-emitting area 26 becomes the maximum
lighting state S2 only for the first 1/4 frame period of the one
frame period f, and only in the period, the area of the 1/4 frame
in the range of 1/4 to 1/2 from the top of the one frame is
illuminated with the maximum brightness. In the period other than
that, the light emission brightness B(26) of the light-emitting
area 26 is kept at the intermediate lighting state S3, and the area
of the 1/4 frame in the range of 1/4 to 1/2 from the top of the one
frame is illuminated with the intermediate brightness.
[0171] Next, when attention is paid to the light-emitting area 27,
the light source control part 22 synchronizes with the latch pulse
LP for causing the gate pulse GP(2L/4+1) to be outputted to the
gate bus line GL(2L/4+1) shifted from the display start line by the
1/2 frame, and outputs the light emission control signal for
controlling the current, which is to be fed to the cold cathode
fluorescent lamp 32, to the light source power supply circuit 37.
By this, the current fed from the light source power supply circuit
37 to the cold cathode fluorescent lamp 32 is controlled, and the
light emission brightness B(27) of the light-emitting area 27
becomes the intermediate lighting state S3 of almost one half of
the maximum lighting brightness. Thereafter, until the latch pulse
for causing the gate pulse GP(L/4+1) to be outputted to the gate
bus line GL(L/4+1) is outputted, the light emission brightness
B(27) of the light-emitting area 27 is kept at the intermediate
lighting state S3.
[0172] When the latch pulse LP for causing the gate pulse GP
(L/4+1) to be outputted to the gate bus line GL(L/4+1) is
outputted, the light source control part 22 synchronizes with it
and outputs a specified light emission control signal to the light
source power supply circuit 37. By this, the current fed from the
light source power supply circuit 37 to the cold cathode
fluorescent lamp 32 is controlled, and light emission brightness
B(27) of the light-emitting area 27 becomes the maximum lighting
state S2 in which the maximum lighting brightness is obtained.
Thereafter, until the latch pulse for causing the gate pulse
GP(2L/4+1) to be outputted to the gate bus line GL (2L/4+1) is
outputted, the light emission brightness B(27) of the
light-emitting area 27 is kept at the maximum lighting state S2.
The above operation is repeated at the frequency of the frame
period f.
[0173] By this illumination operation, the light emission
brightness B(27) of the light-emitting area 27 becomes the maximum
lighting state S2 only in the 1/4 frame period in the range of 1/4
to 1/2 from the head of the one frame period, and only in the
period, the area of the 1/4 frame in the range of 1/2 to 3/4 from
the top of the one frame is illuminated with the maximum
brightness. In the other period, the light emission brightness
B(27) of the light-emitting area 27 is kept at the intermediate
lighting state S3, and the area of the 1/4 in the range of 1/2 to
3/4 from the top of the one frame is illuminated with the
intermediate brightness.
[0174] Similarly, in the light-emitting area 28, the light source
control part 22 synchronizes with the latch pulse LP for causing
the gate pulse GP(3L/4+1) to be outputted to the gate bus line
GL(3L/4+1) shifted from the display start line by the 3/4 frame,
and outputs the light emission control signal for controlling the
current, which is fed to the cold cathode fluorescent lamp 33, to
the light source power supply circuit 38. By this, the current fed
from the light source power supply circuit 38 to the cold cathode
fluorescent lamp 33 is controlled, and the light emission
brightness B(28) of the light-emitting area 28 becomes the
intermediate lighting state S3 of about one half of the maximum
lighting brightness. Thereafter, until the latch pulse LP for
causing the gate pulse GP(2L/4+1) to be outputted to the gate bus
line GL(2L/4+1) is outputted, the light emission brightness B(28)
of the light-emitting area 28 is kept at the intermediate lighting
state S3.
[0175] When the latch pulse LP for causing the gate pulse
GP(2L/4+1) to be outputted to the gate bus line GL(2L/4+1) is
outputted, the light source control part 22 synchronizes with it
and outputs a specified light emission control signal to the light
source power supply circuit 38. By this, the current fed from the
light source power supply circuit 38 to the cold cathode
fluorescent lamp 33 is controlled, and the light emission
brightness B(28) of the light-emitting area 28 becomes the maximum
lighting state S2 in which the maximum lighting brightness is
obtained. Thereafter, until the latch pulse LP for cause the gate
pulse GP(3L/4+1) to be outputted to the gate bus line GL(3L/3+1) is
outputted, the light emission brightness B(28) of the
light-emitting area 28 is kept at the maximum lighting state. The
above operation is repeated at the frequency of the frame period
f.
[0176] By this illumination operation, the light emission
brightness B(28) of the light-emitting area becomes the maximum
lighting state S2 only in the 1/4 frame period in the range of 1/2
to 3/4 of the one frame period f, and only in the period, the
lowest stage area of the 1/4 frame is illuminated with the maximum
brightness. In the other period, the light emission brightness
B(28) of the light-emitting area 28 is kept at the intermediate
lighting state S3, and the lowest stage area of the 1/4 frame is
illuminated with the intermediate brightness.
[0177] By the lighting operation as described above, as shown in
FIG. 2, the illumination is obtained in which the whole display
area is illuminated with the intermediate brightness, and the light
emission brightness of the areas obtained by longitudinally
dividing the display area into four band-shaped areas parallel to
the gate bus line 6 becomes maximum sequentially in time
sequence.
[0178] According to this embodiment, the display to support the
motion picture can be realized while the brightness is sufficiently
suppressed to the brightness of 5/8 (=(1/4)A+3/4.times.(1/2)A A:
maximum lighting brightness) times as the brightness of the
conventional hold type illumination device which is always driven
by the maximum lighting brightness. Besides, since the conventional
scan type illumination device to support the motion picture has the
brightness of 1/4 times as the conventional hold type illumination
device, according to the illumination device of this embodiment,
the display having the high brightness of 2.5 times as the
conventional scan type illumination device can be realized.
[0179] In this embodiment, although the operation example has been
described in which the illumination having the maximum lighting
brightness is performed only in the 1/4 period of the one frame
period f (for example, 16.7 ms), it is also possible to prolong the
illumination period of the maximum lighting brightness, and by
this, a higher brightness can be realized. Besides, in this
embodiment, although the description has been given of the case
where the intermediate brightness in the intermediate lighting
state S3 is set to about one half of the maximum lighting
brightness, it is needless to say that the intermediate level can
be set to a brightness other than that.
[0180] FIG. 3 is a graph showing, as subjective evaluations by
plural observers, display quality when a motion picture is
displayed on the display area of the TFT-LCD 1 shown in FIG. 1
while an illumination period at the maximum lighting brightness and
an intermediate brightness level are changed.
[0181] In FIG. 3, the horizontal axis indicates the ratio (%) of
the maximum lighting state S2 to one frame period f, and the
vertical axis indicates the evaluation according to evaluation
points of stages 1 to 5. The evaluation point 1 indicates a case
where a motion picture blur, a tailing phenomenon and the like on
the motion picture display are "very obstructive", and the
evaluation point 2 indicates a case where those becomes
"obstructive". The evaluation point 3 indicates a case where the
motion picture blur and the like are "annoying but tolerable", the
evaluation 4 indicates a case where "a difference is seen but is
tolerable", and the evaluation point 5 indicates a case where
"picture quality is equivalent to a still picture and is
excellent".
[0182] In the drawing, a straight line (A) connecting circular
marks indicates a case where the bright level of the intermediate
lighting state S3 is the same as the brightness level of the
maximum lighting state S2. Accordingly, irrespective of the ratio
of the maximum lighting state S2 to the one frame period f
(hereinafter abbreviated to the ratio of the maximum lighting state
S2), the illumination with the maximum brightness level is
performed throughout the one frame period f. That is, the display
is equivalent to the hold type driving, and accordingly, the
picture image quality is such that the motion picture blur and the
tailing phenomenon become very obstructive, and the evaluation
point is 1.
[0183] In the drawing, a polygonal line (B) connecting x marks
indicates a case where the brightness level of the intermediate
lighting state S3 is about one half of the brightness level of the
maximum lighting state S2. In this case, when the ratio of the
maximum lighting state S2 is within the range of about 10% to 30%,
the motion picture blur and the tailing phenomenon are hardly
visually recognized and the excellent image quality is obtained,
and accordingly, the evaluation point is 4. When the ratio of the
maximum lighting state exceeds 30%, the evaluation is gradually
lowered, however, the evaluation point 3 is obtained until the
ratio becomes about 50%.
[0184] In the drawing, a polygonal line (C) connecting triangular
marks indicates a case where the brightness level of the
intermediate lighting state S3 is 30% of the brightness level of
the maximum lighting state S2. In this case, when the ratio of the
maximum lighting state S2 is within the range of about 10% to 30%,
the motion picture blur and the tailing phenomenon are hardly
visually recognized and the excellent image quality is obtained,
and accordingly, the evaluation point is close to 5. When the ratio
of the maximum lighting state S2 exceeds 30%, the evaluation is
gradually lowered, however, the evaluation point 3 is obtained
until the ratio becomes about 50%.
[0185] In the drawing, a polygonal line (D) connecting square marks
indicates a case where the brightness level of the intermediate
lighting state S3 is 0 (zero) and a period other than the maximum
lighting state S2 becomes the non-lighting state S1. This is the
same as the illumination method of the conventional scan type LCD.
In this case, when the ratio of the maximum lighting state S2 is
within the range of about 10% to 30%, the motion picture blur and
the tailing phenomenon are hardly visually recognized and the
excellent image quality is obtained, and accordingly, the
evaluation point becomes closer to 5. Besides, when the ratio of
the maximum lighting state S2 exceeds 30%, the evaluation is
gradually lowered, however, the evaluation point of 3 or higher is
obtained until the ratio becomes about 50%.
[0186] From FIG. 3, it is understood that even if the brightness
level of the intermediate lighting state S3 is made about 30% of
the brightness level of the maximum lighting state S2, the display
quality comparable to the conventional scan type LCD indicated by
the polygonal line (D) can be obtained. Further, when the
brightness level of the intermediate lighting state S3 is lower
than about 50% of the brightness level of the maximum lighting
state S2, it is regarded as being within the allowable range.
[0187] Besides, when the illumination time of the maximum lighting
state S2 is 30% or less of the one frame period f, the motion
picture blur and the tailing phenomenon hardly occur, and until the
illumination time increases up to 50%, it is regarded as being
within the allowable range.
[0188] Incidentally, in this embodiment, the pixel is illuminated
with the maximum brightness at the point of time when f/2 to 3f/4
has passed since the gradation data was written into the pixel
electrode 10. This is adopted in view of the response time of a
liquid crystal molecule in the liquid crystal 1c to a change of
electric field, and when a liquid crystal material capable of
responding at high speed is used, it is also possible to illuminate
the pixel with the maximum brightness at the point of time when for
example, f/4 to f/2 has passed since the gradation data was
written.
[0189] As described above, the illumination device 24 of this
embodiment is characterized in that in synchronization with the
output control signal (latch pulse LP) of the gate pulse GP, the
illumination device switches between the maximum lighting state S2
and the intermediate lighting state S3.
[0190] Besides, the illumination device 24 of this embodiment
performs such a control that the gate pulse GP is outputted to the
gate bus line 6, the TFT 4 connected to the gate bus line 6 is
turned on, the gradation data is written into the pixel electrode
10, and in a period when the liquid crystal molecule of the liquid
crystal 1c is performing an inclination operation by this to a
desired inclination angle, the intermediate lighting state S3 is
kept, and when the inclination response of the liquid crystal
molecule is almost completed, the maximum lighting state S2 is made
to occur. By doing so, it is possible to solve the problem of the
conventional scan type LCD in which as the maximum lighting state
S2 becomes short, the picture quality degradation such as the
movement blur can be improved, however, since the period other than
the state S2 is kept at the non-lighting state S1, the brightness
of the display screen becomes low. In the illumination device 24,
even if the time of the maximum lighting state S2 is short, since
the illumination is continued at the specified intermediate
brightness level by the intermediate lighting state S3, it is
possible to lessen the drop of the brightness.
[0191] The picture quality degradation such as the movement blur is
suppressed by using the illumination device 24 because the
illumination method thereof skillfully uses a human engineering
feature that the human eye senses a change with emphasis. That is,
the human eye senses an image at the instant when the intermediate
lighting state S3 is changed to the maximum lighting state S2, and
brands it on the retina. This image recognition operation is
performed every frame, and the visual recognition of the movement
blur and the tailing phenomenon is prevented. On the other hand,
since a human being senses the integration value of incident light
to the retina as the brightness, an average of the light quantity
at the intermediate lighting state S3 and the light quantity at the
maximum lighting state becomes the brightness of the display area
of the TFT-LCD 1.
[0192] By using this embodiment, a liquid crystal display device
having high brightness and less movement blur can be realized with
a simple and thin structure, and the invention can contribute to
the improvement in display quality, the reduction in cost of the
device, and the miniaturization.
[0193] In the above embodiment, although the description has been
given of the scan type illumination device in which one frame is
divided into four parts, the structure and the method of the
embodiment can be applied to any case where one frame is divided
into N parts (N is an integer of 1 or larger). For example, in the
case of N=1, in a period when gradation data is being written into
all pixels of the display area of the LCD panel 2, the whole is
illuminated in the intermediate lighting state S3, and after a
specified liquid crystal response time has passed since the pixel
writing of the final line, the whole is illuminated in the maximum
lighting state S2. The maximum lighting state S2 is realized in,
for example, a vertical blanking period. By doing so, one cold
cathode fluorescent lamp (light source) is used and the TFT-LCD can
be realized in which the motion blur and the tailing phenomenon are
reduced while the drop of brightness is suppressed.
[0194] Besides, in the above embodiment, although the description
has been given of the direct type backlight unit as an example, the
invention is not limited to this, and the structure and method of
this embodiment may be naturally applied to a sidelight type
backlight unit in which a light source is disposed at the end of a
light guide plate.
[0195] Incidentally, the illumination driving method in the
illumination device 24 used in this embodiment may be naturally
applied to a driving method of, for example, an EL (Electro
Luminescence) display device (using an organic EL element or an
inorganic EL element) as a self-luminous plane display device.
Second Embodiment
[0196] An illumination device according to a second embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 4 to 8. First, a rough
structure of the illumination device according to this embodiment
and the liquid crystal display device using the same will be
described with reference to FIGS. 4, 5A and 5B. FIG. 4 shows the
rough structure of the illumination device according to this
embodiment and the liquid crystal display device using the same. A
TFT-LCD 1 shown in FIG. 4 is the same as the TFT-LCD 1 of the first
embodiment explained by use of FIG. 1, and structural elements
having the same operation and function are denoted by the same
symbols, and the description will be omitted. FIG. 5A is a
sectional view taken along line A-A of FIG. 4 and shows a section
obtained by cutting an illumination device (sidelight type
backlight unit) 40, which is used for the TFT-LCD 1 to support the
motion picture display according to this embodiment, along a plane
orthogonal to a tube axial direction of a cold cathode fluorescent
lamp. FIG. 5B shows a brightness distribution of illumination light
from the illumination device 40 at the rear surface side of a
display area of the TFT-LCD 1.
[0197] The illumination device 40 of this embodiment is a sidelight
type backlight unit which has a structure for emitting internally
guided light to the outside and in which cold cathode fluorescent
lamps are disposed along the end of a light guide plate. The
sidelight type backlight unit of this example includes plural (four
in this example) divided light-emitting areas 41 to 43, and is
disposed so that an LCD panel 2 can be illuminated from the rear
surface of the display area.
[0198] When the number of gate bus lines in one frame is L, the
first light-emitting area 41 has an illumination range of from the
first gate bus line 6 as the display start line to the (L/4)-th
gate bus line 6. Similarly, the second light-emitting area 42 has
an illumination range of from the (L/4+1)-th gate bus line 6 to the
(2L/4)-th gate bus line 6, the third light-emitting area 43 has an
illumination range of from the (2L/4+1)-th gate bus line 6 to the
(3L/4)-th gate bus line 6 and the fourth light-emitting area 44 has
an illumination range of from the (3L/4+1)-th gate bus line 6 to
the L-th gate bus line 6.
[0199] As shown in FIG. 5A, two light guide plates 51 and 52 are
disposed on substantially the same plane at the side facing the
rear surface of the TFT-LCD 1. The light guide plate 51 is disposed
in the first and the second light-emitting areas 41 and 42, and the
light guide plate 52 is disposed in the third and the fourth
light-emitting areas 43 and 44. A cold cathode fluorescent lamp 46
is disposed at an end of the light guide plate 51 opposite to an
end facing the light guide plate 52, and a cold cathode fluorescent
lamp 47 is disposed at an end of the light guide plate 52 opposite
to an end facing the light guide plate 51.
[0200] Besides, a light guide plate 50 is disposed in the first
light-emitting area 41 and to be adjacent to a surface of the light
guide plate 51 at the side opposite to the side of the TFT-LCD 1. A
cold cathode fluorescent lamp 45 is disposed at one end of the
light guide plate 50. A light guide plate 53 is disposed in the
fourth light-emitting area 44 and to be adjacent to a surface of
the light guide plate 52 at the side opposite to the side of the
TFT-LCD 1. A cold cathode fluorescent lamp 48 is disposed at an end
of the light guide plate 53. The cold cathode fluorescent lamps 45
to 48 are formed into, for example, linear rod shapes. Besides, the
light emission brightnesses of the cold cathode fluorescent lamps
45 to 48 can be changed by controlling the supplied current.
[0201] Specified driving currents are fed from light source power
supply circuits 35 to 38 to the respective cold cathode fluorescent
lamps 45 to 48. The respective light source power supply circuits
35 to 38 can give at least three stage emission states to the
respective cold cathode fluorescent lamps 45 to 48 on the basis of
current control signals from a light source control part 22 of a
control circuit 16. Here, a first stage emission state is a
non-lighting state S1, a second stage emission state is a maximum
lighting state S2 in which maximum lighting brightness is obtained,
and a third stage emission state is an intermediate lighting state
S3 in which about one half of the brightness of the second stage
emission state is obtained. Here, the maximum lighting brightness
does not necessarily mean the maximum brightness on specifications,
which can be produced by the cold cathode fluorescent lamps 45 to
48, and also includes the highest brightness in the brightness
range adjusted by the light source power supply circuits 35 to
38.
[0202] The illumination device 40 according to this embodiment as
described above is constructed such that a light source unit (50,
45) including the light guide plate (light guiding member) 50 and
the cold cathode fluorescent lamp 45 disposed at the end thereof
and for emitting light from one surface is laminated on a light
source unit (51, 46) including the light guide plate 51 and the
cold cathode fluorescent lamp 46 disposed at the end thereof.
Besides, the illumination device 40 is constructed such that a
light source unit (53, 48) including the light guide plate 53 and
the cold cathode fluorescent lamp 48 disposed at the end thereof
and for emitting light from one surface is laminated on a light
source unit (52, 47) including the light guide plate 52 and the
cold cathode fluorescent lamp 47 disposed at the end thereof.
Further, the illumination device 40 is constructed such that the
light source unit (51, 46) and the light source unit (52, 47) are
disposed on the same plane. Besides, the illumination device 40 is
constructed such that the light source unit (50, 45) and the light
source unit (53, 48) are disposed on the same plane.
[0203] Each of the light-emitting areas 41 to 44 is constructed
such that a light emission opening is formed at the rear side of
the LCD panel 2, and a portion other than that is surrounded by a
diffuse reflection plate 55. A diffusion sheet 60 is disposed
between the rear surface of the TFT-LCD 1 and the light emission
opening of the illumination device 40. As light extraction
structures 56 to 59, for example, light scattering patterns are
printed on the rear surface of the light guide plate 50 in the
first light-emitting area 41, the rear surface of the light guide
plate 51 in the second light-emitting area 42, the rear surface of
the light guide plate 52 in the third light-emitting area 43, and
the rear surface of the light guide plate 53 in the fourth
light-emitting area 44. A light extraction structure is not formed
on the rear surface of the light guide plate 51 in the first
light-emitting area 41 and the rear surface of the light guide
plate 52 in the fourth light-emitting area 44.
[0204] By the arrangement of the light extraction structures 56 and
57, most of the light from the cold cathode fluorescent lamp 45 is
guided through the light guide plate 50 while being scattered by
the light extraction structure 56, and further passes through the
portion of the first light-emitting area 41 of the light guide
plate 51 and is emitted from the first light-emitting area 41. At
this time, part of the light is guided through the light guide
plate 51, is scattered by the light extraction structure 57, and is
emitted from the second light-emitting area 42. Further, part of
the light is guided from the light guide plate 51 to the light
guide plate 52 and the light guide plate 53, is scattered by the
light extraction structures 58 and 59, and is emitted from the
third and the fourth light-emitting areas 43 and 44. That is, most
of the light from the cold cathode fluorescent lamp 45 is used for
the illumination of the first light-emitting area 41, and the
remainder is used for the illumination of the second to the fourth
light-emitting areas 42 to 44.
[0205] Similarly, most of the light from the cold cathode
fluorescent lamp 46 is guided through the light guide plate 51, and
is emitted from the second light-emitting area 42 while being
scattered by the light extraction structure 57. At this time, part
of the light is guided to the light guide plates 50, 52 and 53, is
scattered by the light extraction structures 56, 58 and 59, and is
emitted from the first light-emitting area 41, and the third and
the fourth light-emitting areas 43 and 44. That is, most of the
light from the cold cathode fluorescent lamp 46 is used for the
illumination of the second light-emitting area 42, and the
remainder is used for the illumination of the first light-emitting
area 41, and the third and the fourth light-emitting areas 43 and
44.
[0206] On the other hand, by the arrangement of the light
extraction structures 58 and 59, most of the light from the cold
cathode fluorescent lamp 48 is guided through the light guide plate
53 while being scattered by the light extraction structure 59, and
further passes through the portion of the fourth light-emitting
area 44 of the light guide plate 52 and is emitted from the fourth
light-emitting area 44. At this time, part of the light is guided
through the light guide plate 52, is scattered by the light
extraction structure 58, and is emitted from the third
light-emitting area 43. Further, part of the light is guided from
the light guide plate 52 to the light guide plate 51 and the light
guide plate 50, is scattered by the light extraction structures 57
and 56 and is emitted from the second and the first light-emitting
areas 42 and 41. That is, most of the light from the cold cathode
fluorescent lamp 48 is used for the illumination of the fourth
light-emitting area 44, and the remainder is used for the
illumination of the first to the third light-emitting areas 41 to
43.
[0207] Similarly, most of the light from the cold cathode
fluorescent lamp 47 is guided through the light guide plate 52, and
is emitted from the third light-emitting area 43 while being
scattered by the light extraction structure 58. At this time, part
of the light is guided to the light guide plates 50, 51 and 53, is
scattered by the light extraction structures 56, 57 and 59, and is
emitted from the first light-emitting area 41, the second
light-emitting area 43 and the fourth light-emitting area 44. That
is, most of the light from the cold cathode fluorescent lamp 47 is
used for the illumination of the third light-emitting area 43, and
the remainder is used for the illumination of the first and the
second light-emitting areas 41 and 42, and the fourth
light-emitting area 44.
[0208] The light source control part 22 of the control circuit 16
shown in FIG. 4 synchronizes with the latch pulse signal LP
outputted to the gate driver 12 from the gate driver control part
18 and outputs the light emission control signal to the respective
light source power supply circuits 35 to 38. Each of the light
source power supply circuits 35 to 38 changes the emission state of
each of the cold cathode fluorescent lamps 41 to 44 to any one of
the first to the third emission states S1 to S3, and the LCD panel
2 is illuminated from the rear surface of the display area.
[0209] In the structure as stated above, illumination driving
similar to that of the first embodiment shown in FIG. 2 is
performed. In this embodiment, the light emission brightnesses
B(25) to B(28) of FIG. 2 are read as light emission brightnesses
B(41) to B(44).
[0210] The light source control part 22 synchronizes with the latch
pulse LP for causing the gate pulse GP(1) to be outputted to the
gate bus line GL(1) as the display start line, and outputs the
emission control signal for controlling the current, which is to be
fed to the cold cathode fluorescent lamp 45, to the light source
power supply circuit 35. By this, the current fed from the light
source power supply circuit 35 to the cold cathode fluorescent lamp
45 is controlled, and the light emission brightness B(41) of the
light-emitting area 41 becomes the intermediate lighting state S3
of about one half of the maximum lighting brightness. Thereafter,
until the latch pulse LP for causing the gate pulse GP(3L/4+1) to
be outputted to the gate bus line GL(3L/4+1) is outputted, the
light emission brightness B(41) of the light-emitting area 41 is
kept the intermediate lighting state S3.
[0211] When the latch pulse LP for causing the gate pulse
GP(3L/4+1) to be outputted to the gate bus line GL(3L/4+1) is
outputted, the light source control part 22 synchronizes with it
and outputs a specified light emission control signal to the light
source power supply circuit 35. By this, the current fed from the
light source power supply circuit 35 to the cold cathode
fluorescent lamp 45 is controlled, and the light emission
brightness B(41) of the light-emitting area 41 becomes the maximum
lighting state S2 in which the maximum lighting brightness is
obtained. Thereafter, one frame period f is completed, a next frame
periodef is started, and until the latch pulse LP for causing the
gate pulse GP(1) to be outputted to the gate bus line GL(1) is
outputted, the light emission brightness B(41) of the
light-emitting area 41 is kept the maximum lighting state S2. Each
time the next frame periodef is started, the above operation is
repeated.
[0212] By this illumination operation, the light emission
brightness B(41) of the light-emitting area 41 becomes the maximum
lighting state S2 only in the 1/4 frame period before the end of
the one frame period f, and the area of the 1/4 frame from the top
of the one frame (display area) is illuminated with the maximum
brightness. In the other period from the start of the one frame
periodef to the 3/4 frame point of time, the light emission
brightness B(41) of the light-emitting area 41 is kept the
intermediate lighting state S3, and the area of the 1/4 frame from
the top of the one frame is illuminated with the intermediate
brightness.
[0213] Similarly to the description of the first embodiment, the
emission operations in the light-emitting areas 42, 43 and 44 are
performed, and as shown in FIG. 2, the illumination is obtained in
which the whole display area is illuminated with the intermediate
brightness, and the light emission brightnesses of the areas
obtained by longitudinally dividing the display area into four
band-shaped areas parallel to the gate bus line 6 become maximum
sequentially in time sequence. Although this description has been
given of the example in which the maximum lighting state S2 and the
intermediate lighting state S3 are switched, the same effect can
also be obtained when the maximum lighting state S2 and the
non-lighting state S1 are switched.
[0214] Besides, in this embodiment, although the description has
been given of the structure that the two light guide plates are
laminated, and two such pairs are disposed in the plane, the same
effect can also be obtained when the number of laminated plates is
increased. Besides, in the structure shown in FIG. 5A, when the
light source power supply circuits 35 to 38 and the like are
disposed in recess parts (rear surface of the light-emitting areas
42 and 43) of the backlight, or the cold cathode fluorescent lamps
45 and 48 are disposed therein, the reduction in thickness of the
device and the miniaturization can be realized.
[0215] As stated above, although the illumination device 40
according to this embodiment is of the sidelight type, the light
source unit for mainly illuminating one light-emitting area
supplies part of the light to the other adjacent light-emitting
area, and on the other hand, the light source unit for illuminating
the other light-emitting area supplies part of the light to the one
adjacent light-emitting area, and mutual compensation can be made,
and accordingly, as shown in FIG. 5B, a uniform brightness
distribution a can be realized. Besides, the light source is
disposed at the end face of each light guide member, and lighting
and non-lighting of this light source, or lighting and darkening
thereof are individually controlled, so that the illumination
device of the liquid crystal display device suitable for motion
picture display can be realized to be thin.
[0216] Next, a modified example of the illumination device 40
according to this embodiment and the TFT-LCD 1 using the same will
be described with reference to FIGS. 6A and 6B. The structure shown
in FIG. 6A is the same as the structure shown in FIG. 5 except that
a structure of an illumination device 40 partially varies. The
illumination device 40 shown in FIG. 6 has a feature that a light
mixing area 62 is provided between a diffusion sheet 60 and light
guide plates 51 and 52 of laminated light source units at a side of
a TFT-LCD 1.
[0217] The light mixing area 62 is formed of a transparent plate
made of acryl or polycarbonate, a diffused plate in which a minute
material having different refractivity, such as a fiber, is mixed
in the transparent plate or an air layer. When the air layer of a
space of 0.5 mm to 10 mm is used, as compared with a brightness
distribution .alpha. (identical to the brightness distribution
.alpha. of FIG. 5B) in the case where the air layer does not exist
and indicated by a broken line of FIG. 6B, a brightness
distribution .beta. indicated by a solid line is obtained in which
brightness irregularity at a boundary portion of the light-emitting
areas is relieved, and a brightness change is not visually
recognized.
[0218] According to this embodiment, minute brightness changes at
the boundary of the light-emitting areas are mutually mixed, and
transversal-shaped uneven brightness, which was visually recognized
at the boundary portion, can be relieved or eliminated.
[0219] Incidentally, in the illumination device 40 shown in FIGS.
5A and 6A, although all the light extraction structures 56 to 59 of
the light guide plates 50 to 53 are disposed at the lower side of
the light guide plates 50 to 53, when the light extraction
structures 56 and 59 of the first and the fourth light-emitting
areas 41 and 44 are disposed on the upper surfaces of the light
guide plates 50 and 53, the light extraction structures 56 to 59
are disposed on the one plane so that the brightness can be made
further uniform.
[0220] Next, a modified example of the illumination device of this
embodiment will be described with reference to FIGS. 7A to 7C. The
structure shown in FIG. 7A is the same as the structure shown in
FIG. 5A except that a structure of an illumination device 40
partially varies. The illumination device 40 shown in FIG. 7A has a
feature that a double-sided reflection member 64 to perform regular
reflection or diffuse reflection as shown in FIG. 7B or 7C is
disposed in a gap between light guide plates 51 and 52. At the
boundary portion of the second and the third light-emitting areas
42 and 43 of the illumination device 40 shown in FIGS. 5A and 6A,
part of the light is reflected toward the side of the light source
by surface reflection at the end face of the light guide plate, and
is again guided and the remainder is emitted from the end face and
is incident on the other illumination area. Thus, there is a
possibility that emitted lights are mixed and the motion picture
performance is degraded. Then, the double-sided reflection plate 64
is disposed in the gap between the light guide plates 51 and 52. By
this, the mixture of the emitted lights is prevented, and the
motion picture performance can be improved.
[0221] FIG. 7B shows such a structure that the opposite end faces
of the light guide plates 51 and 52 face with each other in
parallel and are substantially orthogonal to the light emission
surfaces of the light guide plates 51 and 52, and the double-sided
reflection member 64 made of a double-sided regular reflection
plate or a double-sided regular reflection sheet is disposed in the
gap.
[0222] FIG. 7C shows such a structure that a .LAMBDA.-shaped gap
opening to the rear surface side is provided at the opposite end
faces of the light guide plates 51 and 52, and the double-sided
reflection member 64 made of a double-sided regular reflection
plate or a double-sided regular reflection sheet is disposed in the
gap. Since the double-sided reflection member 64 shown in FIG. 7B
has a finite thickness, when viewed from the light emission side
(side of the TFT-LCD 1) of the light guide plates 51 and 52, the
gap is visually recognized as a shadow and the uneven brightness is
produced. On the other hand, when the structure as shown in FIG. 7C
is adopted, the double-sided reflection member 64 is not seen from
above, and the effect of improving the uneven brightness is
obtained. Incidentally, even when the structure is adopted such
that the light guide plates are in contact with each other in the
vicinity of the .LAMBDA.-shaped apex, a sufficiently superior
effect with respect to the motion picture performance can be
obtained.
[0223] When the refractivity of the light guiding material is n, it
is preferable that the apex angle .theta. of the .LAMBDA.-shaped
double-sided reflection member 64 satisfies
.theta..ltoreq.180.degree.-4.times.sin.sup.-1(1/n) . . .
(expression 1). In the case where the apex angle of the .LAMBDA.
shape is larger than .theta. of the above expression, part of the
light guided through the light guide plate and reflected at the end
face is emitted upward from the light guide plate. Thus, there is a
case where linear clear unevenness occurs on the liquid crystal
panel plane. Accordingly, when the apex angle .theta. satisfying
the above expression 1 is adopted, since the end face reflected
light is entirely guided, it becomes possible to prevent the uneven
brightness.
[0224] The expression 1 will be described with reference to FIGS.
8A and 8B. FIG. 8A is an enlarged view of FIG. 7C, and FIG. 8B
shows the course of light at the end face on the side of the light
guide plate 52. In FIG. 8B, the emission light of the light guide
plate 52 is composed of light beams scattered by the printed
scattering pattern of the light extraction structures 58 of the
lower surface of the light guide plate 52, and when the incident
light from the end face A is emitted to the light-emitting area
from the light guide plate 52, only a portion within the reach of
the light beam from the end face A comes to have high brightness,
and the uneven brightness occurs.
[0225] The apex angle .theta. is determined by the condition that
the incident light beam from the end face A is not emitted from the
emission surface of the light guide plate 52. Here, the incident
angle of the light beam incident on the end face A is made a, the
refraction angle of the light beam incident on the light guide
plate 52 from the end face A is made b, the incident angle of the
light beam incident from the end face A on the light-emitting area
opening surface of the light guide plate 52 is made c, and the
refractivity of the light guide plate 52 is made n. The incident
light from the .LAMBDA.-shaped end face A of the light guide plate
52 is refracted according to Snell's law.
sin(a)=n.times.sin(b) (1)
n.times.sin(c)=sin(d) (2)
[0226] Besides, the refraction angleeb and the incident angle c are
expressed by the following expression.
90.degree.=b+c+.theta./2 (3)
[0227] Here, ifed 90.degree., light incident on the light guide
plate 52 from the end face A is not emitted from the light guide
plate 52.
(4) Besides, since there is a possibility of incidence from any
direction, the incident angle a becomes .+-.90.degree..
[0228] The expression (1) can be modified to b=sin.sup.-1(1/n), and
the expression (2) can be modified to c=sin.sup.-1(1/n).
[0229] When these are substituted into the expression (3),
.theta.=180.degree.-4.times.sin.sup.-1(1/n)
[0230] From the condition of (4),
.theta.<180.degree.-4.times.sin.sup.-1(1/n).
[0231] For example, in the case of PMMA of a normal light guide
plate material, n=1.48, and accordingly, .theta.=9.97.degree..
[0232] Next, still another modified example of the illumination
device of this embodiment will be described with reference to FIGS.
9A to 9C. The structure shown in FIG. 9B is the same as the
structure shown in FIG. 5A except that a structure of an
illumination device 40 partially varies. FIG. 9A shows a rough
structure of the illumination device of this modified example and a
liquid crystal display device using the same. A TFT-LCD 1 shown in
FIG. 9A is the same as the TFT-LCD 1 of this embodiment explained
by use of FIG. 4, and structural elements having the same operation
and function are denoted by the same symbols and the description
will be omitted. FIG. 9B is a sectional view taken along line A-A
of FIG. 9A, and shows a section obtained by cutting the
illumination device (sidelight type backlight unit) 40, which is
used for the TFT-LCD 1 to support the motion picture display
according to this embodiment, along a plane orthogonal to a tube
axial direction of a cold cathode fluorescent lamp. FIG. 9C shows a
brightness distribution of illumination light from the illumination
device 40 at the rear surface side of a display area of the TFT-LCD
1.
[0233] The structure shown in FIG. 9A is the same as the structure
shown in FIG. 4 except that the structure of the illumination
device 40 partially varies. The illumination device 40 shown in
FIG. 9A has a feature that brightness adjusting volumes 70 to 73
are provided for light source power supply circuits 35 to 38,
respectively, and the quantities of emission lights from respective
light-emitting areas 41 to 44 can be finely adjusted and can be
made uniform.
[0234] Originally, the emission light quantities of the cold
cathode fluorescent lamps are different from each other. Thus,
there can arise a problem that the brightnesses of the first to the
fourth light-emitting areas 41 to 44 are different from each other.
As a countermeasure against this problem, it is conceivable that
the brightness of each of the cold cathode fluorescent lamps is
evaluated, and the cold cathode fluorescent lamps having the same
brightness are combined and used, however, there is a problem that
the manufacturing cost becomes high. On the other hand, according
to this structure, the uneven brightness is lowered at low cost,
and the display surface brightness can be made uniform.
[0235] As described above, according to this embodiment, the liquid
crystal display device which can obtain the uniform brightness
distribution and is suitable for the motion picture display can be
manufactured to be small and thin.
Third Embodiment
[0236] An illumination device according to a third embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 10A to 29 and FIG. 1
showing the first embodiment. This embodiment has been made to
solve the problem of the third related art, and realizes a display
device in which even if a lighting period of a cold cathode
fluorescent lamp of an illumination device is made short, light
emission brightness of the cold cathode fluorescent lamp is not
required to be raised, and a high quality motion picture image can
be obtained.
[0237] Subjective evaluation was performed as to whether or not a
difference in picture quality was felt in the case where a ratio
(duty rate) of a lighting time of a backlight unit in one frame
period was changed, and further, gradation data was processed and
transmissivity of liquid crystal was adjusted. It has been found
that even if the duty ratio is the same, according to image data, a
difference in picture quality from the original image is felt or is
not felt. Examples of the subjective evaluation result are shown in
FIGS. 10A and 10B. FIG. 10A shows the subjective evaluation result
at a duty ratio of 80%, and FIG. 10B shows the subjective
evaluation result at a duty ratio of 60%. The horizontal axis of
FIGS. 10A and 10B indicates an average value of all gradation data
of 64 gradations of 0 to 63 displayed on one frame. The vertical
axis indicates a ratio (%) of the number of pixels saturated in
brightness by processing of image data to the number of total
display pixels. When the number of high brightness pixels saturated
in brightness by adjustment of the transmissivity of the liquid
crystal is examined, it varies according to the content of the
image, and at both the duty ratio of 80% and the duty ratio of 60%,
when the ratio of the number of pixels saturated in brightness to
the number of all display pixels is 2% or less of the whole
display, the difference in picture quality from the original image
is not felt irrespective of the average value (average brightness
of the image) of all gradation data of the image. Although
individual illustration is omitted, it has been found that when the
ratio of the pixels saturated in brightness is 2% or less of the
whole, even if the duty ratio is lowered, the difference in picture
quality from the original image is not felt in any image.
[0238] From the above, pixels at a specified ratio and selected in
descending order of brightness in an image are made to have the
maximum display brightness, and the respective brightnesses of the
remaining pixels except for those are reproduced by lowering the
duty ratio of the light source of the backlight unit and raising
the transmissivity of the liquid crystal, so that it becomes
possible to make the quality of the motion picture display
equivalent to the original image even if the duty ratio is
lowered.
[0239] The liquid crystal display device according to this
embodiment has the same structure as the structure described in the
first and the second embodiments and shown in FIGS. 1 and 4. The
same structural elements as those of FIGS. 1 and 4 are denoted by
the same symbols and the detailed description will be omitted. A
TFT-LCD 1 includes an LCD panel 2 to modulate light transmissivity
of respective sub-pixels of red (R), green (G) and blue (B), which
are two-dimensionally arranged in a matrix form, on the basis of
gradation data. An illumination device 24 (or an illumination
device 40, hereinafter, the description will be given using the
illumination device 24) for irradiating light is provided at the
rear surface of a display area of the LCD panel 2. The illumination
device 24 includes light sources (cold cathode fluorescent lamps 30
to 33) and light source power supply circuits 35 to 38 for driving
them.
[0240] A control circuit 16 of this embodiment is provided with
various circuits for driving the TFT-LCD 1, and a display data
conversion circuit 20 for analyzing gradation data inputted from
the outside. FIG. 11 shows a rough operation procedure of the
display data conversion circuit 20. As shown in FIG. 11, the
display data conversion circuit 20 stores the gradation data of
pixels (combination of sub-pixels of R, G and B) of one frame
inputted to the control circuit 16 (step S1), obtains lightness
Y=r.times.R+g.times.G+b.times.B (r, g and b are real numbers
including a numerical value of 0) from the respective gradation
data (R, G, B) corresponding to the respective pixels (step S2),
and creates a histogram of the lightness Y of the image (step S3).
Next, the number M of pixels relating to an image display in one
frame is calculated (step S4), a specific number t=M.times.p of a
product of the number M of pixels and a specified brightness
saturation ratio p (step S5), and threshold lightness Y.alpha. is
determined from the histogram of the lightness Y of the image and
the specific number t (step S6). Next, the processed gradation data
is outputted to the plural data bus lines 8 on the basis of the
threshold lightness Y.alpha. (step S7), and specified duty ratio
data is outputted to the light source control part 22 for
controlling the light source power supply circuits 35 to 38 (step
S8). The light source control part 22 controls the light source
power supply circuits 35 to 38 on the basis of the duty ratio data,
and turns on the cold cathode fluorescent lamps 30 to 33 at the
specified duty ratio.
[0241] For example, the display data conversion circuit 20
determines the duty ratio so that the product of the maximum value
which the light transmissivity can take (maximum value which the
gradation data can take) and the illumination quantity (duty ratio)
of the illumination device 24 becomes equal to the threshold
lightness Y.alpha., the gradation data of the pixels of the
lightness Y higher than the threshold lightness Y.alpha. is
processed so that the light transmissivity comes to have the
maximum value, and in the other pixel, the gradation data is
processed so that the product of the processed gradation data and
the determined duty ratio becomes equal to the lightness Y of the
original gradation data of the pixel.
[0242] FIG. 12 is a flowchart showing a calculation of the
lightness Y in the display data conversion circuit 20 and a
procedure of histogram creation. The display data conversion
circuit 20 sequentially reads gradation data D (R, G, B) of one
frame stored in a not-shown storage device (memory) (steps S10 and
S11), sets a constant to be, for example, (r, g, b)=(0.2126,
0.7152, 0.0722), and calculates the lightness
Y=r.times.R+g.times.G+b.times.B for the read gradation data (R, G,
B) (step S12). Next, a variable s is set to 63 (step S13), and the
values of Y and s are compared with each other (step S14). If
Y.noteq.s, the procedure proceeds to step S15, 1 is subtracted from
the value of s, the comparison of the Y value and the value is
performed again at the step S14, and the steps S14 and S15 are
repeated until Y=s is established. If Y=s, the procedure proceeds
to step S16, 1 is added to a frequency L(s) indicating the number
of times of appearance of the lightness Y=s in one frame, and the
procedure returns to the step S10. For example, when the gradation
data (R, G, B)=(58, 30, 25) is read at the step S11, the lightness
Y=35 is calculated at the step S12, and 1 is added to the value of
the frequency L(35) indicating the number of times of appearance of
the lightness Y=35 in one frame (step S16). The procedure from the
step S10 to the step S16 is repeated by the number of gradation
data of one frame, so that the respective values of the frequencies
L(0) to L(63) of the lightness Y=0 to 63 in the one frame are
obtained, and the histogram L of the lightness Y is calculated.
[0243] FIG. 13 is a flowchart showing a procedure for calculating
the number M of pixels which an image occupies in the case where
the image exists only in a part of one frame (screen). Pixels of
two-dimensional arrangement are made to have m rows and n columns,
and it is assumed that when the lightness Y of gradation data (R,
G, B) at an i-th row and a j-th column is 0 (that is, black display
in a normally black mode), x(i)=y(j)=0 is made to be satisfied at a
pixel (x(i), y(i)), and in the other case, x(i)=y(j)=1 is made to
be satisfied. With respect to all pixels of the one frame, a
comparison between the lightness Y and the value 0 is made, and
x(i)=y(j)=0 or x(i)=y(j)=1 is substituted into a coordinate (x(i),
y(i)) of each pixel. Since the image is almost square, when all
pixels in a vertical or horizontal column or row become black (a
pixel which becomes black display has x(i)=y(j)=0), they are
regarded as a background, and the other pixels are selected as the
image and the number M is obtained. That is, the number of pixels
of x(i)=1 and the number of pixels of y(i)=1 are calculated, and
the product of both is obtained, so that the number M is obtained.
For example, in the case where pixels for display exist
substantially in the center of the frame, among pixels of xm rows
and yn columns in the whole frame, the number M of pixels is
obtained in a range except for x1 to xb rows, xc to xm rows, y1 to
yf columns and yg to yn columns in which all image signals are
0.
[0244] Specifically, in all i and j, from a state of x (i)=y(j)=0,
at step S20 of FIG. 13, variables are set to be i=1 and j=1, the
variable j=1 and a column value (n+1) are compared with each other
(step S21). If j=1<n+1, since reading of data is not performed
up to the final column n, the procedure proceeds to step S22, and
the lightness Y of a pixel (1, 1) of the first row and the first
column is read. Next, the read lightness Y and the value 0 (zero)
are compared with each other (step S23), and if Y>0, since
gradation data other than black exists in the pixel (1, 1), the
procedure proceeds to step S24, x(1) is set to the value 1, y(1) is
set to the value 1, and the procedure proceeds to step S25. In the
case of Y=0, the procedure proceeds to step S25 without executing
the step S24. In this case, the pixel remains x(1)=y(1)=0.
[0245] Next, at the step S25, the variable i=1 and the row value m
are compared with each other. If i=1<m, since data reading is
not performed up to the final row m, the value of i is increased by
one (step S26), the procedure again returns to the step S21, the
lightness Y of a next pixel (2, 1) is read, the lightness Y and the
value 0 are compared with each other (step S23), and if Y>0, the
setting of x(2)=1 and y(1)=1 is made at (x(2), y(1)) (step S24). By
repeating this operation up to i=m, the processing of the m pixels
at the column j=1 is ended.
[0246] Next, the procedure proceeds to step S27 from the step S25,
the value of i is set to the initial value 0, the value of the
variable j is increased by one, the procedure again returns to the
step S21, and the lightness Y of the pixel (1, 2) at the first row
and the second column is read. Next, the read lightness Y and the
value 0 (zero) are compared with each other (step S23), and if
Y>0, since gradation data other than black exists in the pixel
(1, 2), the procedure proceeds to the step S24, x(1) of (x(1),
y(2)) is set to the value 1, y(2) is set to the value 1, and the
procedure proceeds to step S25. In the case of Y=0, the procedure
proceeds to step S25 without performing the step S24. In this case,
the pixel remains x(1)=y(2)=0.
[0247] Next, at the step S25, the variable i=1 and the row value m
are compared with each other. If i=1<m, since data reading is
not performed up to the final row m, the value of i is increased by
one (step S26), the procedure again returns to the step S21, the
lightness Y of the next pixel (2, 2) is read, and the lightness Y
and the value 0 are compared with each other (step S23), and if
Y>0, the setting of x(2)=1 and y(2)=1 is made (step S24). By
repeating this operation up to i=m, the processing of the m pixels
at the column j=2 is ended. The above operation is repeated and
when the variable j becomes j=n+1 at the step S21, the procedure
proceeds to a "judgment" routine.
[0248] In the "judgment" routine, after i=0 and j=0 are set at step
S28, the value of i is increased by one at step S29, and the value
of x(i) is added to the variable x (step S30). This processing is
repeated up to i=m (row) (step S31), and when the value becomes
i=m, the procedure proceeds to step S32. By the processing up to
the step S31, the number x of pixels used for the image display in
the row direction is grasped.
[0249] Next, the value of j is increased by one at the step S32,
and the value of y(j) is added to the variable y (step S33). This
processing is repeated up to j=n (column) (step S34), and the
procedure proceeds to step S35 when j=n is obtained. By the
processing up to the step S34, the number y of pixels used for the
image display in the column direction is grasped.
[0250] Next, at the step S35, the product of the number x of image
display pixels in the row direction and the number y of image
display pixels in the column direction are obtained, and the number
M of image display pixels of the one frame is obtained.
[0251] FIG. 14 is a flowchart showing a procedure for calculating
the threshold lightness Y.alpha.. In this procedure, on the basis
of the number M of image display pixels and a specified number p,
the lightness Y lower than the highest lightness by t=Mp pixels in
sequence is made the threshold lightness Y.alpha.. The specified
number p indicates the ratio of pixels saturated in brightness by
image processing, and from the subjective evaluation result shown
in FIG. 10, it is preferable that the number p is p=0.02 (=2%) or
less. When the specified number p is 2%, and the number M of image
display pixels is 80000, the specified number t=Mp=80000.times.2
(%)=1600. In order to select 1600 lightnesses Y in descending order
of lightness, i=63 is set at step S1, and the initial value of the
frequency L is set to L=L(63) (step S41).
[0252] At step S42, t=1600 and L=L(63) are compared with each
other, and if the frequency L(63) is larger, the procedure proceeds
to step S45, and the threshold lightness is made Y.alpha.=63. If
t=1600.gtoreq.L=L(63), 1 is subtracted from i=63 at step S43 to
make i=62, and L=L(63)+L(62) is calculated at step S44. The
procedure again returns to the step S42, t=1600 and the calculated
L are compared with each other, and if the frequency L is larger
than t, the procedure proceeds to the step S45, and the threshold
lightness is made Y.alpha.=62. If t=1600.gtoreq.L,
L=L(63)+L(62)+L(61) . . . is repeated to obtain Y.alpha.. In this
routine, although the lightness L is sequentially added like
L(63)+L(62)+L(61), it is needless to say that a judgment may be
sequentially made as to, for example, whether 1600-L(63) is 0 or
higher, and whether 1600-L (63)-L (62) is 0 or higher.
[0253] When the threshold lightness Y.alpha. is obtained by the
procedure shown in FIG. 14, next, a control value of illumination
is determined. For example, it is assumed that the display is a
64-gradation display, .gamma. (gamma) correction or the like is
carried out, and the characteristics of gradation and brightness
are determined. FIG. 15 shows a duty ratio selection lookup table
used for selection of a duty ratio of a light source. In the table
shown in FIG. 15, the duty ratio (%) is determined to correspond to
the value of the threshold lightness Y.alpha. obtained by the
procedure shown in FIG. 14.
[0254] Although the duty ratio may be obtained by calculation, in
the case where a calculation expression is complicated, it is
simpler to prepare the table as shown in FIG. 15. The duty ratio
selection lookup table is stored in a not-shown memory in the
display data conversion circuit 20. The display data conversion
circuit 20 selects the specified duty ratio data from the table on
the basis of the threshold lightness Y.alpha., and outputs it to
the light source control part 22. The light source control part 22
controls the light source power supply circuits 35 to 38 on the
basis of the inputted duty ratio data, and drives the cold cathode
fluorescent lamps 30 to 33 at the specified duty ratio.
[0255] FIG. 16 shows a signal control value selection lookup table
to determine control values when the processed gradation data are
outputted to the plural data bus lines 8, which are made to
correspond to the threshold lightness Y.alpha.. In the table, the
uppermost row indicates the threshold lightness Y.alpha. in
descending order from the left to the right, and the leftmost
column indicates the original gradation in descending order. For
example, in the case where the display brightness is 360 cd at the
threshold lightness Y.alpha.=60 and 400 cd at the maximum threshold
lightness Y.alpha.=63, the original gradation data is processed so
that at the lightness Y=63 to 60, the light transmissivity in the
liquid crystal layer becomes 100%. Besides, the original gradation
data is processed so that at the lightness Y.ltoreq.59, the light
transmissivity of the liquid crystal layer becomes 400/360=10/9
times as high as the original light transmissivity. That is, the
light transmissivity is converted to such light transmissivity that
the display output brightness Ii of the lightness Yi not higher
than the lightness Y.alpha. becomes (I/I.alpha.) times as high.
When the control values are made the table as shown in FIG. 16 and
are stored in a memory, an arithmetic processing performed at all
times can be omitted.
[0256] Besides, the duty ratio is determined by the lighting of a
light-emitting part in accordance with the ratio of the output
display brightness I.alpha. of the threshold lightness Y.alpha.
with respect to the maximum display output brightness I (=maximum
light transmissivity.times.maximum illumination quantity).
[0257] By combining the structure and the procedure shown in FIGS.
11 to 16, the calculation of the lightness Y and the creation of
the histogram L are performed while the gradation data (image data)
of the one frame is read into a memory, and after all gradation
data is read, the number M of image display pixels is calculated,
the specific value t=Mp is calculated while the number p is made
p=2%, and the threshold lightness Y.alpha. can be obtained. The
duty ratio is selected by use of the table shown in FIG. 15 and is
outputted to the light source control part 22, and in
synchronization with this, gradation data processed in accordance
with the table shown in FIG. 16 are outputted to the respective
data bus lines 8.
[0258] FIG. 17 shows an example of duty driving. The horizontal
direction indicates time, and the vertical direction indicates
lighting (On) and non-lighting (Off) of the light sources 30 to 33.
From the left to the right, the drawing shows a duty ratio of 100%
(lighting in the whole frame), a duty ratio of 50% (lighting in the
latter 50% of the frame), and a duty ratio of 20% (lighting in 20%
before the last of the frame).
[0259] As a specific example, a display device was fabricated in
which a circuit as described above was constructed into an FPGA, a
display area was 17 inch wide, a sidelight type backlight
(fluorescent lamp was disposed above and below a display) or a
direct type 8-lamp backlight was used, and display brightness was a
brightness of 200 to 800 nit. A motion picture was reproduced using
a commercially available DVD, the display device of this embodiment
and a conventional normal display device were disposed side by
side, and a comparison between motion picture images was made. As a
result, it was confirmed that an image comparable to a conventional
display could be obtained also in the display device of this
embodiment. Besides, when the duty ratio of the backlighting of the
conventional illumination device was made 100%, it was found that
the average of the duty ratio of the display device of this
embodiment was 50%, and an effect of power saving in the backlight
could be obtained.
[0260] Besides, when the value of p (>2%) is made further large,
if the pixels of the lightness Y exceeding the threshold lightness
Y.alpha. are discrete, the influence on the picture quality is
small, however, when the pixels are concentrated, there is a case
where it is judged that the picture quality is degraded. Besides,
especially in the case where the pixels are concentrated at the
center of the screen, even if p is the same, there is a case where
it is judged that the picture quality is degraded, and accordingly,
it is needless to say that the collective/discrete state of pixels
is extracted as data and may be used for preventing the picture
quality degradation. In this case, the M pixels are divided into
several partitions, and the numbers of elements in the respective
partitions are made M1 to Ms, and the above procedure is used in
each the elements of M1 to Ms.
[0261] Incidentally, a frame memory or the like did not exist in
the control circuit 16, and even if the operation of this
embodiment was applied with a delay of one frame ( 1/60 sec) while
the image data was directly sent as the display data, in the motion
picture by the commercially available DVD or the like, there did
not occur a trouble that the image was seen to be odd or dark.
[0262] Besides, when the lightness Y was 0 to 255 (256 gradations),
although the illumination control values and the signal control
values should have been made the lookup table with respect to the
threshold lightness Y.alpha.=0 to 255, the control values were
simplified to 0 to 64, and the respective control values were
converted into 0 when the threshold lightness Y.alpha.=0; 1 when
the threshold lightness Y.alpha.=1 to 4; 2 when the threshold
lightness Y.alpha.=5 to 8; . . . ; 64 when the threshold lightness
Y.alpha.=253 to 255, and a display was carried out and the motion
picture was observed, and as a result, an excellent result was
obtained on the whole.
[0263] FIGS. 18 to 27 show specific examples. FIG. 18 shows an
example in which a sidelight type backlight unit is disposed in an
LCD panel. Cold cathode fluorescent lamps A and B are disposed at
an upper part and a lower part of a display area P. FIG. 19 shows
an example in which the cold cathode fluorescent lamps A and B
shown in FIG. 18 are duty driven. The horizontal direction
indicates time, and the vertical direction indicates lighting (On)
and non-lighting (Off) of the cold cathode fluorescent lamps A and
B. From the left to the right in the drawing, although the duty
ratio is 80% in both the cold cathode fluorescent lamps A and B in
the first frame, the cold cathode fluorescent lamp A is turned on
in 80% of the latter half of the frame, and the cold cathode
fluorescent lamp B is turned on in 80% of the former half of the
frame. In a next frame, although the duty ratio is 40% in both the
cold cathode fluorescent lamps A and B, the cold cathode
fluorescent lamp A is turned on in 40% of the latter half of the
frame, and the cold cathode fluorescent lamp B is turned on in 40%
of the former half of the frame.
[0264] FIG. 20 shows a scan type backlight unit in which cold
cathode fluorescent lamps A to F are disposed at the rear surface
of a panel display surface. FIG. 21 shows an example in which the
cold cathode fluorescent lamps A to F are duty driven. The
horizontal direction indicates time, and the vertical direction
indicates lighting (On) and non-lighting (Off) of the cold cathode
fluorescent lamps A to F. From the left to the right in the
drawing, the duty ratio becomes 40% from 80% in all of the cold
cathode fluorescent lamps A to F. At this time, the lighting start
points (or non-lighting points) of the cold cathode fluorescent
lamps A to F are sequentially shifted by a specified time, and a
scan state is formed.
[0265] FIG. 22 shows an example in which a sidelight type backlight
unit is disposed in an LCD panel. Cold cathode fluorescent lamps A
and B are disposed on the right and the left with respect to the
upper center of a display area P, and cold cathode fluorescent
lamps C and D are disposed on the right and the left with respect
to the lower center of the display area P. An image P1 is displayed
on the left with respect to the center of the display area P, and
an image P2 is displayed on the right. FIG. 23 shows an example in
which the cold cathode fluorescent lamps A to D shown in FIG. 22
are duty driven.
[0266] FIG. 24 shows an example in which a direct type backlight
unit is disposed in an LCD panel. Cold cathode fluorescent lamps A,
C, E and G are disposed on the left with respect to the center of a
display area P, and cold cathode fluorescent lamps B, D, F and H
are disposed on the right with respect to the center of the display
area P. An image P1 is displayed on the left with respect to the
center of the display area P, and an image P2 is displayed on the
right. FIG. 25 shows an example in which the cold cathode
fluorescent lamps A to H shown in FIG. 24 are duty driven.
[0267] FIG. 26 shows an example in which a direct type backlight
unit is disposed in an LCD panel. LEDs A to C, H to J, K to M and P
to R are disposed in a matrix form on the 2/3 portion of the
display area P at the left with respect to the center thereof, and
LEDs D, E, I, J, N, O, S and T are disposed in a matrix form on the
1/3 portion of the display area P at the right with respect to the
center thereof. An image P1 is displayed on the 2/3 portion of the
display area P at the left with respect to the center thereof, and
an image P2 is displayed on the 1/3 portion at the right. FIG. 27
shows an example in which the LEDs A to T shown in FIG. 26 are duty
driven.
[0268] In an arbitrary display area of the display device shown in
the above specific examples, as the emission time of the backlight
becomes short, a blur of a motion picture image intrinsic to the
liquid crystal display device can be improved.
[0269] In the above examples, although the average of the duty
ratio of the backlight is 50%, when an image becomes clear in
total, the duty ratio approaches 100%. When the duty ratio
approaches 100%, the effect of improving the blur of the motion
picture image becomes low. Then, as described in the first and the
second embodiments, two kinds of lighting states, that is, the
whole lighting state and the intermediate lighting state are
provided in one frame, and the intermediate brightness as the
display brightness at the time of the intermediate lighting is set
to 50% of the whole lighting brightness as the display brightness
at the time of the whole lighting.
[0270] For example, in the display device including the scan type
backlight shown in FIG. 1 in which one frame is divided into four
areas in sequence from the above, and duty driving is performed in
the respective areas, it is assumed that as shown in FIG. 28, the
duty ratio is 80%, the first 20% of the one frame period is put in
the non-lighting state, and the remaining 80% of the period is put
in the whole lighting state. In this case, in a period between a
point T2 of the first 20% (first area) of the one frame period and
a point T3 of 25%, in spite of the fact that the gradation data is
in the middle (indicated by V in the drawing) of a writing period
T1 to a pixel, the backlight is changed at the point T2 from the
non-lighting state S1 to the maximum lighting state S2. Besides,
the backlight is turned off at the time of high transmissivity
before next gradation data is written. In the one frame period,
since the area of 20%, in total, of the four areas is in the
lighting state when the gradation data is written, and are in the
non-lighting state immediately before the next gradation data is
written, the light quantity is felt to be lower than that in the
remaining area of 80%, and the display quality is degraded.
[0271] FIG. 29 shows a duty driving method for solving the above
conventional problem. As shown in FIG. 29, in the first 40% of one
frame period, the backlight is put in the intermediate lighting
state S3 (gradation data is written into a pixel in the time T1 of
the first 25% of the one frame period). Next, the backlight is put
in the maximum lighting state in the remaining 60%. By doing so,
the display brightness visually sensed does not change, and
illumination is performed by the whole lighting at the point when
the liquid crystal almost completes the response, and therefore, a
desired image is branded on the eye. Accordingly, the motion
picture blur of the image does not occur all over the display area
and the excellent display quality is obtained.
[0272] As described above, according to this embodiment, pixels
having a specified ratio and selected in descending order of
brightness in a motion image are made to have the maximum display
brightness, and the respective brightnesses of the remaining pixels
except for those are reproduced by lowering the duty ratio of the
backlight and raising the transmissivity of the liquid crystal. By
this, even if the duty ratio of the backlight is lowered, it is
possible to make the motion picture display quality equivalent to
the original image, and power saving of the backlight becomes
possible. Besides, by the combination with a scan type backlight or
a blinking type backlight, it is possible to realize a higher
quality liquid crystal display device in which the image blur is
improved while the display quality of the motion picture image is
kept. Incidentally, although this embodiment is applied to the
liquid crystal display device, it can also be used for emission
control of an EL (Electro Luminescence) element.
Fourth Embodiment
[0273] An illumination device according to a fourth embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 30 to 51. According to
duty driving, in synchronization with a writing timing of gradation
data, the brightness of a light source of an illumination device
which performs plane emission is directly modulated, however, the
degree of modulation is conventionally very high, and it has been
considered that the degree is required to make, for example, a
brightness ratio of 20 or higher. However, as described in the
first embodiment, even if the duty driving in which the light
source is completely turned on or off is not used, the display
quality of the motion picture is not degraded. The present inventor
et al. have found that when the brightness ratio is 2 or higher, a
sufficient display can be obtained. By performing new duty driving
described below in accordance with this finding, the display can be
made to have high brightness without damaging the display quality
of the motion picture, luminescence efficiency (electric power
ratio) of the cold cathode fluorescent lamp can be made high, and
the electric power can be reduced. Further, the lifetime of the
light source can be prolonged, and the power source can be made
small, light and thin.
Example 4-1
[0274] FIG. 30 shows a backlight structure of example 1 of this
embodiment. In this example, a TFT-LCD 1 of the first embodiment
shown in FIG. 1 is used, and FIG. 30 shows a state in which an
illumination device 24 is seen from the side of light emission
openings of a first to a fourth light-emitting areas. At the side
of the light emission openings, a diffusion sheet 60 or the like
described in the second embodiment is also disposed. The backlight
is of the direct type. Other than that, this illumination device is
the similar as the illumination device 24 shown in FIG. 1. FIG. 31
shows driving waveforms of the backlight of the example 1. FIG. 31
is substantially the same as FIG. 2, and is identical in that it
shows output timings of gate pulses GP outputted to gate bus lines
6 from a gate driver 12, however, there is a difference in that
FIG. 2 shows the light emission brightnesses B(25) to B(28), while
FIG. 31 shows currents C(30) to C(33) fed to cold cathode
fluorescent lamps 30 to 33 of the respective light-emitting areas
25 to 28.
[0275] As shown in FIG. 31, the currents to be fed to the
respective cold cathode fluorescent lamps 30 to 33 are duty driven
so that gradation data is written into a specified pixel, the
liquid crystal sufficiently responds and the transmissivity becomes
high, and then, illumination is performed in the maximum lighting
state S2. Although the current states (or electric power states) of
the respective cold cathode fluorescent lamps 30 to 33 have the
maximum current (or maximum electric power) when illumination is
performed at the maximum light quantity, a current is fed (or
electric power is supplied) at the other time as well, and the
intermediate lighting state S3 is kept. In this duty driving, the
above current state (or electric power state) is repeated at the
same cycle as the writing cycle of display data. As stated above,
this example has a feature that even when the maximum current (or
maximum electric power) is not fed, a current is fed (or electric
power is supplied).
[0276] In the duty driving, whether a human being senses a motion
picture blur of a motion picture display or a tailing phenomenon
greatly depends on a maximum value of illumination light quantity
in the maximum irradiation state S2 and a time length. Even if the
intermediate lighting state S3 of about one half of the maximum
value is made to occur between the maximum lighting states S2
repeated at a specified frequency, the quality of the motion
picture display is not changed.
[0277] Thus, according to this embodiment, since the brightness can
be made high while an increase in electric power is suppressed, it
is not necessary to enlarge a stabilizer of the cold cathode
fluorescent lamp, and the stabilizer is made light and thin, and
can be manufactured at low cost. Further, since a rise in drive
voltage due to an increase in current in the related art can also
be suppressed, a drop in current-to-light conversion efficiency of
the cold cathode fluorescent lamp is suppressed, and the tube
lifetime can be made long. As stated above, as compared with the
conventional system in which illumination is performed in the
maximum lighting state S2 only for a specified time, and
illumination is not performed for a time other than that, according
to this embodiment, the quality of the motion picture display is
equivalent, and it is possible to raise the brightness, to reduce
the electric power, to reduce the weight, thickness and size of the
device, and to prolong the lifetime.
Example 4-2
[0278] FIG. 32 shows a backlight structure of example 2 of this
embodiment. In this example, a TFT-LCD 1 similar to the example 1
is used, and FIG. 32 shows a state viewed in the same direction as
FIG. 30 of the example 1. The backlight is of the direct type. Two
cold cathode fluorescent lamps (30a, 30b), (31a, 31b), (32a, 32b)
and (33a, 33b) are disposed in the respective light-emitting areas
25 to 28.
[0279] FIG. 33 shows drive waveforms of the backlight of the
example 2. Although the respective waveforms of FIG. 33 are
substantially the same as those of FIG. 31 of the example 1, in
this example, since each of the light-emitting areas 25 to 28 is
illuminated by the pair of cold cathode fluorescent lamps, there is
a merit that the respective current waveforms shown in FIG. 33 can
be realized by the combination of the two cold cathode fluorescent
lamps.
[0280] A description will be given more specifically with reference
to FIGS. 34 to 36. FIGS. 34 to 36 show timing charts similar to
FIG. 33. In a case shown in FIG. 34, illumination driving is
performed by supplying such current to the cold cathode fluorescent
lamps 30a, 31a, 32a and 33a of the respective light-emitting areas
that the maximum lighting state S2 occurs at a specified cycle, and
the non-lighting state S1 occurs at the other time. Besides,
illumination driving is performed by supplying such current to the
cold cathode fluorescent lamps 30b, 31b, 32b and 33b of the
light-emitting areas that the non-lighting state S1 occurs in the
maximum lighting state S2 of the paired cold cathode fluorescent
lamps 30a, 31a, 32a and 33a, and the intermediate lighting state S2
occurs at the other time. By this, it is possible to perform
illumination with the brightness equal to the brightness obtained
by the illumination driving current waveforms shown in FIG. 33.
[0281] In a case of FIG. 35, the cold cathode fluorescent lamps
30a, 31a, 32a and 33a of the light-emitting areas are respectively
driven by such low current that an intermediate lighting state S2'
lower than the maximum lighting state S2 occurs at a specified
cycle, and at the other time, the lamps are driven by such low
current that an intermediate lighting state S3-1 lower than the
intermediate lighting state S3 shown in FIG. 33 occurs. The
respective cold cathode fluorescent lamps 30b, 31b, 32b and 33b of
the light-emitting areas are driven by such low current that a
differential intermediate lighting state S3-3 occurs at the
intermediate lighting state S2' of the respective paired cold
cathode fluorescent lamps 30a, 31a, 32a and 33a so that the total
becomes the maximum lighting state S2, and are driven by such low
current that a differential intermediate lighting state S3-2 occurs
at the intermediate lighting state S3-1 of the respective cold
cathode fluorescent lamps 30a, 31a, 32a and 33a so that the total
becomes the intermediate lighting state S3. By this, it is possible
to perform illumination with the brightness equal to the brightness
obtained by the illumination driving current waveforms shown in
FIG. 33.
[0282] In a case shown in FIG. 36, the cold cathode fluorescent
lamps 30a, 31a, 32a and 33a of the respective light-emitting areas
are driven by such low current that an intermediate lighting state
S2'' lower than the maximum lighting state S2 occurs at a specified
cycle, and the current supply is interrupted at the other time so
that the non-lighting state S1 occurs. The cold cathode fluorescent
lamps 30b, 31b, 32b and 33b of the respective light-emitting areas
are continuously driven by such low current that a differential
intermediate lighting state S3 occurs at the intermediate lighting
state S2'' of the respective paired cold cathode fluorescent lamps
30a, 31a, 32a and 33a so that the total becomes the maximum
lighting state S2. By this, it is possible to perform illumination
with the brightness equal to the brightness obtained by the
illumination driving current waveforms shown in FIG. 33.
[0283] As stated above, by controlling the current fed to the pair
of the cold cathode fluorescent lamps of the respective
light-emitting areas 25 to 28, the illumination state shown in FIG.
33 can be obtained. By performing the duty driving shown in this
example, the brightness can be raised while the increase in
electric power is suppressed, and accordingly, it is not necessary
to enlarge the stabilizer of the cold cathode fluorescent lamp, and
the stabilizer can be made light and thin, and can be manufactured
at low cost. Further, since the rise in drive voltage due to the
increase in current as in the related art can also be suppressed,
the drop in the current-to-light conversion efficiency of the cold
cathode fluorescent lamp is suppressed and the tube lifetime can be
made long. As stated above, according to this embodiment, the
quality of the motion picture display is the same, and it is
possible to raise the brightness, to reduce the electric power, to
reduce the weight, thickness and size of the device, and to prolong
the lifetime.
Example 4-3
[0284] An example 3 will be described with reference to FIGS. 37
and 38. FIG. 37 shows drive waveforms of backlights similarly to
FIG. 31 of the example 1. The backlight structure of this example
is the same as that of the example 1 shown in FIG. 30. In a case
shown in FIG. 37, the cold cathode fluorescent lamps 30, 31, 32 and
33 of the respective light-emitting areas are driven by such
current that the maximum lighting state S2 occurs at a specified
cycle, and at the other time, they are driven by such low current
(50% of the current value of the maximum lighting state S2) that
the intermediate lighting state S3 occurs, and further, a period in
which the current supply is stopped is provided so that when the
maximum lighting state S2 is changed to the intermediate lighting
state S3, the non-lighting state S1 occurs only for a specified
time.
[0285] In the case shown in FIG. 38, the cold cathode fluorescent
lamps 30, 31, 32 and 33 of the respective light-emitting areas are
driven by such current that the maximum lighting state S2 occurs at
a specified cycle, and at the other time, they are driven by such
low current (50% of the current value of the maximum lighting state
S2) that the intermediate lighting state S3 occurs, and when the
maximum lighting state S2 is changed to the intermediate lighting
state S3, there is provided a period in which low current (20% of
the current value of the maximum lighting state S2) is supplied
such that an intermediate lighting state S4 clearer than the
non-lighting state S1 and darker than the intermediate lighting
state S3 occurs only for a specified time.
[0286] As shown in FIGS. 37 and 38, the current value (or electric
power or light quantity value) is instantaneously and largely
reduced immediately after the state of the maximum current value
(or maximum electric power or maximum light quantity value), so
that the image is instantaneously visually recognized and
disappears immediately thereafter, and an impulse effect felt by a
human being can be made great.
[0287] FIG. 39 shows a graph in which the current value (relative
value) at the maximum lighting state S2 is made 10, the
intermediate lighting states S3 and S4 in FIG. 38 are changed, and
the display quality obtained at the time when a motion picture
display is carried out on the display area of the TFT-LCD 1 is
graphed as subjective evaluations by plural observers.
[0288] In FIG. 39, the horizontal axis indicates the ratio (%) of
the maximum lighting state S2 to one frame period f, and the
vertical axis indicates the evaluation according to evaluation
points of from first to fifth stages. The evaluation point 1
indicates a case where a motion picture blur, a tailing phenomenon
and the like on the motion picture display are "very obstructive",
and the evaluation point 2 indicates a case where those becomes
"obstructive". The evaluation point 3 indicates a case where the
motion picture blur is "annoying but tolerable", the evaluation 4
indicates a case where "a difference is seen but is tolerable", and
the evaluation point 5 indicates a case where "picture quality is
equivalent to a still picture and is excellent".
[0289] In the drawing, a straight line (A) connecting circular
marks indicates a case of (current value of the maximum lighting
state S2, current value of the intermediate lighting state S4,
current value of the intermediate lighting state S3)=(10, 10, 10).
In this case, irrespective of the ratio of the maximum lighting
state S2 to the one frame period f (hereinafter abbreviated to
"ratio of the maximum lighting state S2"), illumination is
performed with the maximum brightness level in the whole area of
the one frame period f. That is, the display is equivalent to the
hold type driving, and accordingly, the image quality is such that
the motion picture blur and the tailing phenomenon becomes very
obstructive, and the evaluation point becomes 1.
[0290] In the drawing, a polygonal line (B) connecting x marks
indicates a case of (current value of the maximum lighting state
S2, current value of the intermediate lighting state S4, current
value of the intermediate lighting state S3)=(10, 5, 5). In this
case, when the ratio of the maximum lighting state S2 is in the
range of from about 10% to 30%, the motion picture blur and the
tailing phenomenon are hardly visually recognized, and the
excellent image quality is obtained, so that the evaluation point
is 4. Besides, when the ratio of the maximum lighting state S2
exceeds 30%, the evaluation is gradually lowered, however, the
evaluation point 3 is obtained up to about 50%.
[0291] A polygonal line (C) indicates a case of (current value of
the maximum lighting state S2, current value of the intermediate
lighting state S4, current value of the intermediate lighting state
S3)=(10, 2, 5). In this case, when the ratio of the maximum
lighting state S2 is within the range of from about 10% to 30%, the
motion picture blur and the tailing phenomenon are hardly visually
recognized, and the excellent image quality is obtained, so that
the evaluation point is close to 5. Besides, when the ratio of the
maximum lighting state S2 exceeds 30%, the evaluation is gradually
lowered, however, the evaluation point 3 is obtained up to about
50%.
[0292] In the drawing, a polygonal line (D) connecting black
circular marks indicates a case of (current value of the maximum
lighting state S2, current value of the intermediate lighting state
S4, current value of the intermediate lighting state S3)=(10, 0,
5). In this case, when the ratio of the maximum lighting state S2
is within the range of from about 10% to 30%, the motion picture
blur and the tailing phenomenon are hardly visually recognized, and
the excellent image quality is obtained, so that the evaluation
point is close to 5. Besides, when the ratio of the maximum
lighting state S2 exceeds 30%, the evaluation is gradually lowered,
however, the evaluation point 3 or higher is obtained up to about
50%.
[0293] In the drawing, a polygonal line (E) connecting square marks
indicates a case of (current value of the maximum lighting state
S2, current value of the intermediate lighting state S4, current
value of the intermediate lighting state S3)=(10, 0, 0). This is
the same as the illumination method of the conventional scan type
LCD. In this case, when the ratio of the maximum lighting state S2
is within the range of from about 10% to 30%, the motion picture
blur and the tailing phenomenon are hardly visually recognized, and
the excellent image quality is obtained, so that the evaluation
point becomes further close to 5. Besides, when the ratio of the
maximum lighting state S2 exceeds 30%, the evaluation is gradually
lowered, however, the evaluation point 3 or higher is obtained up
to about 50%.
[0294] From FIG. 39, it is understood that even if the intermediate
lighting state S3 is made the brightness level of about 30% of the
brightness level of the maximum lighting state S2, it is possible
to obtain the display quality comparable to the conventional scan
type LCD indicated by the polygonal line (E). Further, the
brightness level of the intermediate lighting state S3 up to about
50% of the brightness level of the maximum lighting state S2 can be
regarded as being in the allowable range.
[0295] Besides, when the illumination time of the maximum lighting
state S2 is 30% or less of the one frame time f, the motion picture
blur and the tailing phenomenon hardly occur, and the time up to
50% can be regarded as being in the allowable range.
[0296] FIG. 40 shows characteristics of a cold cathode fluorescent
lamp, the horizontal axis indicates current fed to the cold cathode
fluorescent lamp, and the vertical axis indicates a duty ratio. In
the drawing, two thick solid lines indicate contour lines of
supplied electric power, one of them indicates a case of an
electric power of 1.0, and the other indicate a case of an electric
power of 0.6. The other nine thin solid lines indicate contour
lines of brightness when the brightness from a brightness of 20 to
a brightness of 100 is divided at intervals of ten. From FIG. 40,
it is understood that as the value of the current fed to the cold
cathode fluorescent lamp becomes large, the current-to-light
conversion efficiency of the cold cathode fluorescent lamp is
lowered, and there is a remarkable tendency that the lifetime
becomes short. Besides, with respect to a stabilizer for driving
the cold cathode fluorescent lamp, when the value of the current to
be fed becomes large, it becomes necessary to enlarge a transformer
and the like, so that the stabilizer becomes heavy, thick and
expensive.
[0297] According to this embodiment, it is possible to solve the
problem of the current-to-light conversion efficiency of the cold
cathode fluorescent lamp and the tube lifetime as shown in FIG. 40.
FIGS. 41A and 41B and FIGS. 42A and 42B show effects in the case
where the illumination device of this embodiment and the duty
driving method thereof are used. The horizontal axis shown in FIGS.
41A and 41B and FIGS. 42A and 42B indicates time, and the vertical
axis indicate light quantity.
[0298] FIG. 41A shows conventional duty driving, and shows light
quantity when the electric power is 1.0 (arbitrary unit:
hereinafter abbreviated to a.u.) and a current of 32 mA is fed to
the cold cathode fluorescent lamp at a duty ratio of 33%, and shows
a state in which a (time average) brightness of 1.0 (a.u.) is
obtained by this. On the other hand, FIG. 41B shows duty driving
according to this embodiment, and shows the light quantity when the
electric power is 1.0 (a.u.), a current of 13 mA is fed in the
maximum lighting state S2 to the cold cathode fluorescent lamp at a
duty ratio of 33%, and a current of 5.2 mA is supplied to the cold
cathode fluorescent lamp in the remainder of 67% to produce the
intermediate lighting state S3. By this, a brightness of 1.4 (a.u.)
is obtained.
[0299] As stated above, according to this embodiment, when the
electric power is constant, as compared with the related art, the
brightness becomes 1.4 times as high, and the current-to-light
conversion efficiency also becomes 1.4 times as high. According to
this embodiment, a large current value may be 13 mA which is of a
conventional value. By this, for example, when the electric power
is the same, a conventional display device having a display
brightness of 300 candela can be made to have a brightness of 420
candela without damaging the motion picture quality. Further, the
stabilizer is light, thin, short and small, and can be produced at
low cost.
[0300] FIG. 42A is the same as FIG. 41A. On the other hand, FIG.
42B indicates duty driving according to this embodiment, and shows
light quantity when the electric power is 1.0 (a.u.), a current of
32 mA similar to the conventional case is fed to the cold cathode
fluorescent lamp in the maximum lighting state S2 at a duty ratio
of 33%, and a current of 7 mA is supplied to the cold cathode
fluorescent lamp in the remainder of 67% to produce the
intermediate lighting state S3. According to this, the electric
power 1.5 times as large as that of the conventional system can be
supplied, and the display brightness can be doubled. That is,
according to this embodiment, while the same stabilizer is used, a
display device having a display brightness of 300 candela in the
conventional system can be made to have a brightness of 600 candela
without damaging the motion picture quality. Further, the
current-to-light conversion efficiency can also be improved by a
factor of 1.33.
Example 4-4
[0301] An example 4 will be described with reference to FIGS. 43A
and 43B. FIG. 43A shows a simple section of a backlight unit 75 of
this example. The left side of the drawing corresponds to the upper
side of the display area of the LCD panel 2 shown in FIG. 1, and
the right side of the drawing corresponds to the lower side of the
display area. For example, 12 cold cathode fluorescent lamps 76a to
761 are divided into groups each including four lamps, and are
provided in such a way that their tube axes are substantially in
parallel to the gate bus lines 6. The cold cathode fluorescent
lamps 76a to 761 are contained in thin dish-like housings, and
diffuse reflection plates 77 are disposed on the inner walls of the
housings. The lights from the cold cathode fluorescent lamps 76a to
761 are emitted to a not-shown LCD panel 2 in FIG. 43A through a
diffused plate 78 provided at light emission openings. When this
structure is seen as a hold type LCD backlight unit, it is a normal
structure. Since scan driving is not performed, partitions do not
exist between the respective illumination areas.
[0302] In the backlight unit 75 of the structure as stated above,
when the light source is duty driven, light overflows into the
surrounding area as well, and the effect of suppressing the motion
picture blur is sufficiently obtained even if the partition is not
provided, and further, when the duty driving of this embodiment is
performed, the effect of high brightness, power saving, long
lifetime and the like can be further obtained. FIG. 43B shows a
relation between a frame position and brightness at an instant in a
period in which the cold cathode fluorescent lamps 76a to 761 are
scan driven at a duty ratio of 33% in the backlight unit 75 of the
structure shown in FIG. 43A so that any four adjacent lamps are
always turned on. The left side of the drawing corresponds to the
upper side of the display area of the LCD panel 2 shown in FIG. 1,
and the right side of the drawing corresponds to the lower side of
the display area. Although a curved line at an X position becomes
smooth by a persistence time (8 ms) of a G (green) fluorescent
substance in the cold cathode fluorescent lamp and the tailing
phenomenon occurs, the picture quality capable of sufficiently
supporting a motion picture is obtained.
[0303] FIG. 44 shows a result obtained when the duty driving shown
in FIG. 37 or 38 is performed to the backlight unit 75. The
horizontal axis and the vertical axis of FIG. 44 are the same as
FIG. 43B. An X position of a curved line shown in FIG. 44 is
steeper than that shown in FIG. 43B, and it is understood that the
tailing phenomenon is more effectively suppressed.
[0304] More specifically, in the normal direct type backlight shown
in FIGS. 43A, 43B and 44, the duty driving of this embodiment is
used, and a current supply state is not simply made to have two
values (on/off) as in the related art, but is made to have the
flatness in a state of a small light quantity. Besides, the
brightness distributions (illumination light quantity
distributions) of FIGS. 43B and 44 are realized by experimentally
making an adjustment, as current modulation performing smooth
temporal change, in view of illumination light quantity from the
other cold cathode fluorescent lamps, and the persistence
characteristic of a fluorescent substance (when a drive cycle of a
liquid crystal display device and a backlight is 60 cycle, and one
frame period is 16.7 msec, the persistence time of a G fluorescent
substance is about 8 msec which can not be neglected). The duty
driving method shown in FIG. 37 or 38 is adopted, and immediately
after driving with a large current, in order to cancel the
persistence of the fluorescent substance, the current is greatly
lowered, and then, the current is smoothly increased.
[0305] According to this example, the conventional normal direct
type backlight structure is used as it is, and the scan driving
without degradation of the motion picture quality can be performed,
and further, light quantities of many lamps can be mixed, and
accordingly, even if relatively large color irregularity and
brightness irregularity exist in the cold cathode fluorescent
lamps, those are made uniform and can be made not to be visually
recognized. Further, since it is also possible to make color
irregularity and brightness irregularity due to degradation unable
to be visually recognized, the lifetime of the display device can
be made long.
[0306] As a comparative example, FIGS. 45A and 45B and FIG. 46 show
a conventional direct type backlight unit structure and duty
driving. In a backlight 74 shown in FIG. 45A, partitions 77 are
respectively disposed between respective cold cathode fluorescent
lamps 76a to 761. Then, at the time of the duty driving, as shown
in FIG. 45B, current is sequentially supplied to the cold cathode
fluorescent lamps 76a to 761 and they are individually turned
on/off one by one. FIG. 46 shows a result obtained when the
conventional duty driving is performed to the backlight unit 74.
The horizontal axis and the vertical axis of FIG. 46 are the same
as FIG. 43B. From FIG. 46, it is understood that the motion picture
blur and the tailing phenomenon do not occur, however, it is
understood that since only a part (in the drawing, positions 114 to
140 and their vicinities) is in a lighting state in the whole frame
position, a desired brightness is not obtained.
Example 4-5
[0307] FIG. 47 shows a backlight unit 75' of example 5. This
example shows the backlight unit 75' which includes the backlight
unit 75 shown in FIG. 43A or the conventional backlight unit having
incomplete partitions formed between the respective light-emitting
areas and in which a sidelight type backlight unit is disposed
above a diffused plate 78 of a light emission opening. In the
sidelight type backlight unit, cold cathode fluorescent lamps 79
which are always turned on and are for uniform illumination are
disposed at both ends of a prism light guide plate 80. Also by this
structure, the same effect as the example 3 can be obtained.
Example 4-6
[0308] FIG. 48 shows a backlight unit 130 of example 6. The
backlight unit 130 of this example includes two light guide plates
100 and 100' which are laminated and disposed. The light guide
plates 100 and 100' include four light-emitting areas B1, B2, A1
and A2. A cold cathode fluorescent lamp 102a is disposed at one
side end face of the lower light guide plate 100 in the drawing.
Besides, a cold cathode fluorescent lamp 102b is disposed at the
other side end face of the light guide plate 100. The light guide
plate 100 includes a light guide area for guiding light from the
cold cathode fluorescent lamps 102a and 102b. In the light guide
plate 100 of the light-emitting area B1, an opposite surface 114 is
inclined with respect to a light emission surface 112 so that the
thickness at the side of the cold cathode fluorescent lamp 102a is
thin and the thickness at the side of the cold cathode fluorescent
lamp 102b is thick, and is formed into a wedge shape. Besides, in
the light guide plate 100 of the light-emitting area A1, an
opposite surface 114 is inclined with respect to the light emission
surface 112 so that the thickness at the side of the cold cathode
fluorescent lamp 102a is thick, and the thickness at the side of
the cold cathode fluorescent lamp 102b is thin, and is formed into
a wedge shape. Scattering layers 116 as light scattering elements
are formed on the opposite surfaces 114 of the light-emitting areas
A1 and B1. The light guide plate 100 includes the light guide area
for guiding the light from the cold cathode fluorescent lamps 102a
and 102b.
[0309] A cold cathode fluorescent lamp 102a' is disposed at one
side end face of the light guide plate 100' laminated and disposed
at the liquid crystal display panel 2 side of the light guide plate
100. Besides, a cold cathode fluorescent lamp 102b' is disposed at
the other side end face of the light guide plate 100'. The light
guide plate 100' includes a light guide area for guiding light from
the cold cathode fluorescent lamps 102a' and 102b'. In the light
guide plate 100' of the light-emitting area B2, an opposite surface
114 is inclined with respect to a light emission surface 112 so
that the thickness at the side of the cold cathode fluorescent lamp
102a' is thin, and the thickness at the side of the cold cathode
fluorescent lamp 102b' is thick, and is formed into a wedge shape.
Besides, in the light guide plate 100' of the light-emitting area
A2, an opposite surface 114 is inclined with respect to the light
emission surface 112 so that the thickness at the side of the cold
cathode fluorescent lamp 102a' is thick, and the thickness at the
side of the cold cathode fluorescent lamp 102b' is thin, and is
formed into a wedge shape. Scattering layers 116 as light
scattering elements are formed on the opposite surfaces 116 of the
areas A2 and B2.
[0310] In the light-emitting area B1 of the light guide plate 100,
the light guided from the side of the cold cathode fluorescent lamp
102b is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102b is not kept being guided in the
light-emitting area B1, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102a to the
light-emitting area B1 is scattered by the scattering layer 116
when it is reflected at the opposite surface, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a to the
light-emitting area B1 is kept being guided in the light-emitting
area B1, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B1 of the light guide
plate 100 has a relation of (extracted light quantity from the side
of the cold cathode fluorescent lamp 102b/guided light quantity
from the side of the cold cathode fluorescent lamp
102b)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102a/guided light quantity from the side
of the cold cathode fluorescent lamp 102a).
[0311] In the light-emitting area A1 of the light guide plate 100,
light guided from the side of the cold cathode fluorescent lamp
102a is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102 is not kept being guided in the
light-emitting area A1, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102b to the
light-emitting area A1 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b to the
light-emitting area A1 is kept being guided in the light-emitting
area A1, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area A1 of the light guide
plate 100 has a relation of (extracted light quantity from the side
of the cold cathode fluorescent lamp 102a/guided light quantity
from the side of the cold cathode fluorescent lamp
102a)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102b/guided light quantity from the side
of the cold cathode fluorescent lamp 102b).
[0312] In the light-emitting area B2 of the light guide plate 100',
light guided from the side of the cold cathode fluorescent lamp
102b' is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102b' is not kept being guided in the
light-emitting area B2, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102a' to the
light-emitting area B2 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a' to the
light-emitting area B2 is kept being guided in the light-emitting
area B2, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B2 of the light guide
plate 100' has a relation of (extracted light quantity from the
side of the cold cathode fluorescent lamp 102b'/guided light
quantity from the side of the cold cathode fluorescent lamp
102b')>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102a'/guided light quantity from the side
of the cold cathode fluorescent lamp 102a').
[0313] In the light-emitting area A2 of the light guide plate 100',
light guided from the side of the cold cathode fluorescent lamp
102a' is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102a' is not kept being guided in the
light-emitting area A2, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102b' to the
light-emitting area A2 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b' to the
light-emitting area A2 is kept being guided in the light-emitting
area A2, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B2 of the light guide
plate 100' has a relation of (extracted light quantity from the
side of the cold cathode fluorescent lamp 102a'/guided light
quantity from the side of the cold cathode fluorescent lamp
102a')>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102b'/guided light quantity from the side
of the cold cathode fluorescent lamp 102b').
[0314] The light-emitting areas B2 and A2 of the light guide plate
100 are non-light-extraction areas in which both the light from the
cold cathode fluorescent lamp 102a and the light from the cold
cathode fluorescent lamp 102b are hardly extracted. Besides, the
light-emitting areas B1 and A1 of the light guide plate 100' are
non-light-extraction areas in which both the light from the cold
cathode fluorescent lamp 102a' and the light from the cold cathode
fluorescent lamp 102b' are hardly extracted.
[0315] As stated above, in the light-emitting area A1 of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B1, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted. In the light-emitting area
A2 of the light guide plate 100', the light guided from the side of
the cold cathode fluorescent lamp 102a' is more extracted, and in
the light-emitting area B2, the light guided from the side of the
cold cathode fluorescent lamp 102b' is more extracted. Besides,
when the light guide plates 100 and 100' are laminated and
disposed, the light is almost uniformly extracted in all the
light-emitting areas B1, A1, B2 and A2.
[0316] A sidelight type backlight unit is further disposed on the
above-described backlight unit. In the sidelight type backlight
unit, cold cathode fluorescent lamps 79 which are always turned on
and are for uniform illumination, are disposed at both ends of a
prism light guide plate 80. Also in this structure, the same effect
as the example 3 can be obtained.
Example 4-7
[0317] FIG. 49 shows a backlight structure of example 7 of this
embodiment. This example also uses the TFT-LCD 1 according to the
first embodiment shown in FIG. 1, and FIG. 49 shows a state in
which a sidelight type backlight unit 82 is viewed from the side of
light emission openings of first to fourth light-emitting areas 25
to 28. In the sidelight type backlight unit 82, LEDs
(Light-Emitting Diode) (84a, 84b), (85a, 85b), (86a, 86b) and (87a,
87b) are disposed at both sides of light guide plates 83 for the
respective light-emitting areas 25 to 28. It is the similar as the
illumination device 24 shown in FIG. 1. Also when the duty driving
of this embodiment is applied to the backlight unit of the
structure shown in FIG. 49, the effect equivalent to the above
example can be obtained.
[0318] FIG. 50 shows current dependency of light emission
efficiency of an LED. The horizontal axis indicates current
supplied to the LED, and the vertical axis indicates light emission
efficiency (a.u.). FIG. 51 shows current dependency of light
emission quantity of an LED. The horizontal axis indicates current
supplied to the LED, and the vertical axis indicates light emission
quantity (a.u.). In both the drawings, a curved line connecting
rhombic marks indicates a characteristic of an LED of Ga quaternary
system (for red), a curved line connecting black circular marks
indicates a characteristic of an LED of GaN system 1 (for blue),
and a curved line connecting white circular marks indicates a
characteristic of an LED of GaN system 2 (for green).
[0319] As shown in FIGS. 50 and 51, it is understood that in the
GaN system LED of green (G) light emission and blue (B) light
emission, the current-to-light conversion efficiency is lowered by
an increase in current similarly to the cold cathode fluorescent
lamp. In addition, with respect to current, duty ratio, electric
power, current-to-light conversion efficiency, light emission
quantity and lifetime, the LED has similar characteristics to the
cold cathode fluorescent lamp. Accordingly, almost all particulars
explained on the cold cathode fluorescent lamp as an example in the
above embodiment can be applied to the LED as well. Further, since
another discharge lamp or solid light emission element also has a
tendency to have almost similar characteristics, the above
embodiment can be applied to almost all light sources.
[0320] As described above, according to this embodiment, it is
possible to realize the display device which has high brightness,
has high current-to-light conversion efficiency, has low cost, is
light, thin, short and small, has long lifetime, is superior in
uniformity of color and brightness, and is excellent in motion
picture quality.
Fifth Embodiment
[0321] An illumination device according to a fifth embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 52 to 68. First, a basic
structure of the illumination device according to this embodiment
will be described with reference to FIGS. 52 to 56. FIG. 52 shows
the basic structure of the illumination device according to this
embodiment. As shown in FIG. 52, the illumination device of this
basic structure includes a light guide plate 100 having
substantially a plate shape and made of, for example, acryl. A
linear light source, for example, a cold cathode fluorescent lamp
102b is disposed at the upper side end face of the light guide
plate 100 in the drawing while the tube axial direction is
substantially parallel to the long side direction of the light
guide plate 100. Besides, a cold cathode fluorescent lamp 102a is
disposed at the lower end face of the light guide plate 100 in the
drawing while for example, the tube axial direction is
substantially parallel to the long side direction of the light
guide plate 100. The light guide plate 100 includes a light
emission surface 112 for emitting light, and an opposite surface
114 opposite to the light emission surface 112. Besides, the light
guide plate 100 includes four light-emitting areas A1, B1, A2 and
B2 divided substantially parallel to the tube axial direction of
the cold cathode fluorescent lamps 102a and 102b. The
light-emitting areas A1, B1, A2 and B2 of the light guide plate 100
are integrally formed, and a slit is not formed at boundaries of
the respective light-emitting areas A1, B1, A2 and B2.
[0322] The light-emitting areas A1 and A2 include light extraction
elements for mainly extracting light guided from the side of the
cold cathode fluorescent lamp 102a (or the cold cathode fluorescent
lamp 102b) to the outside of the light guide plate 110. The
light-emitting areas B1 and B2 include light extraction elements
for mainly extracting light guided from the side of the cold
cathode fluorescent lamp 102b (or the cold cathode fluorescent lamp
102a) to the outside of the light guide plate 110. The
light-emitting areas A1 and A2 (or B1 and B2) for selectively
extracting light guided from the one cold cathode fluorescent lamp
102a (or 102b) are arranged alternately with the light-emitting
areas B1 and B2 (or A1 and A2) for selectively extracting light
guided from the other cold cathode fluorescent lamp 102b (or 102a).
By this, the light-emitting areas A1 and A2 (B1 and B2) for
selectively extracting the light guided from the same cold cathode
fluorescent lamp 102a or 102b are not adjacent to each other.
[0323] The illumination device according to this basic structure is
of the sidelight type that uses the linear light source. Thus,
excellent display quality without uneven brightness can be
obtained. Besides, in the illumination device according to this
basic structure, even if the light-emitting area is divided in
parallel to the long side direction of the light guide plate 100,
the tube axial direction of the cold cathode fluorescent lamps 102a
and 102b can be disposed to be substantially parallel to the long
side direction of the light guide plate 100. Thus, the linear light
source having relatively large light emission quantity and long
length can be used, and high brightness can be obtained.
[0324] FIG. 53 is a view for explaining a first principle of a
light extraction element of the illumination device according to
this basic structure. As shown in FIG. 53, a cold cathode
fluorescent lamp 102a is disposed at one side end face (left end
face in FIG. 53) of a light guide plate 100 while for example, the
tube axial direction is substantially parallel to the long side
direction of the light guide plate 100. Besides, a cold cathode
fluorescent lamp 102b is disposed at the other side end face (right
end face in FIG. 53) of the light guide plate 100 while the tube
axial direction is substantially parallel to the long side
direction of the light guide plate 100. Lamp reflectors 110 are
disposed around the cold cathode fluorescent lamps 102a and 102b.
The light guide plate 100 includes a light emission surface 112 for
emitting light, and an opposite surface 114 opposite to the light
emission surface 112. A scattering layer 116 as a light scattering
element for scattering and reflecting light is formed on the
surface of the opposite surface 114. The scattering layer 116 is
made of, for example, resin in which beads or the like are mixed,
and is formed to have a specified area and gradation. Besides, the
light guide plate 100 includes two light-emitting areas A and B
divided substantially in parallel to the tube axial direction of
the cold cathode fluorescent lamps 102a and 102b. The
light-emitting area B is disposed at the side of the cold cathode
fluorescent lamp 102a, and the light-emitting area A is disposed at
the side of the cold cathode fluorescent lamp 102b. The
light-emitting areas A and B of the light guide plate 100 are
integrally formed, and a slit is not formed at the boundary of the
respective light-emitting areas A and B. The light guide plate 100
includes a light guide area for guiding the lights from the cold
cathode fluorescent lamps 102a and 102b.
[0325] The light guide plate 100 of the light-emitting area A is
formed into such a wedge shape that the thickness at a side end
where the cold cathode fluorescent lamp 102b is disposed is thin,
and the thickness at the center is thick. The light guide plate 100
of the light-emitting area B is formed into such a wedge shape that
the thickness at the other side end where the cold cathode
fluorescent lamp 102a is disposed is thin, and the thickness at the
center is thick. The wedge shape of the light guide plate 100,
together with the light scattering element, functions as the light
extraction element.
[0326] In the light-emitting area B, light guided through the light
guide plate 100 from the side of the cold cathode fluorescent lamp
102a is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114. However, the light is concentrated by
the wedge shape of the light guide plate 100 each time it is
reflected, and the incident angle with respect to the light
emission surface 112 becomes large. Thus, the light guided from the
side of the cold cathode fluorescent lamp 102a is kept being guided
in the light-emitting area B like a light beam. L1, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, the light guided from the side
of the cold cathode fluorescent lamp 102b is not kept being guided
in the light-emitting area B, and is emitted to the outside of the
light guide plate 100 like a light beam L4. That is, the
light-emitting area B has a relation of (extracted light quantity
from the side of the cold cathode fluorescent lamp 102b/guided
light quantity from the side of the cold cathode fluorescent lamp
102b)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102a/guided light quantity from the side
of the cold cathode fluorescent lamp 102a).
[0327] In the light-emitting area A, light guided through the light
guide plate 100 from the side of the cold cathode fluorescent lamp
102b is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114. However, the light is concentrated by
the wedge shape of the light guide plate 100 each time it is
reflected, and the incident angle with respect to the light
emission surface 112 becomes large. Thus, the light guided from the
side of the cold cathode fluorescent lamp 102b is kept being guided
in the light-emitting area A like a light beam. L3, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102a is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, the light guided from the side
of the cold cathode fluorescent lamp 102a is not kept being guided
in the light-emitting area A, and is emitted to the outside of the
light guide plate 100 like a light beam L2. That is, the
light-emitting area A has a relation of (extracted light quantity
from the side of the cold cathode fluorescent lamp 102a/guided
light quantity from the side of the cold cathode fluorescent lamp
102a)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102b/guided light quantity from the side
of the cold cathode fluorescent lamp 102b).
[0328] As stated above, in the light-emitting area A of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted. Incidentally, it is
appropriate that the interface of the scattering layer 116 at the
air side is formed to be flat (so-called bulk type scatter
structure) rather than formed to be uneven. By this, it is possible
to greatly reduce the ratio at which the light from the side of the
cold cathode fluorescent lamp 102a (the side of the cold cathode
fluorescent lamp 102b) is emitted from the interface of the
scattering layer 116 of the light-emitting area B (light-emitting
area A) to the side of the air layer.
[0329] FIG. 54 is a view for explaining a second principle of a
light extraction element of the illumination device according to
this basic structure. As shown in FIG. 54, a light guide plate 100
includes two light-emitting areas A and B divided substantially in
parallel to the tube axial direction of cold cathode fluorescent
lamps 102a and 102b. The light-emitting area B is disposed at the
side of the cold cathode fluorescent lamp 102a, and the
light-emitting area A is disposed at the side of the cold cathode
fluorescent lamp 102b. The light-emitting areas A and B of the
light guide plate 100 are integrally formed, and a slit is not
formed at the boundary of the respective light-emitting areas A and
B. An opposite surface 114 of the light guide plate 100 is formed
into a prism shape. The prism shape functions as the light
extraction element for extracting light.
[0330] The opposite surface 114 of the light-emitting area B has
such a prism shape that light from the side of the cold cathode
fluorescent lamp 102a is not incident on a prism surface 118, but
is guided to the light-emitting area A as it is like a light beam
L1. The prism surface 118 is formed to have an inclination angle
of, for example, 40.degree. to 45.degree. with respect to a light
emission surface 112. On the other hand, light from the side of the
cold cathode fluorescent lamp 102b is incident on the prism surface
118 at a certain probability. The light incident on the prism
surface comes not to satisfy a total reflection condition and is
emitted to the outside of the light guide plate 100 like a light
beam L4 by reflection or refraction.
[0331] The opposite surface 114 of the light-emitting area A has
such a prism shape that light from the side of the cold cathode
fluorescent lamp 102b is not incident on a prism surface 119, but
is guided to the light-emitting area B as it is like a light beam
L3. The prism surface 119 is formed to have an inclination angle
of, for example, 40.degree. to 45.degree. with respect to the light
emission surface 112. On the other hand, light from the side of the
cold cathode fluorescent lamp 102a is incident on the prism surface
119 at a certain probability. The light incident on the prism
surface 119 comes not to satisfy the total reflection condition and
is emitted to the outside of the light guide plate 100 like a light
beam L2 by reflection or refraction.
[0332] As stated above, in the light-emitting area A of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted.
[0333] FIG. 55 is a view for explaining a third principle of a
light extraction element of the illumination device according to
this basic structure. As shown in FIG. 55, a scattering layer 116
as a light scattering element for scattering and reflecting light
is formed on the surface of an opposite surface 114 of a light
guide plate 100. The light guide plate 100 includes two
light-emitting areas A and B divided substantially in parallel to
the tube axial direction of cold cathode fluorescent lamps 102a and
102b. The light-emitting area A is disposed at the side of the cold
cathode fluorescent lamp 102a, and the light-emitting area B is
disposed at the side of the cold cathode fluorescent lamp 102b.
[0334] The light guide plate 100 of the light-emitting area A is
formed into such a wedge shape that the thickness at the side of a
side end where the cold cathode fluorescent lamp 102a is disposed
is thick, and the thickness at the center is thin. Similarly, the
light guide plate 100 of the light-emitting area B is formed into
such a wedge shape that the thickness at the side of a side end
where the cold cathode fluorescent lamp 102b is disposed is thick,
and the thickness at the center is thin. The light-emitting areas A
and B of the light guide plate 100 are integrally formed and a slit
is not formed at the boundary of the respective light-emitting
areas A and B. Besides, the light-emitting areas A and B are not
completely separated. The wedge shape of the light guide plate 100,
together with the light scattering element, functions as the light
extraction element.
[0335] In the light-emitting area A, light guided from the side of
the cold cathode fluorescent lamp 102a is scattered by the
scattering layer 116 when it is reflected at the opposite surface
114, and the incident angle with respect to a light emission
surface 112 becomes small by the wedge shape of the light guide
plate 100 each time it is reflected at the opposite surface 114.
Thus, most of the light guided from the side of the cold cathode
fluorescent lamp 102a is not kept being guided in the
light-emitting area A and is emitted to the outside of the light
guide plate 100. On the other hand, although the light guided to
the light-emitting area B from the side of the cold cathode
fluorescent lamp 102a is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided to
the light-emitting area B from the side of the cold cathode
fluorescent lamp 102a is kept being guided in the light-emitting
area B, and is not emitted to the outside of the light guide plate
100 much.
[0336] In the light-emitting area B, light guided from the side of
the cold cathode fluorescent lamp 102b is scattered by the
scattering layer 116 when it is reflected at the opposite surface
114, and the incident angle with respect to the light emission
surface 112 becomes small by the wedge shape of the light guide
plate 100 each time it is reflected at the opposite surface 114.
Thus, most of the light guided from the side of the cold cathode
fluorescent lamp 102b is not kept being guided in the
light-emitting area B and is emitted to the outside of the light
guide plate 100. On the other hand, although the light guided to
the light-emitting area A from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100, and
the incident angle with respect to the light emission surface 112
becomes large. Thus, the light guided to the light-emitting area A
from the side of the cold cathode fluorescent lamp 102b is kept
being guided in the light-emitting area A, and is not emitted to
the outside of the light guide plate 100 much.
[0337] As stated above, in the light-emitting area A of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted.
[0338] FIG. 56 is a view for explaining a fourth principle of a
light extraction element of the illumination device according to
this basic structure. As shown in FIG. 56, a light guide plate 100
includes two light-emitting areas A and B divided substantially in
parallel to the tube axial direction of cold cathode fluorescent
lamps 102a and 102b. The light-emitting area A is disposed at the
side of the cold cathode fluorescent lamp 102a, and the
light-emitting area B is disposed at the side of the cold cathode
fluorescent lamp 102b. An opposite surface 114 of the light guide
plate 100 is formed into a prism shape. The prism shape functions
as a light extraction element for extracting light. The
light-emitting areas A and B of the light guide plate 100 are
integrally formed, and a slit is not formed at the boundary of the
respective light-emitting areas A and B.
[0339] The opposite surface 114 of the light-emitting area A has
such a prism shape that light from the side of the cold cathode
fluorescent lamp 102a is incident on a prism surface 119 at a
certain probability, and light from the side of the cold cathode
fluorescent lamp 102b is not incident on the prism surface 119. The
prism surface 119 is formed to have an inclination angle of, for
example, 40.degree. to 45.degree. with respect to the light
emission surface 112. The light incident on the prism surface 119
comes not to satisfy the total reflection condition and is emitted
to the outside of the light guide plate 100 by reflection or
refraction.
[0340] The opposite surface 114 of the light-emitting area B has
such a prism shape that light from the side of the cold cathode
fluorescent lamp 102b is incident on a prism surface 118 at a
certain probability, and light from the side of the cold cathode
fluorescent lamp 102a is not incident on the prism surface 118. The
prism surface 118 is formed to have an inclination angle of, for
example, 40.degree. to 45.degree. with respect to the light
emission surface 112. The light incident on the prism surface 118
comes not to satisfy the total reflection condition and is emitted
to the outside of the light guide plate 100 by reflection or
refraction.
[0341] As stated above, in the light-emitting area A of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted.
[0342] Hereinafter, an illumination device according to this
embodiment and a liquid crystal display device using the same will
be described specifically with reference to examples 5-1 to
5-6.
Example 5-1
[0343] An illumination device according to example 5-1 of this
embodiment and a liquid crystal display device using the same will
be described with reference to FIGS. 57 to 61. FIG. 57 is a block
diagram showing a rough structure of the liquid crystal display
device according to this example. As shown in FIG. 57, the liquid
crystal display device includes a backlight unit 130, a control
circuit 16, and a driving circuit composed of a gate driver 12 and
a data driver 14. The backlight unit 130 includes a light source
control part (light source driving circuit) 132. The light source
control part 132 is connected to the control circuit 16. A clock
CLK outputted from a system side such as a PC, a data enable signal
Enab, gradation data Data and the like are inputted to the control
circuit 16. Besides, the control circuit 16 includes a frame memory
(not shown) for storing image signals of one frame. The gate driver
12 and the data driver 14 are connected to the control circuit 16.
The gate driver 12 includes, for example, a shift register,
receives a latch pulse signal LP from a gate driver control part in
the control circuit 16, and sequentially outputs a gate pulse to
lines starting from a display start line to perform line sequential
driving.
[0344] The liquid crystal display device includes N gate bus lines
6-1 to 6-N (only four lines are shown in FIG. 57) in a display area
134. The respective gate bus lines 6-1 to 6-N are connected to the
gate driver 12. The display area 134 is divided into four areas B1,
A1, B2 and A2 extending in parallel to the gate bus line 6. The
areas B1, A1, B2 and A2 are respectively illuminated by the
corresponding light-emitting areas B1, A1, B2 and A2 of the
backlight unit 130. The gate bus lines 6-1 to 6-(N/4) are disposed
in the area B1. The gate bus lines 6-(N/4+1) to 6-(N/2) are
disposed in the area A1. The gate bus lines 6-(N/2+1) to
6-(3.times.N/4) are disposed in the area B2. The gate bus lines
6-(3.times.N/4+1) to 6-N are disposed in the area A2.
[0345] FIG. 58 shows a sectional structure of the liquid crystal
display device according to this example. FIG. 59 shows a sectional
structure of the backlight unit 130 of the illumination device
according to this example. As shown in FIGS. 58 and 59, the liquid
crystal display device includes a transmission type LCD panel 2 and
the backlight unit 130. The backlight unit 130 includes a
substantially plate-shaped light guide plate 100.
[0346] A cold cathode fluorescent lamp 102a of a linear light
source is disposed at one end face (left end face in FIGS. 58 and
59) of the light guide plate 100 while for example, the tube axial
direction is substantially parallel to the long side direction of
the light guide plate 100. Besides, a cold cathode fluorescent lamp
102b is disposed at the other end face (right end face in FIGS. 58
and 59) of the light guide plate 100 while for example, the tube
axial direction is substantially parallel to the long side
direction of the light guide plate 100. Lamp reflectors 110 are
disposed around the cold cathode fluorescent lamps 102a and 102b.
The light guide plate 100 includes a light emission surface 112 for
emitting light and an opposite surface 114 opposite to the light
emission surface 112. A scattering layer 116 as a light scattering
element is formed on the opposite surface 114. Besides, the light
guide plate 100 includes four light-emitting areas B1, A1, B2 and
A2 divided substantially in parallel to the tube axial direction of
the cold cathode fluorescent lamps 102a and 102b. The
light-emitting area B1 is disposed at the side of the cold cathode
fluorescent lamp 102a, and the light-emitting area A1 is disposed
to be adjacent to the light-emitting area B1. The light-emitting
area B2 is disposed to be adjacent to the light-emitting area A1,
and the light-emitting area A2 is disposed at the side of the cold
cathode fluorescent lamp 102b. The light-emitting areas B1, A1, B2
and A2 are integrally formed, and a slit is not formed at
boundaries of the respective light-emitting areas B1, A1, B2 and
A2.
[0347] The opposite surface 114 of the light-emitting areas B1 and
B2 has such a prism shape that light from the side of the cold
cathode fluorescent lamp 102a is not incident on a prism surface
118, but is guided to the side of the cold cathode fluorescent lamp
102b as it is. The prism surface 118 is formed to have an
inclination angle of, for example, 40.degree. to 45.degree. with
respect to the light emission surface 112. On the other hand, light
from the side of the cold cathode fluorescent lamp 102b is incident
on the prism surface 118 at a certain probability. The light
incident on the prism surface 118 comes not to satisfy the total
reflection condition and is emitted to the outside of the light
guide plate 100 by reflection or refraction.
[0348] The opposite surface 114 of the light-emitting areas A1 and
A2 has such a prism shape that light from the side of the cold
cathode fluorescent lamp 102b is not incident on a prism surface
119, but is guided to the side of the cold cathode fluorescent lamp
102b as it is. The prism surface 119 is formed to have an
inclination angle of, for example, 40.degree. to 45.degree. with
respect to the light emission surface 112. On the other hand, light
from the side of the cold cathode fluorescent lamp 102a is incident
on the prism surface 119 at a certain probability. The light
incident on the prism surface 119 comes not to satisfy the total
reflection condition and is emitted to the outside of the light
guide plate 100 by reflection or refraction.
[0349] As stated above, in the light-emitting areas A1 and A2 of
the light guide plate 100, the light guided from the side of the
cold cathode fluorescent lamp 102a is more extracted, and in the
light-emitting areas B1 and B2, the light guided from the side of
the cold cathode fluorescent lamp 102b is more extracted. Besides,
in the light guide plate 100, light can be extract almost uniformly
in all the light-emitting areas B1, A1, B2 and A2.
[0350] A light distribution sheet group 136 including plural light
distribution sheets, for improving a light distribution
characteristic is disposed between the LCD panel 2 and the light
guide plate 100. Besides, a reflection scattering sheet 138 for
scattering and reflecting light is disposed at the side of the
opposite surface 114 of the light guide plate 100.
[0351] FIG. 60 shows a driving method of the illumination device
according to this example and the liquid crystal display device
using the same. The horizontal axis direction indicates time, and
the vertical axis direction indicates a writing state
(writing/non-writing) of gradation data and a blinking state
(ON/OFF) of the illumination device. A waveform "a" indicates a
writing state of gradation data in the area B1, and a waveform "b"
indicates a writing state of gradation data in the area A1. A
waveform "c" indicates a writing state of gradation data in the
area B2, and a waveform "d" indicates a writing state of gradation
data in the area A2. Besides, a waveform "e" indicates a blinking
state of the cold cathode fluorescent lamp 102a, and a waveform "f"
indicates a blinking state of the cold cathode fluorescent lamp
102b. As shown in FIG. 60, the light source control part 132
synchronizes with the latch pulse signal LP and causes the cold
cathode fluorescent lamps 102a and 102b to emit light for a
specified time at a blinking frequency equal to a frame frequency
(for example, 60 Hz). Besides, the light source control part 132
causes a timing at which light emission brightness of the cold
cathode fluorescent lamp 102a is made maximum to be different from
a timing at which light emission brightness of the cold cathode
fluorescent lamp 102b is made maximum by about 8.4 msec (1/2
period).
[0352] The gradation data is written into the pixels of the areas
B1 and B2 substantially at the same timing. The liquid crystal
display device of this example is of the multi-scan type, and the
gate driver 12 outputs the gate pulse GP in the order of the gate
bus lines 6-1, 6-(N/2+1), 6-2, 6-(N/2+2), . . . . That is, the gate
bus lines 6 of the areas B1 and B2 are alternately scanned.
Besides, after the 1/2 period has passed since the gate pulse GP
was outputted to the gate bus line 6-1, the gate pulse GP is
outputted to the gate bus line 6-(N/4+1), and thereafter, scanning
is performed in the order of the gate bus lines 6-(3.times.N/4+1),
6-(N/4+2), 12-(3.times.N/4+2), . . . .
[0353] After a specified time has passed since the gradation data
were written into the pixels of the areas B1 and B2, the cold
cathode fluorescent lamp 102b for causing the light-emitting areas
B1 and B2 to emit light is turned on. Besides, after the cold
cathode fluorescent lamp 102b is turned off, the gradation data are
written into the pixels of the areas B1 and B2. Similarly, after a
specified time has passed since the gradation data were written
into the pixels of the areas A1 and A2, the cold cathode
fluorescent lamp 102a for causing the light-emitting areas A1 and
A2 to emit light is turned on. Besides, after the cold cathode
fluorescent lamp 102a is turned off, the gradation data are written
into the pixels of the areas A1 and A2. As stated above, the cold
cathode fluorescent lamp at the side of the areas in which the
gradation data are written is turned off. In the liquid crystal
display device, since it takes a time of several msec to several
tens msec until a liquid crystal molecule is inclined at a
specified inclination angle from the writing of the gradation data
into the pixel, when a time from the writing of the gradation data
to the lighting of the cold cathode fluorescent lamp is secured to
the extent possible, more excellent display quality of a motion
picture can be obtained. Thus, in this example, immediately after
the cold cathode fluorescent lamp 102a (102b) is turned off, the
writing (rewriting) of gradation data into the areas A1, A2 (B1,
B2) is started, and the time from the end of the writing of the
gradation data into the areas A1 and A2 (B1 and B2) to the lighting
of the cold cathode fluorescent lamp 102a (102b) is secured as the
response time of the liquid crystal molecule.
[0354] In this example, although the lighting times of the cold
cathode fluorescent lamps 102a and 102b are made equal to each
other, the lighting times of the cold cathode fluorescent lamps
102a and 102b may be made different from each other. Besides, in
this example, although the cold cathode fluorescent lamps 102a and
102b are turned on/off at the specified frequency, the light
emission brightnesses of the cold cathode fluorescent lamps 102a
and 102b may be changed at a specified frequency.
[0355] The illumination device according to this example is of the
sidelight type using the cold cathode fluorescent lamps 102a and
102b as the linear light sources. Thus, the excellent display
quality without uneven brightness can be obtained. Besides, in the
illumination device according to this example, even if the
light-emitting area is divided in parallel to the long side
direction of the light guide plate 100, the cold cathode
fluorescent lamps 102a and 102b can be disposed while the tube
axial direction is made substantially parallel to the long side
direction of the light guide plate 100. Thus, the linear light
source having a relatively large light emission quantity and a long
length can be used. Accordingly, the scan type illumination device
having a high brightness can be realized, and also when a motion
picture is displayed, excellent display quality without contour
blurring can be obtained.
[0356] FIG. 61 is a block diagram showing a modified example of the
structure of the liquid crystal display device according to this
example. As shown in FIG. 61, in this modified example, a gate
driver 12 for driving gate bus lines 6-1 to 6-(N/2) of areas B1 and
A1 and a gate driver 12' for driving gate bus lines 6-(N/2+1) to
6-N of areas B2 and A2 are provided to be independent of each
other. Both the gate drivers 12 and 12' are connected to a control
circuit 16. The gate driver 12 synchronizes with a latch pulse LP
inputted from the control circuit 16 to output a gate pulse GP to
the gate bus line 6-1, and at the same time, the gate driver 12'
outputs a gate pulse GP to the gate bus line 6-(N/2+1). In this
way, in this modified example, the gate driver 12 scans in the
order of the gate bus lines 6-1, 6-2, . . . , 6-(N/2), and at the
same time, the gate driver 12' can scan in the order of the gate
bus lines 6-(N/2+1), 6-(N/2+2), . . . , 6-N. Also by this modified
example, the same effect as the above example can be obtained.
Example 5-2
[0357] First, an illumination device according to example 5-2 of
this embodiment will be described with reference to FIG. 62. FIG.
62 shows a sectional structure of the illumination device according
to this example. As shown in FIG. 62, a light guide plate 100
includes four light-emitting areas B1, A1, B2 and A2 divided
substantially in parallel to the tube axial direction of cold
cathode fluorescent lamps 102a and 102b. The light-emitting area B1
is disposed at the side of the cold cathode fluorescent lamp 102a,
and the light-emitting area A1 is disposed to be adjacent to the
light-emitting area B1. The light-emitting area B2 is disposed to
be adjacent to the light-emitting area A1, and the light-emitting
area A2 is disposed at the side of the cold cathode fluorescent
lamp 102b. The light-emitting areas B1, A1, B2 and A2 of the light
guide plate 100 are integrally formed, and a slit is not formed at
boundaries of the respective light-emitting areas B1, A1, B2 and
A2.
[0358] In the light guide plate 100, an opposite surface 114 is
inclined at a specified inclination angle with respect to a light
emission surface 112, and is formed into different wedge shapes for
the respective areas. The light guide plate 100 of the
light-emitting areas A1 and A2 is formed into such a wedge shape
that the thickness at the side of a side end where the cold cathode
fluorescent lamp 102a is disposed is thick, and the thickness at
the side of a side end where the cold cathode fluorescent lamp 102b
is disposed is thin. The light guide plate 100 of the
light-emitting areas B1 and B2 is formed into such a wedge shape
that the thickness at the side of the side end where the cold
cathode fluorescent lamp 102a is disposed is thin, and the
thickness at the side of the side end where the cold cathode
fluorescent lamp 102b is disposed is thick. For example, the
inclination angles of the opposite surface 114 of the areas A1 and
B2 are small as compared with the inclination angles of the
opposite surface 114 of the areas B1 and A2. The wedge shapes of
the light guide plate 100, together with a light scattering
element, function as light extraction elements.
[0359] In the light-emitting areas B1 and B2, light guided through
the light guide plate 100 from the side of the cold cathode
fluorescent lamp 102a is scattered by a scattering layer 116 when
it is reflected at the opposite surface 114. However, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a is kept
being guided in the light-emitting areas B1 and B2, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, part of the light guided from
the side of the cold cathode fluorescent lamp 102b is not kept
being guided in the light-emitting areas B1 and B2, and is emitted
to the outside of the light guide plate 100.
[0360] In the light-emitting areas A1 and A2, light guided through
the light guide plate 100 from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114. However, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b is kept
being guided in the light-emitting areas A1 and A2, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102a is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, part of the light guided from
the side of the cold cathode fluorescent lamp 102a is not kept
being guided in the light-emitting areas A1 and A2, and is emitted
to the outside of the light guide plate 100.
[0361] As stated above, in the light-emitting areas A1 and A2, the
light guided from the side of the cold cathode fluorescent lamp
102a is more extracted, and in the light-emitting areas B1 and B2,
the light guided from the side of the cold cathode fluorescent lamp
102b is more extracted. Besides, in the light guide plate 100,
light can be extracted almost uniformly in all the light-emitting
areas B1, A1, B2 and A2. According to this example, the same effect
as the example 5-1 can be obtained.
Example 5-3
[0362] Next, an illumination device according to example 5-3 of
this embodiment will be described with reference to FIG. 63. FIG.
63 shows a sectional structure of the illumination device according
to this example. As shown in FIG. 63, a light guide plate 100
includes four light-emitting areas A1, B1, A2 and B2 divided
substantially in parallel to the tube axial direction of cold
cathode fluorescent lamps 102a and 102b. The light-emitting area A1
is disposed at the side of the cold cathode fluorescent lamp 102a,
and the light-emitting area B1 is disposed to be adjacent to the
light-emitting area A1. The light-emitting area A2 is disposed to
be adjacent to the light-emitting area B1, and the light-emitting
area B2 is disposed at the side of the cold cathode fluorescent
lamp 102b. The light-emitting areas A1, B1, A2 and B2 of the light
guide plate 100 are integrally formed, and a slit is not formed at
boundaries of the respective light-emitting areas A1, B1, A2 and
B2.
[0363] In the light guide plate 100, an opposite surface 114 is
inclined at specified inclination angles with respect to a light
emission surface 112, and is formed into different wedge shapes for
the respective areas. The light guide plate 100 of the
light-emitting areas A1 and A2 is formed into such a wedge shape
that the thickness at the side of a side end where the cold cathode
fluorescent lamp 102a is disposed is thick, and the thickness at
the side of a side end where the cold cathode fluorescent lamp 102b
is disposed is thin. The light guide plate 100 of the
light-emitting areas B1 and B2 is formed into such a wedge shape
that the thickness at the side of the side end where the cold
cathode fluorescent lamp 102a is disposed is thin, and the
thickness at the side of the side end where the cold cathode
fluorescent lamp 102b is disposed is thick. For example, the
inclination angles of the opposite surface 114 of the areas A2 and
B1 are small as compared with the inclination angles of the
opposite surface 114 of the areas A1 and B2. The wedge shapes of
the light guide plate 100, together with a light scattering
element, function as light extraction elements.
[0364] In the light-emitting areas B1 and B2, light guided through
the light guide plate 100 from the side of the cold cathode
fluorescent lamp 102a is scattered by a scattering layer 116 when
it is reflected at the opposite surface 114. However, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a is kept
being guided in the light-emitting areas B1 and B2, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, part of the light guided from
the side of the cold cathode fluorescent lamp 102b is not kept
being guided in the light-emitting areas B1 and B2, and is emitted
to the outside of the light guide plate 100.
[0365] In the light-emitting areas A1 and A2, light guided through
the light guide plate 100 from the side of the cold cathode
fluorescent lamp 102b is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114. However, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b is kept
being guided in the light-emitting areas A1 and A2, and is not
emitted to the outside of the light guide plate 100 much. On the
other hand, light guided from the side of the cold cathode
fluorescent lamp 102a is scattered by the scattering layer 116 when
it is reflected at the opposite surface 114, and the incident angle
with respect to the light emission surface 112 becomes small by the
wedge shape of the light guide plate 100 each time it is reflected
at the opposite surface 114. Thus, part of the light guided from
the side of the cold cathode fluorescent lamp 102a is not kept
being guided in the light-emitting areas A1 and A2, and is emitted
to the outside of the light guide plate 100.
[0366] As stated above, in the light-emitting areas A1 and A2 of
the light guide plate 100, the light guided from the side of the
cold cathode fluorescent lamp 102a is more extracted, and in the
light-emitting areas B1 and B2, the light guided from the side of
the cold cathode fluorescent lamp 102b is more extracted. Besides,
in the light guide plate 100, light can be extracted almost
uniformly in all the light-emitting areas B1, A1, B2 and A2.
[0367] According to this example, the same effect as the example
5-1 can be obtained. Besides, in the liquid crystal display device
using the backlight unit 130 according to this example, the timing
of brightness modulation of the cold cathode fluorescent lamps 102a
and 102b is made opposite to the timing of brightness modulation of
the example 5-1 shown in FIG. 60, so that the scan type
illumination device having high brightness can be realized, and
also when a motion picture is displayed, excellent display quality
without contour blurring can be obtained.
Example 5-4
[0368] Next, an illumination device according to example 5-4 of
this embodiment will be described with reference to FIG. 64. FIG.
64 shows a sectional structure of the illumination device according
to this example. As shown in FIG. 64, a light guide plate 100
includes four light-emitting areas A1, B1, A2 and B2 divided
substantially in parallel to the tube axial direction of cold
cathode fluorescent lamps 102a and 102b. The light-emitting area A1
is disposed at the side of the cold cathode fluorescent lamp 102a,
and the light-emitting area B1 is disposed to be adjacent to the
light-emitting area A1. The light-emitting area A2 is disposed to
be adjacent to the light-emitting area B1, and the light-emitting
area B2 is disposed at the side of the cold cathode fluorescent
lamp 102b. The light-emitting areas A1, B1, A2 and B2 of the light
guide plate 100 are integrally formed, and a slit is not formed at
boundaries of the respective light-emitting areas A1, B1, A2 and
B2. An opposite surface 114 of the light guide plate 100 is formed
into a prism shape, and the prism shape functions as a light
extraction element for extracting light.
[0369] The opposite surface 114 of the light-emitting areas B1 and
B2 has such a prism shape that light from the side of the cold
cathode fluorescent lamp 102a is not incident on the prism surface
118, but is guided to the side of the cold cathode fluorescent lamp
102b as it is. The prism surface 118 is formed to have an
inclination angle of, for example, 40.degree. to 45.degree. with
respect to the light emission surface 112. On the other hand, light
from the side of the cold cathode fluorescent lamp 102b is incident
on the prism surface 118 at a certain probability. The light
incident on the prism surface 118 comes not to satisfy the total
reflection condition and is emitted to the outside of the light
guide plate 100 by reflection or refraction.
[0370] The opposite surface 114 of the light-emitting areas A1 and
A2 has such a prism shape that light from the side of the cold
cathode fluorescent lamp 102b is not incident on a prism surface
119, but is guided to the side of the cold cathode fluorescent lamp
102b as it is. The prism surface 119 is formed to have an
inclination angle of, for example, 40.degree. to 45.degree. with
respect to the light emission surface 112. On the other hand, light
from the cold cathode fluorescent lamp 102a is incident on the
prism surface 119 at a certain probability. The light incident on
the prism surface 119 comes not to satisfy the total reflection
condition and is emitted to the outside of the light guide plate
100 by reflection or refraction.
[0371] As stated above, in the light-emitting areas A1 and A2 of
the light guide plate 100, the light guided from the side of the
cold cathode fluorescent lamp 102a is more extracted, and in the
light-emitting areas B1 and B2, the light guided from the side of
the cold cathode fluorescent lamp 102b is more extracted. Besides,
in the light guide plate 100, light can be extracted almost
uniformly in all the light-emitting areas B1, A1, B2 and A2.
According to this example, the same effect as the example 5-1 can
be obtained.
Example 5-5
[0372] Next, a liquid crystal display device according to example
5-5 of this embodiment will be described with reference to FIG. 65.
FIG. 65 shows a sectional structure of the liquid crystal display
device according to this example. As shown in FIG. 65, the liquid
crystal display device according to this example is of a front
light system, and includes a reflection type LCD panel 2 and a
front light unit 131. A light guide plate 100 of the front light
unit 131 includes four light-emitting areas B1, A1, B2 and A2
divided substantially in parallel to the tube axial direction of
cold cathode fluorescent lamps 102a and 102b. The light-emitting
area B1 is disposed at the side of the cold cathode fluorescent
lamp 102a, and the light-emitting area A1 is disposed to be
adjacent to the light-emitting area B1. The light-emitting area B2
is disposed to be adjacent to the light-emitting area A1, and the
light-emitting area A2 is disposed at the side of the cold cathode
fluorescent lamp 102b. The light-emitting areas B1, A1, B2 and A2
of the light guide plate 100 are integrally formed, and a slit is
not formed at boundaries of the respective light-emitting areas B1,
A1, B2 and A2. An opposite surface 114 of the light guide plate 100
is formed into a prism shape. The prism shape functions as a light
extraction element for extracting light.
[0373] In the front light system, it is not wise to use a
scattering layer 116 or the like as a light extraction element.
This is because scattered light by the scattering layer 116 is not
emitted in the direction vertical to the LCD panel 2, so that it
becomes a cause of low contrast and low brightness. Besides, since
light is directly emitted to an observer side as well, it becomes a
cause of stray light and low contrast, and display quality is
lowered. Accordingly, in this example, the light extraction element
is made the prism shape. Besides, the light guide plate 100 and a
polarizing plate 141 are bonded to each other, and are further
bonded to the LCD panel 2, so that interface reflection is lowered
and the display quality can be further improved.
Example 5-6
[0374] Next, an illumination device according to example 5-6 of
this embodiment and a liquid crystal display device using the same
will be described with reference to FIGS. 66 to 68. FIG. 66 shows a
sectional structure of the liquid crystal display device according
to this example. FIG. 67 shows a sectional structure of the
illumination device according to this example. As shown in FIGS. 66
and 67, a backlight unit 130 according to this example includes two
light guide plates 100 and 100' which are laminated and disposed.
The light guide plates 100 and 100' include four light-emitting
areas B1, B2, A1 and A2. A cold cathode fluorescent lamp 102a is
disposed at one side end face (left end face in FIGS. 66 and 67) of
the lower light guide plate 100 in the drawing. Besides, a cold
cathode fluorescent lamp 102b is disposed at the other side end
face (right end face in FIGS. 66 and 67) of the light guide plate
100. The light guide plate 100 includes a light guide area for
guiding light from the cold cathode fluorescent lamps 102a and
102b. In the light guide plate 100 of the light-emitting area B1,
an opposite surface 114 is inclined with respect to a light
emission surface 112 so that the thickness at the side of the cold
cathode fluorescent lamp 102a is thin and the thickness at the side
of the cold cathode fluorescent lamp 102b is thick, and is formed
into a wedge shape. Besides, in the light guide plate 100 of the
light-emitting area A1, an opposite surface 114 is inclined with
respect to the light emission surface 112 so that the thickness at
the cold cathode fluorescent lamp 102a is thick and the thickness
at the cold cathode fluorescent lamp 102b is thin, and is formed
into a wedge shape. Scattering layers 116 as light scattering
elements are formed on the opposite surfaces 114 of the
light-emitting areas A1 and B1. The light guide plate 100 includes
the light guide area for guiding light from the cold cathode
fluorescent lamps 102a and 102b.
[0375] A cold cathode fluorescent lamp 102a' is disposed at one
side end face (left end face in FIGS. 66 and 67) of the light guide
plate 100' laminated and disposed at the liquid crystal display
panel 2 side of the light guide plate 100. Besides, a cold cathode
fluorescent lamp 102b' is disposed at the other side end face
(right end face in FIGS. 66 and 67) of the light guide plate 100'.
The light guide plate 100' includes a light guide area for guiding
light from the cold cathode fluorescent lamps 102a' and 102b'. In
the light guide plate 100' of the light-emitting area B2, an
opposite surface 114 is inclined with respect to a light emission
surface 112 so that the thickness at the side of the cold cathode
fluorescent lamp 102a' is thin and the thickness at the side of the
cold cathode fluorescent lamp 102b' is thick, and is formed into a
wedge shape. Besides, in the light guide plate 100' of the
light-emitting area A2, an opposite surface 114 is inclined with
respect to the light emission surface 112 so that the thickness at
the side of the cold cathode fluorescent lamp 102a' is thick and
the thickness at the side of the cold cathode fluorescent lamp
102b' is thin, and is formed into a wedge shape. Scattering layers
116 as light scattering elements are formed on the opposite
surfaces 114 of the areas A2 and B2.
[0376] In the light-emitting area B1 of the light guide plate 100,
light guided from the side of the cold cathode fluorescent lamp
102b is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102b is not kept being guided in the
light-emitting area B1, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102a to the
light-emitting area B1 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a to the
light-emitting area B1 is kept being guided in the light-emitting
area B1, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B1 of the light guide
plate 100 has a relation of (extracted light quantity from the side
of the cold cathode fluorescent lamp 102b/guided light quantity
from the side of the cold cathode fluorescent lamp
102b)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102a/guided light quantity from the side
of the cold cathode fluorescent lamp 102a).
[0377] In the light-emitting area A1 of the light guide plate 100,
light guided from the side of the cold cathode fluorescent lamp
102a is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102 is not kept being guided in the
light-emitting area A1, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102b to the
light-emitting area A1 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b to the
light-emitting area A1 is kept being guided in the light-emitting
area A1, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area A1 of the light guide
plate 100 has a relation of (extracted light quantity from the side
of the cold cathode fluorescent lamp 102a/guided light quantity
from the side of the cold cathode fluorescent lamp
102a)>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102b/guided light quantity from the side
of the cold cathode fluorescent lamp 102b).
[0378] In the light-emitting area B2 of the light guide plate 100',
light guided from the side of the cold cathode fluorescent lamp
102b' is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102b' is not kept being guided in the
light-emitting area B2, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102a' to the
light-emitting area B2 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102a' to the
light-emitting area B2 is kept being guided in the light-emitting
area B2, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B2 of the light guide
plate 100' has a relation of (extracted light quantity from the
side of the cold cathode fluorescent lamp 102b'/guided light
quantity from the side of the cold cathode fluorescent lamp
102b')>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102a'/guided light quantity from the side
of the cold cathode fluorescent lamp 102a').
[0379] In the light-emitting area A2 of the light guide plate 100',
light guided from the side of the cold cathode fluorescent lamp
102a' is scattered by the scattering layer 116 when it is reflected
at the opposite surface 114, and the incident angle with respect to
the light emission surface 112 becomes small by the wedge shape of
the light guide plate 100 each time it is reflected at the opposite
surface 114. Thus, most of the light guided from the side of the
cold cathode fluorescent lamp 102a' is not kept being guided in the
light-emitting area A2, and is emitted to the outside of the light
guide plate 100. On the other hand, although light guided from the
side of the cold cathode fluorescent lamp 102b' to the
light-emitting area A2 is scattered by the scattering layer 116
when it is reflected at the opposite surface 114, the light is
concentrated by the wedge shape of the light guide plate 100 each
time it is reflected, and the incident angle with respect to the
light emission surface 112 becomes large. Thus, the light guided
from the side of the cold cathode fluorescent lamp 102b' to the
light-emitting area A2 is kept being guided in the light-emitting
area A2, and is not emitted to the outside of the light guide plate
100 much. That is, the light-emitting area B2 of the light guide
plate 100' has a relation of (extracted light quantity from the
side of the cold cathode fluorescent lamp 102a'/guided light
quantity from the side of the cold cathode fluorescent lamp
102a')>(extracted light quantity from the side of the cold
cathode fluorescent lamp 102b'/guided light quantity from the side
of the cold cathode fluorescent lamp 102b').
[0380] The light-emitting areas B2 and A2 of the light guide plate
100 are non-light-extraction areas in which both the light from the
side of the cold cathode fluorescent lamp 102a and the light from
the side of the cold cathode fluorescent lamp 102b are hardly
extracted. Besides, the light-emitting areas B1 and A1 of the light
guide plate 100' are non-light-extraction areas in which both the
light from the side of the cold cathode fluorescent lamp 102a' and
the light from the side of the cold cathode fluorescent lamp 102b'
are hardly extracted.
[0381] As stated above, in the light-emitting area A1 of the light
guide plate 100, the light guided from the side of the cold cathode
fluorescent lamp 102a is more extracted, and in the light-emitting
area B1, the light guided from the side of the cold cathode
fluorescent lamp 102b is more extracted. In the light-emitting area
A2 of the light guide plate 100', the light guided from the side of
the cold cathode fluorescent lamp 102a' is more extracted, and in
the light-emitting area B2, the light guided from the side of the
cold cathode fluorescent lamp 102b' is more extracted. Besides,
when the light guide plate 100 and 100' are laminated and disposed,
light is almost uniformly extracted in all the light-emitting areas
B1, A1, B2 and A2.
[0382] FIG. 68 shows a driving method of the illumination device
according to this example and the liquid crystal display device
using the same. The horizontal axis direction indicates time, and
the vertical axis direction indicates a writing state
(writing/non-writing) of gradation data and a blinking state
(ON/OFF) of the backlight unit 130. A waveform "a" indicates a
writing state of gradation data in the light-emitting area B1, and
a waveform "b" indicates a writing state of gradation data in the
area B2. A waveform "c" indicates a writing state of gradation data
in the area A1, and a waveform "d" indicates a writing state of
gradation data in the area A2. Besides, a waveform "e" indicates a
blinking state of the cold cathode fluorescent lamp 102b, and a
waveform "f" indicates a blinking state of the cold cathode
fluorescent lamp 102b'. A waveform "g" indicates a blinking state
of the cold cathode fluorescent lamp 102a, and a waveform "h"
indicates a blinking state of the cold cathode fluorescent lamp
102a'.
[0383] As shown in FIG. 68, a light source control part 132 (not
shown in FIG. 66) synchronizes with a latch pulse signal LP and
causes the cold cathode fluorescent lamps 102a, 102b, 102a' and
102b' to emit light for a specified time at a blinking frequency
equal to a frame frequency (for example, 60 Hz). Besides, the light
source control part 132 causes a timing at which the light emission
brightness of the cold cathode fluorescent lamp 102b is made
maximum to be different from a timing at which the light emission
brightness of the cold cathode fluorescent lamp 102b' is made
maximum by about 4.2 msec (1/4 period). Similarly, a timing at
which the light emission brightness of the cold cathode fluorescent
lamp 102b' is made maximum is different from a timing at which the
light emission brightness of the cold cathode fluorescent lamp 102a
is made maximum by about 4.2 msec, and a timing at which the light
emission brightness of the cold cathode fluorescent lamp 102a is
made maximum is different from a timing at which the light emission
brightness of the cold cathode fluorescent lamp 102a' is made
maximum by about 4.2 msec. Besides, a timing at which the light
emission brightness of the cold cathode fluorescent lamp 102a' is
made maximum is different from a timing at which the light emission
brightness of the cold cathode fluorescent lamp 102b is made
maximum by about 4.2 msec.
[0384] After a specified time has passed since gradation data was
written into pixels of the area B1, the cold cathode fluorescent
lamp 102b for causing the light-emitting area B1 to emit light is
turned on. Besides, after the cold cathode fluorescent lamp 102b is
turned off, gradation data is written into pixels of the area B1.
After a specified time has passed since gradation data was written
into pixels of the area B2, the cold cathode fluorescent lamp 102b'
for causing the light-emitting area B2 to emit light is turned on.
Besides, after the cold cathode fluorescent lamp 102b' is turned
off, gradation data is written into pixels of the area B2.
Similarly, a specified time has passed since gradation data was
written into pixels of the area A1, the cold cathode fluorescent
lamp 102a for causing the light-emitting area A1 to emit light is
turned on. Besides, after the cold cathode fluorescent lamp 102a is
turned off, gradation data is written into pixels of the area A1. A
specified time has passed since gradation data was written into
pixels of the area A2, the cold cathode fluorescent lamp 102a' for
causing the light-emitting area A2 to emit light is turned on.
Besides, after the cold cathode fluorescent lamp 102a' is turned
off, gradation data is written into pixels of the area A2.
[0385] As stated above, the cold cathode fluorescent lamp for
illuminating the area into which the gradation data is written is
turned off. In the liquid crystal display device, since it takes a
time of several msec to several tens msec until a liquid crystal
molecule is inclined at a specified inclination angle from the
writing of the gradation data into the pixel, when a time from the
writing of the gradation data of a certain area to the lighting of
the cold cathode fluorescent lamp for illuminating the area is
secured to the extent possible, more excellent display quality of a
motion picture can be obtained. Thus, in this example, immediately
after the cold cathode fluorescent lamp 102a is turned off, the
writing of the gradation data is started.
[0386] According to this example, the same effect as the example
5-1 can be obtained. Besides, in this embodiment, contrary to the
example 5-1, a multi-scan type liquid crystal display device is not
required, the scan-type illumination device and the liquid crystal
display device can be realized without complicating the driving
circuit. Incidentally, in this example, although the light guide
plate 100 and 100' include four divided light-emitting areas A1,
A2, B1 and B2, the number of divided areas is arbitrary.
[0387] According to this embodiment, it is possible to realize the
scan type illumination device and the liquid crystal display
device, which has the simple structure, is small, thin and light,
and has uniform brightness and color. Besides, according to this
embodiment, the liquid crystal display device without contour
blurring and excellent in the motion picture quality can be
realized.
Sixth Embodiment
[0388] An illumination device according to a sixth embodiment of
the invention and a liquid crystal display device using the same
will be described with reference to FIGS. 69 to 73. This embodiment
is characterized by a polarizing plate bonded to a liquid crystal
display device or an illumination device used for that, and is
characterized by a manufacturing method in a case where the
polarizing plate is bonded to a panel surface of the liquid crystal
display device or to a light guide plate of the illumination
device.
[0389] In general, a transmission liquid crystal display device is
constructed such that transmissivity of light incident from the
rear surface of a liquid crystal panel is modulated in a liquid
crystal layer and the light is emitted to the panel surface, and a
backlight unit as an illumination device is disposed at the rear
side of the liquid crystal panel. On the other hand, a reflection
liquid crystal display device for a mobile use is constructed such
that outside light is incident from the surface of a liquid crystal
panel, is made to pass through a liquid crystal layer and to be
reflected at a reflection electrode, is modulated in the liquid
crystal layer and is emitted to the panel surface.
[0390] In general, in the reflection liquid crystal display device,
as an auxiliary illumination light source at the time of less
outside light, a front light unit (for example, see the example 5-5
(FIG. 65) of the fifth embodiment) is disposed at the side of a
liquid crystal panel surface. The front light unit includes a
transparent plate-like light guide plate disposed at the side of
the liquid crystal panel surface, and a light source disposed at
least the side of one side surface of the light guide plate. A
prism is formed stepwise at the surface side (outside light
incident side) of the light guide plate at a small pitch of, for
example, 1 mm or less, and incident light from a light source at
the side of the light guide plate is reflected, refracted and
transmitted in the in-plane direction, and almost vertical light is
emitted to the whole surface of the liquid crystal panel surface.
Since the light guide plate is required to have high
transmissivity, to be easily molded, and to be light, the same
acryl material as the light guide plate for the backlight unit is
often used.
[0391] A polarizing plate is disposed between the light emission
surface of the light guide plate at the side of the liquid crystal
panel surface and the liquid crystal panel surface. When this
polarizing plate is bonded to the light emission surface of the
light guide plate at the side of the liquid crystal panel surface,
it is possible to absorb unnecessary light incident on the liquid
crystal panel surface from the light guide plate at a relatively
large incident angle, to suppress the degradation (black floating
or the like) of picture quality, and to obtain a high contrast
display.
[0392] Since the front light unit is mainly used for a small liquid
crystal display device, the light guide plate is required to be
light and small. Thus, the light guide plate is formed of a very
thin plate having a thickness of about 1 mm and has such a
structure that it is easily deformed. On the other hand, in the
polarizing plate bonded to the light guide plate, a heat shrinkage
of 0.3% to 0.5% occurs under a high temperature. Thus, there arises
a problem that when the polarizing plate is heat shrunk under a
high temperature, the light guide plate is deformed. For example,
in the case where a liquid crystal display device is left in, for
example, an automobile on a summer day and is put under a high
temperature on the day, the polarizing plate is shrunk and bends
the light guide plate, and even if it is again put in the place of
room temperature, the shrinkage is kept as it is, and therefore,
the deformation of the light guide plate remains. Although a
protection cover to prevent the surface prism of the light guide
plate from being soiled is provided at the outside light incident
side of the light guide plate of the front light unit, when the
light guide plate is bent and comes in contact with this protection
cover, both are rubbed and the light guide plate is scratched, and
a bad influence is given on the display quality to cause uneven
brightness or the like. In order to avoid this, when a distance
between the light guide plate and the protection cover is
previously made long, a gap of about 5 mm is required, which
increases the thickness of the device. Besides, when the light
guide plate itself is deformed, the center of the light guide plate
expands to become a crest, circular moire fringes are produced and
the display quality is degraded.
[0393] In order to solve this problem, in this embodiment, it has
been found that the heat shrinkage of the polarizing plate is
irreversible, and the heat shrinkage is saturated at 0.3 to 0.5%,
and therefore, the polarizing plate is previously subjected to heat
treatment to cause irreversible shrinkage and then used. The heat
treatment is performed in such a way that the polarizing plate is
left in a specified temperature environment for a specific time. At
this time, when the heat treatment temperature is made 100.degree.
C. or higher, the degradation of the polarizing plate itself occurs
so that the degree of polarization is rapidly lowered and the
contrast of a display is lowered, and accordingly, attention must
be paid. Besides, when the heat treatment temperature becomes
40.degree. C. or less, since the progress of the heat shrinkage of
the polarizing plate becomes slow, it takes a long time to perform
the heat treatment, and attention must be paid in an actual
manufacture process.
[0394] When the polarizing plate is subjected to a suitable heat
treatment while attention is given to such a range of the heat
treatment temperature, even in the case where the liquid crystal
display device is left under a high temperature, the deformation
quantity of the light guide plate can be made small, and
accordingly, the distance between the light guide plate and the
protection cover is made small, and the device volume can be made
small. Besides, since the deformation of the light guide plate can
be made small, the degradation of the display quality due to the
moire fringes can also be made slight. Further, when the
environment temperature is returned to room temperature, the
deformation of the light guide plate is returned to the original,
so that the display quality is also not damaged.
[0395] Hereinafter, a description will be given of specific
examples. FIG. 69 shows a manufacturing method of an illumination
device according to this embodiment. As shown in FIG. 69, first, at
a polarizing plate heat treatment step 91, a polarizing plate is
subjected to heat treatment in a constant temperature bath at a
specified temperature. Thereafter, the temperature is returned to
the room temperature, and then a bonding step 92 to the light guide
plate is started, and the polarizing plate is bonded to the surface
of the light guide plate by a bonding machine. Next, an autoclave
treatment is performed (autoclave treatment step 93). Next, at an
attachment step 94 of a lamp assembly, a light source and the like
are attached to the light guide plate, and a front light is
completed.
[0396] Next, conditions and the like for suitably carrying out the
polarizing plate heat treatment step 91 will be described in
detail. First, an examination is carried out on a change of
wavelength (hereinafter referred to as a cut wavelength shift
amount) at which transmissivity of the polarizing plate in an
absorption axis becomes 50% and a change of shrinkage percentage
according to a heat treatment temperature and a heat treatment time
(see FIG. 70). It is known that the use upper temperature of a
polarizing plate recommended by a manufacture maker is usually
about 70.degree. C., and when it is exposed to a temperature higher
than that, the deterioration of the polarizing plate is
accelerated. The deterioration of the polarizing plate is the
deterioration of the degree of polarization, and the degree of
deterioration is found by measuring the cut wavelength in the
absorption axis and examining the shift (see FIG. 71).
[0397] FIG. 70 shows the cut wavelength change in the polarizing
plate absorption axis with respect to the heat treatment time in
the heat treatment of the polarizing plate in the illumination
device according to this embodiment. The horizontal axis indicates
the heat treatment time (hr), and the vertical axis indicates the
cut wavelength shift amount (nm). In the drawing, a broken line
having a short pitch indicates data obtained when the heat
treatment temperature to the polarizing plate is 50.degree. C.
Similarly, an alternate long and short dash line indicates data
obtained when the heat treatment temperature is 60.degree. C., a
thin solid line indicates data obtained when the heat treatment
temperature is 70.degree. C., and a broken line having a long pitch
indicates data obtained when the heat treatment temperature is
100.degree. C. Besides, a thick solid line indicates the cut
wavelength shift amount of a polarizing plate used for a 17-inch
liquid crystal display device, which is comparative data obtained
for a case where the polarizing plate not subjected to heat
treatment is bonded to a light guide plate, and is denoted by "in
17-inch device" in the drawing.
[0398] As shown in FIG. 70, the cut wavelength shift amount of "in
17-inch device" indicated by the thick solid line is -6 nm at the
heat treatment of 500 hr, and -11 nm at the heat treatment of 1000
hr. As compared with this, in the polarizing plate subjected to
heat treatment at a temperature of 50.degree. C. or higher, as the
heat treatment temperature becomes high, the cut wavelength shift
amount in the same heat treatment time is increased, and the
deterioration is accelerated. Here, it is understood that when the
heat treatment temperature is 70.degree. C. or lower, and the heat
treatment time does not exceed 50 hr, the cut wavelength shift
amount is -11 nm or less, and is equivalent to the degradation of
1000 hr in the comparative data of "in 17-inch device". The time of
1000 hr is 3% of the lifetime of the 17-inch liquid crystal display
device, and is put in an allowable range in terms of the quantity
of deterioration at the polarizing plate heat treatment.
[0399] FIG. 71 shows a transmission characteristic of the
polarizing plate in an absorption axis direction in a case where
the polarizing plate is subjected to heat treatment at 70.degree.
C. The horizontal axis indicates a wavelength (mm), and the
vertical axis indicates a transmissivity (%). In the drawing, a
solid line indicates a transmission characteristic in a case where
the heat treatment time is 2000 hours, and a broken line indicates
a transmission characteristic in a case where the heat treatment
time is 0 hour (that is, heat treatment is not performed). As
compared with the case where the heat treatment is not performed,
the cut wavelength of the polarizing plate in the absorption axis
is lowered from about 810 nm to about 785 nm.
[0400] FIG. 72 shows a change of shrinkage percentage of the
polarizing plate with respect to a heat treatment time in the
illumination device according to this embodiment. The horizontal
axis indicates a heat treatment time (hr), and the vertical axis
indicates a shrinkage percentage. A solid line in the drawing
indicates a case where the heat treatment temperature is 70.degree.
C., and a broken line indicates a case where the heat treatment
temperature is 60.degree. C. With respect to the shrinkage
percentage of the polarizing plate, the lengths of the horizontal
and vertical sides of the polarizing plate are measured before and
after the heat treatment, and an average of the changes with
respect to the original length is calculated. As the heat treatment
temperature becomes high, the shrinkage of the polarizing plate is
accelerated, and therefore, in this example, the changes at the
heat treatment temperatures of 60.degree. C. and 70.degree. C. are
indicated. Although the heat shrinkage percentages of both become
identical in the case where the heat treatment time is 100 hr or
more, the rate of the heat shrinkage is faster when the heat
treatment temperature is 70.degree. C., and the shrinkage of the
polarizing plate becomes almost saturated by the treatment of 40 to
50 hr. Also with respect to the cut wavelength shift amount in the
polarizing plate absorption axis shown in FIG. 70, since it is
apparent as described above that the heat treatment time of 50 hr
or less is preferable, it is understood that the heat treatment is
suitable when the heat treatment temperature is 70.degree. C.
Besides, from FIG. 72, when the heat treatment temperature is made
70.degree. C., the heat treatment time of 40 hr in which the heat
shrinkage is almost saturated is desirable.
[0401] Then, the polarizing plate subjected to the heat treatment
at the heat treatment temperature of 70.degree. C. and the heat
treatment time of 40 hr is bonded to the light guide plate, and the
deformation quantity of the light guide plate is measured using a
thermal shock test machine. Specifically, four sides of a front
light unit in which light sources are attached to ends of the light
guide plate to which the polarizing plate is bonded, are fixed onto
the liquid crystal panel and a thermal shock test of a temperature
of 60.degree. C. for 25 minutes and a temperature of -20.degree. C.
for 35 minutes is performed. With respect to the deformation
quantity of the light guide plate, a distance between a most raised
portion of the center of the light guide plate and an edge of the
light guide plate is measured and is made the deformation
quantity.
[0402] FIG. 73 shows a relation between a thermal shock test time
and a light guide plate deformation quantity in the illumination
device according to this embodiment. The horizontal axis indicates
a thermal shock test time (hr) and the vertical axis indicates a
deformation quantity (mm) of a light guide plate. In the drawing, a
solid line indicates a polarizing plate subjected to heat
treatment, and a broken line indicates a polarizing plate not
subjected to heat treatment.
[0403] In the conventional polarizing plate (broken line) which is
not subjected to the heat treatment, the deformation quantity is
4.6 mm when the thermal shock test time is 600 hr, and on the other
hand, in the polarizing plate (solid line) subjected to the heat
treatment, the deformation quantity is 1.0 mm when the shock test
time is 600 hr, and the deformation can be suppressed to 39% of the
related art.
[0404] As described above, according to this embodiment, the
polarizing plate is subjected to a suitable heat treatment to cause
irreversible heat shrinkage in advance and then, it is bonded to a
light guide plate, and a front light unit is manufactured.
Especially, it is preferable that a heat shrinkage quantity .alpha.
is in a range of 0<.alpha..ltoreq.0.3%. By doing so, even in the
case where the liquid crystal display device is left under a high
temperature, the deformation quantity of the light guide plate can
be greatly suppressed. Accordingly, the distance between the light
guide plate and the protection cover can be shortened by 1 to 2 mm,
and the device volume can be made small. Besides, since the
deformation quantity of the light guide plate is small, the moire
fringes become slight, and when the environmental temperature is
returned to the room temperature, the deformation is removed and
the shape returns to an original one, and therefore, the display
quality is also not damaged.
[0405] Incidentally, in this embodiment, although the description
has been given of the case, as an example, where the polarizing
plate is bonded to the light emission surface of the light guide
plate of the front light unit at the side of the liquid crystal
panel surface, in addition to this case, a desired effect can be
obtained also when this embodiment is applied to a case where the
light guide plate is bonded to the light guide plate at the side of
the outside light incident surface, a case where it is bonded to
the liquid crystal panel surface, or a case where it is bonded to
the light guide plate of the backlight unit.
[0406] Besides, the structure of the polarizing plate will be
specifically described. As the polarizing plate, there is, for
example, a polarizing film single body in which polyvinyl alcohol
(PVA) is drawn and is colored with iodine, a polarizing plate
having such a structure that for example, triacetyl cellulose (TAC)
films as protection films are bonded to both sides of the
polarizing film, or a polarizing plate in which retardation films
having different linear expansion coefficients are laminated. This
embodiment can be applied to all of the above polarizing
plates.
[0407] The invention is not limited to the above embodiment, but
can be variously modified.
[0408] For example, in the above embodiment, although the active
matrix type liquid crystal display device is exemplified, the
invention is not limited to this, but can also be applied to a
simple matrix liquid crystal display device.
[0409] Besides, in the above embodiment, although the description
has been given of the case where the light-emitting area is divided
into four areas, the invention is not limited to this, and the area
can be divided into an arbitrary number of areas.
[0410] Further, in the above embodiment, although the TN mode
liquid crystal display device is exemplified, the invention is not
limited to this, but can be applied to another liquid crystal
display device such as an MVA mode one or an IPS mode one.
Seventh Embodiment
[0411] A liquid crystal display device according to a seventh
embodiment of the invention will be described with reference to
FIGS. 77 to 85. This embodiment relates to the liquid crystal
display device including a vertical aligned liquid crystal display
area.
[0412] FIG. 84 is a schematic structural view showing a main part
of an example of a conventional liquid crystal display device (for
example, see patent document 8). In FIG. 84, reference numeral 201
denotes an active matrix type color liquid crystal display panel in
which thin film transistors (TFTs) are used as switching elements
and which operates in a vertical alignment mode; 202, a backlight
as a light source of the color liquid crystal display panel; and
203, an inverter as a power source of the backlight 202.
[0413] Reference numeral 204 denotes a data driver (data line
driving circuit) for outputting RGB signals to data lines formed in
the color liquid crystal display panel 201; and 205, a gate driver
(gate line driving circuit) for outputting gate signals (scanning
signals) to gate lines formed in the color liquid crystal display
panel 201.
[0414] Reference numeral 206 denotes a timing controller which
receives a dot clock DCLK given from a display signal source (for
example, a computer), a vertical synchronization signal Vsync, a
display signal synchronization signal (display signal effective
area specified signal) ENAB and RGB data signals R0 to R6, G0 to
G6, and B0 to B6, and supplies various signals necessary for
driving the color liquid crystal display panel 201 to the data
driver 204 and the gate driver 205.
[0415] FIG. 85 is a timing chart showing the operation of the
conventional liquid crystal display device shown in FIG. 84, and
shows the dot clock DCLK inputted to the timing controller 206, the
vertical synchronization signal Vsync inputted to the timing
controller 206, the display signal synchronization signal ENAB
inputted to the timing controller 206, the RGB data signal inputted
to the timing controller 206, and the RGB data signal given from
the timing controller 206 to the data driver 204.
[0416] In the conventional liquid crystal display device shown in
FIG. 84, the RGB data signals R0 to R6, G0 to G6 and B0 to B6 given
from the display signal source are captured in the timing
controller 206 in synchronization with the display signal
synchronization signal ENAB, are subjected to timing adjustment and
are supplied to the data driver 204.
[0417] In the conventional liquid crystal display device shown in
FIG. 84, the vertical aligned liquid crystal display panel
operating in the vertical alignment mode is provided as the color
liquid crystal display panel 201, and the vertical aligned liquid
crystal display panel has a problem that when a picture plane is
changed, in the case where an "edge" exists in the gradation
displayed on a former picture plane (for example, in the case where
the background is black and a gray object having an "edge" is
displayed), and a next screen is a white display, a holding type
afterimage is apt to occur.
[0418] The holding type afterimage occurs in such a way that in a
portion where a picture plane is changed from an intermediate
gradation (for example, gray) to white, when the picture plane is
changed, a state in which the alignment of a liquid crystal is
disturbed is held as it is, and a difference is seen against a
portion where black having a uniform alignment is changed to
white.
[0419] In view of the above pint, this embodiment has an object to
provide a liquid crystal display device in which even in the case
where a vertical aligned liquid crystal display area is included, a
holding type afterimage is made not to occur easily, and a high
quality image display can be carried out.
[0420] This embodiment is a liquid crystal display device including
a vertical aligned liquid crystal display area, and includes a
black display control part which can cause a specified area of a
screen to produce a black display at a time of driving of the
liquid crystal display area.
[0421] According to this embodiment, at the time of the driving of
the liquid crystal display area, since the picture plane can be
made to produce the black display by the black display control
part, the alignment of the liquid crystal can be made uniform.
Accordingly, the holding type afterimage can be made not to occur
easily.
[0422] Hereinafter, examples 7-1 to 7-3 of this embodiment will be
described with reference to FIGS. 77 to 83. Incidentally, in FIGS.
77, 80 and 82, portions corresponding to those of FIG. 84 are
denoted by the same symbols and the duplicate description will be
omitted.
Example 7-1
[0423] FIG. 77 is a schematic structural view showing a main part
of example 7-1. The example 7-1 includes an inverter 207 and a
timing controller 208 which are different in structure from the
inverter 203 and the timing controller 206 included in the
conventional liquid crystal display device shown in FIG. 84, and
the other structure is the same as the conventional liquid crystal
display device shown in FIG. 84.
[0424] The inverter 207 includes a lighting control terminal 209,
and in a period in which the lighting control terminal 209 is made
to have an L level, a lighting state of a backlight 202 is kept,
and in a period in which the lighting control terminal 209 is made
to have an H level, the backlight 202 is put in a non-lighting
state. A lighting control signal SA is given to the lighting
control terminal 209 from the timing controller 208.
[0425] The timing controller 208 includes a black display control
part 210, supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6
outputted from the black display control part 210 to a data driver
204, and outputs a black display control signal generated by the
black display control part 210 as the lighting control signal SA,
and the other part of the timing controller is the same as the
conventionally known structure.
[0426] FIG. 78 is a circuit diagram showing the structure of the
black display control part 210. In FIG. 78, reference numeral 211
denotes a black display control signal generation circuit for
generating a black display control signal SB; and 212, a frame end
part detection circuit which receives a display signal
synchronization signal ENAB (or a vertical synchronization signal
Vsync) and a dot clock DCLK, detects an end part of a frame, and
outputs one frame end part detection pulse SC for one frame.
[0427] Reference numeral 213 denotes an N-pulse counter (N is, for
example, 60) for counting the frame end part detection pulse SC
outputted from the frame end part detection part 212; and 214, a
decoder for decoding the output of the N-pulse counter 213 and
outputting, once every N frames, a black display control signal SB
to cause one frame period to have the H level.
[0428] Reference numeral 215 denotes a three-system two-input
one-output selector for selecting the RGB data signals R0 to R6, G0
to G6 and B0 to B6, or the black display data signal and supplying
it to the data driver 204; SL, a select control signal input
terminal; A1 to A3 and B1 to B3, selected signal input terminals;
and X1 to X3, output terminals.
[0429] The black display control signal SB is given to the select
control signal input terminal SL, the R data signals R0 to R6 are
given to the selected signal input terminal A1, the G data signals
G0 to G6 are given to the selected signal input terminal A2, the B
data signals B0 to B6 are given to the selected signal input
terminal A3, and the ground potential of 0 V is given to the
selected signal input terminals B1 to B3.
[0430] In the case of the black display control signal SB=L level,
the selector 215 selects the RGB data signals R0 to R6, G0 to G6
and B0 to B6 given to the selected signal input terminals A1 to A3
and supplies them to the data driver 204, and in the case of the
black display control signal SC=H level, the selector supplies the
ground potential of 0 V given to the selected signal input
terminals B1 to B3 as the black data signal to the data driver
204.
[0431] FIG. 79 is a timing chart showing the operation of the
example 7-1, and shows the dot clock DCLK inputted to the timing
controller 208, the vertical synchronization signal Vsync inputted
to the timing controller 208, the display synchronization signal
ENAB inputted to the timing controller 208, the RGB data signal
inputted to the timing controller 208, and the RGB data signal
given from the timing controller 208 to the data driver 204.
[0432] That is, in the example 7-1, since the black display control
signal generation circuit 211 outputs, once every N frames (for
example, 60 frames), the black display control signal SB to cause
one frame period to have the H level, the selector 215 supplies the
RGB data signals R0 to R6, G0 to G6 and B0 to B6 to the data driver
204 in the (N-1) frame periods of the N frame periods, and supplies
the black display data signal in one frame period of the N frame
periods so that a black picture plane is displayed on the color
liquid crystal display panel 201.
[0433] Besides, the black display control signal SB outputted from
the black display control signal generation circuit 211 is supplied
as the lighting control signal SA to the lighting control terminal
209 of the inverter 207. Accordingly, in the case where the black
picture plane is displayed on the color liquid crystal display
panel 201 by the control of the black display control part 210, the
backlight 202 is put in the non-lighting state.
[0434] As stated above, according to the example 7-1, since the
black picture plane is displayed on the color liquid crystal
display panel 201 in the one frame period of the N frame periods,
even if the vertical alignment mode color liquid crystal display
panel 201 is provided, the alignment of the liquid crystal of the
whole screen can be made uniform, and the holding type afterimage
can be cancelled, so that the high quality image display can be
carried out.
[0435] Besides, in the case where the black picture plane is
displayed on the color liquid crystal display panel 201 by the
control of the black display control part 210, since the backlight
202 is put in the non-lighting state, it is possible to avoid
perceptually recognizing the black display picture plane.
Incidentally, also in the case where the black picture plane is
displayed on the color liquid crystal display panel 201 by the
control of the black display control part 210, the backlight 202
may keep the lighting state.
Example 7-2
[0436] FIG. 80 is a schematic structural view showing a main part
of example 7-2. The example 7-2 includes an inverter 216 and a
timing controller 217 which are different in structure from the
inverter 203 and the timing controller 206 included in the
conventional liquid crystal display device shown in FIG. 84, and
the other structure is the same as the conventional liquid crystal
display device shown in FIG. 84.
[0437] When the number of horizontal lines of a color liquid
crystal display panel 201 is 4m (m is, for example, 192), a
backlight 202 includes a first fluorescent lamp corresponding to
the first to m-th horizontal lines, a second fluorescent lamp
corresponding to the (m+1)-th to 2m-th horizontal lines, a third
fluorescent lamp corresponding to the (2m+1)-th to 3m-th horizontal
lines, and a fourth fluorescent lamp corresponding to the (3m+1)-th
to 4m-th horizontal lines. The inverter 216 includes lighting
control terminals 218-1 to 218-4 corresponding to the first to the
fourth fluorescent lamps.
[0438] Then, the inverter 216 keeps the lighting state of the i-th
fluorescent lamp in the period when the lighting control terminal
218-i (i=1, 2, 3, 4) is made to have the L level, and the inverter
brings the i-th fluorescent lamp into the non-lighting state in the
period when the lighting control terminal 218-i is made to have the
H level. Alighting control signal SAi is given to the lighting
control terminal 218-i from the timing controller 217.
[0439] The timing controller 217 includes a black display control
part 219, supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6
outputted from the black display control part 219 to a data driver
204, and generates lighting control signals SA1 to SA4 by the black
display control part 219, and the other part of the timing
controller is the same as the conventionally known structure.
[0440] FIG. 81 is a circuit diagram showing the structure of the
black display control circuit 219. In FIG. 81, reference numeral
220 denotes a black display control signal generation circuit which
receives a display signal synchronization signal ENAB (or a
vertical synchronization signal Vsync) and a dot clock DCLK, and
generates a first black display control signal SB, and has the same
circuit structure as the black display control signal generation
circuit 211 shown in FIG. 78.
[0441] Reference numeral 221 denotes a black display control signal
generation circuit for generating a second black display control
signal SD; 222, a horizontal line number detection circuit which
receives a display signal synchronization signal ENAB (or a clock
GCLK for a gate driver 205), detects the number of horizontal
lines, and outputs one pulse SE each time m horizontal lines are
detected; and 223, a 4-pulse counter for counting the pulse SE
outputted from the horizontal line number detection circuit
222.
[0442] Reference numeral 224-1 denotes a decoder which decodes the
output of the 4-pulse counter 223, outputs the L level in a period
when the count value of the 4-pulse counter 223 is 2, and outputs
the H level in the other period. Reference numeral 224-2 denotes a
decoder which decodes the output of the 4-pulse counter 223,
outputs the L level when the count value of the 4-pulse counter 223
is 3, and outputs the H level in the other period.
[0443] Reference numeral 224-3 denotes a decoder which decodes the
output of the 4-pulse counter 223, outputs the L level in a period
when the count value of the 4-pulse counter 223 is 4, and outputs
the H level in the other period. Reference numeral 224-4 denotes a
decoder which decodes the output of the 4-pulse counter 223,
outputs the L level in a period when the count value of the 4-pulse
counter 223 is 1, and outputs the H level in the other period.
[0444] Reference numerals 225-1 to 225-4 denote JK flip-flops. In
the JK flip-flop 225-1, the pulse SE outputted from the horizontal
line number detection circuit 222 is given to a J terminal, and the
output of the decoder 224-1 is given to a K terminal. In the JK
flip-flop 225-2, the output of the decoder 224-1 is given to a J
terminal, and the output of the decoder 224-2 is given to a K
terminal.
[0445] In the JK flip-flop 225-3, the output of the decoder 224-2
is given to a J terminal, and the output of the decoder 224-3 is
given to a K terminal. In the JK flip-flop 225-4, the output of the
decoder 224-3 is given to a J terminal, and the output of the
decoder 224-4 is given to a K terminal.
[0446] Reference numeral 226 denotes a 4-input 1-output selector; A
to D, selected signal input terminals; and SL1 and SL2, select
control signal input terminals. The selector 226 selects the
selected signal input terminal A at the time of SL1=L level and
SL2=L level, selects the selected signal input terminal B at the
time of SL1=L level and SL2=H level, selects the selected signal
input terminal C at the time of SL1=H level and SL2=L level, and
selects the selected signal input terminal D at the time of SL1=H
level and SL2=H level.
[0447] The output of the JK flip-flop 225-1 is given to the
selected signal input terminal A, the output of the JK flip-flop
225-2 is given to the selected signal input terminal B, the output
of the JK flip-flop 225-3 is given to the selected signal input
terminal C, and the output of the JK flip-flop 225-4 is given to
the selected signal input terminal D.
[0448] Reference numeral 227 denotes a black display area selection
circuit, which outputs black display area selection signals SF1 and
SF2 and lighting control signals SA1 to SA4, gives the black
display area selection signals SF1 and SF2 to the select control
signal input terminals SL1 and SL2 of the selector 226, and gives
the lighting control signals SA1 to SA4 to the lighting control
terminals 218-1 to 218-4 of the inverter 216.
[0449] The black display area selection circuit 227 takes a state
of SF1=L level and SF2=L level, a state of SF1=L level and SF2=H
level, a state of SF1=H level and SF2=L level, and a state of SF1=H
level and SF2=H level in sequence one by one every N frames, and as
a result, the selector 226 selects and outputs the outputs of the
JK flip-flops 225-1 to 225-4 in sequence one by one every N
frame.
[0450] Reference numeral 228 denotes an AND circuit for performing
an AND operation of the black display control signal SB outputted
from the black display control signal generation circuit 220 and
the black display control signal SD outputted from the black
display control signal generation circuit 221; 229, a 3-system
2-input 1-output selector; SL, a select control signal input
terminal; A1 to A3 and B1 to B3, selected signal input terminals;
and X1 to X3, output terminals.
[0451] The output of the AND circuit 228 is given to the select
control signal input terminal SL, the R data signals R0 to R6 are
given to the selected signal input terminal A1, the G data signals
G0 to G6 are given to the selected signal input terminal A2, the B
data signals B0 to B6 are given to the selected signal input
terminal A3, and the ground potential of 0 V is given to the
selected signal input terminals B1 to B3.
[0452] In the case where the output of the AND circuit 228 is the L
level, the selector 229 selects the RGB data signals R0 to R6, G0
to G6, B0 to B6 given to the selected signal input terminals A1 to
A3 and supplies them to the data driver 204, and in the case where
the output of the AND circuit 228 is the H level, the selector
supplies the ground potential of 0 V given to the selected signal
input terminals B1 to B3 as the black display data signal to the
data driver 204.
[0453] In the example 7-2, the black display control signal
generation circuit 220 outputs, once every N frames (for example,
60 frames), the black display control signal SB to cause one frame
period to have the H level, and the black display control signal
generation circuit 221 selects and outputs the outputs of the JK
flip-flops 225-1 to 225-4 in sequence one by one every N
frames.
[0454] As a result, the AND circuit 228 outputs the H level in the
scanning period of the first to the m-th horizontal lines of the
(N+1)-th frame, outputs the H level in the scanning period of the
(m+1)-th to the 2m-th horizontal lines of the (2N+1)-th frame,
outputs the H level in the scanning period of the (2m+1)-th to the
3m-th horizontal lines of the (3N+1)-th frame, and outputs the H
level in the scanning period of the (3m+1)-th to the 4m-th
horizontal lines of the (4N+1)-th frame, and subsequently, this
operation is repeated.
[0455] That is, the area of the first to the m-th horizontal lines,
the area of the (m+1)-th to the 2m-th horizontal lines, the area of
the (2m+1)-th to the 3m-th horizontal lines, and the area of the
(3m+1)-th to the 4m-th horizontal lines are black displayed in
sequence one by one every N frames.
[0456] Then, in this example, the black display area selection
circuit 227 is constructed to output the lighting control signals
SA1 to SA4 so that the first fluorescent lamp is turned off when
the area of the first to the m-th horizontal lines is black
displayed, the second fluorescent lamp is turned off when the area
of the (m+1)-th to the 2m-th horizontal lines is black displayed,
the third fluorescent lamp is turned off when the area of the
(2m+1)-th to the 3m-th horizontal lines is black displayed, and the
fourth fluorescent lamp is turned off when the area of the
(3m+1)-th to the 4m-th horizontal lines is black displayed.
[0457] As stated above, according to the example 7-2, since the
black picture plane can be displayed in the four divided screen
areas in the vertical direction in sequence one by one every N
frames, even if the vertical alignment mode color liquid crystal
display panel 201 is included, the alignment of the liquid crystal
of the whole screen can be made uniform, and the holding type
afterimage can be cancelled. Accordingly, the high quality image
display can be carried out.
[0458] Besides, since the fluorescent tubes provided
correspondingly to the black-displayed picture plane areas can be
turned off by the lighting control signals SA1 to SA4 outputted by
the black display area selection circuit 227, it is possible to
avoid perceptually recognizing the black display picture plane.
Incidentally, also in the case where the black picture plane is
displayed on the color liquid crystal display panel 201 by the
control of the black display control part 219, the backlight 202
may keep the lighting state.
Example 7-3
[0459] FIG. 82 is a schematic structural view showing a main part
of example 7-3. The example 7-3 includes a backlight 202A, an
inverter 230 and a timing controller 231 which are different in
structure from the backlight 202, the inverter 203 and the timing
controller 206 included in the conventional liquid crystal display
device shown in FIG. 84, and the other structure is the same as the
conventional liquid crystal display device shown in FIG. 84.
[0460] When the number of vertical lines of a color liquid crystal
display panel 201 is 4n (n is, for example, 256), the backlight
202A includes a first fluorescent lamp corresponding to the first
to the n-th vertical lines, a second fluorescent lamp corresponding
to the (n+1)-th to the 2n-th vertical lines, a third fluorescent
lamp corresponding to the (2n+1)-th to the 3n-th vertical lines,
and a fourth fluorescent lamp corresponding to the (3n+1)-th to the
4n-th vertical lines. The inventor 230 includes lighting control
terminals 232-1 to 232-4 correspondingly to the first to the fourth
fluorescent lamps.
[0461] Then, the inventor 230 keeps the lighting state of the i-th
fluorescent lamp in a period when the lighting control terminal
232-i (i=1, 2, 3, 4) is made to have the L level, and brings the
ith fluorescent lamp into the non-lighting state in a period when
the lighting control terminal 232-i is made to have the H level. A
lighting control signal SGi is given to the lighting control
terminal 232-i from the timing controller 231.
[0462] The timing controller 231 includes a black display control
part 233, supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6
outputted from the black display control part 233 to a data driver
204, and generates lighting control signals SG1 to SG4 by the black
display control part 233, and the other part of the timing
controller is the same as the conventionally known structure.
[0463] FIG. 83 is a circuit diagram showing the structure of the
black display control part 233. In FIG. 83, reference numeral 234
denotes a black display control signal generation circuit which
receives a display signal synchronization signal ENAB (or a
vertical synchronization signal Vsync) and a dot clock DCLK and
generates a first black display control signal SB, and has the same
circuit structure as the black display control signal generation
circuit 211 shown in FIG. 78.
[0464] Reference numeral 235 denotes a black display control signal
generation circuit for generating a second black display control
signal SH; 236, a dot number detection circuit which receives a
display signal synchronization signal ENAB (or a gate clock GCLK)
and a dot clock DCLK, detects the number of dots, and outputs one
pulse S1 each time n dots are detected; and 237, a 4-pulse counter
for counting the pulse S1 outputted from the dot number detection
circuit 236.
[0465] Reference numeral 238-1 denotes a decoder which decodes the
output of the 4-pulse counter 237, outputs the L level in a period
when the count value of the 4-pulse counter 237 is 2, and outputs
the H level in the other period. Reference numeral 238-2 denotes a
decoder which decodes the output of the 4-pulse counter 237,
outputs the L level in a period when the count value of the 4-pulse
counter 237 is 3, and outputs the H level in the other period.
[0466] Reference numeral 238-3 denotes a decoder which decodes the
output of the 4-pulse counter 237, outputs the L level in a period
when the count value of the 4-pulse counter 237 is 4, and outputs
the H level in the other period. Reference numeral 238-4 denotes a
decoder which decodes the output of the 4-pulse counter 237,
outputs the L level in a period when the count value of the 4-pulse
counter 237 is 1, and outputs the H level in the other period.
[0467] Reference numerals 239-1 to 239-4 denote JK flip-flops. In
the JK flip-flop 239-1, the pulse S1 outputted from the dot number
detection circuit 236 is given to a J terminal, and the output of
the decoder 238-1 is given to a K terminal. In the JK flip-flop
239-2, the output of the decoder 238-1 is given to a J terminal,
and the output of the decoder 238-2 is given to a K terminal.
[0468] In the JK flip-flop 239-3, the output of the decoder 239-2
is given to a J terminal, and the output of the decoder 238-3 is
given to a K terminal. In the JK flip-flop 239-4, the output of the
decoder 238-3 is given to a J terminal, and the output of the
decoder 238-4 is given to a K terminal.
[0469] Reference numeral 240 denotes a 4-input 1-output selector; A
to D, selected signal input terminals; and SL1 and SL2, select
control signal input terminals. The selector 240 selects the
selected signal input terminal A at the time of SL1=L level and
SL2=L level, selects the selected signal input terminal B at the
time of SL1=L level and SL2=H level, selects the selected signal
input terminal C at the time of SL1=H level and SL2=L level, and
selects the selected signal input terminal D at the time of SL1=H
level and SL2=H level.
[0470] The output of the JK flip-flop 239-1 is given to the
selected signal input terminal A, the output of the JK flip-flop
239-2 is given to the selected signal input terminal B, the output
of the JK flip-flop 239-3 is given to the selected signal input
terminal C, and the output of the JK flip-flop 239-4 is given to
the selected signal input terminal D.
[0471] Reference numeral 241 denotes a black display area selection
circuit, outputs black display area selection signals SJ1 and SJ2
and lighting control signals SG1 to SG4, supplies the black display
area selection signals SJ1 and SJ2 to the select control signal
input terminals SL1 and SL2 of the selector 240, and supplies the
lighting control signals SG1 to SG4 to the lighting control
terminals 232-1 to 232-4 of the inverter 230.
[0472] The black display area selection circuit 241 takes a state
of SJ1=L level and SJ2=L level, a state of SJ1=L level and SJ2=H
level, a state of SJ1=H level and SJ2=L level, and a state of SJ1=H
level and SJ2=H level in sequence one by one every horizontal
scanning, and as a result, the selector 240 selects and outputs the
outputs of the JK flip-flop 239-1 to 239-4 in sequence one by one
every horizontal scanning.
[0473] Reference numeral 242 denotes an AND circuit for performing
an AND operation of the black display control signal SB outputted
from the black display control signal generation circuit 234 and
the black display control signal SH outputted from the black
display control signal generation circuit 235; 243, a 3-system
2-input 1-output selector; SL, a select control signal input
terminal; A1 to A3 and B1 to B3, selected signal input terminals;
and X1 to X3, output terminals.
[0474] The output of the AND circuit 242 is given to the select
control signal input terminal SL, the R data signals R0 to R6 are
given to the selected signal input terminal A1, the G data signals
G0 to G6 are given to the selected signal input terminal A2, the B
data signals B0 to B6 are given to the selected signal input
terminal A3, and the ground potential of 0 V is given to the
selected signal input terminals B1 to B3.
[0475] The selector 243 selects and outputs the RGB data signals R0
to R6, G0 to G6 and B0 to B6, which are given to the selected
signal input terminals A1 to A3, to the data driver 204 in the case
where the output of the AND circuit 242 is the L level, and
supplies the ground potential of 0 V, which is given to the
selected signal input terminals B1 to B3, as the black display data
signal to the data driver 204 in the case where the output of the
AND circuit 242 is the H level.
[0476] In the example 7-3, the black display control signal
generation circuit 234 outputs, once every N frames (for example,
60 frames), the black display control signal SB to cause one frame
period to have the H level, and the black display control signal
generation circuit 235 selects and outputs the outputs of the JK
flip-flops 239-1 to 239-4 in sequence one by one every horizontal
scanning.
[0477] As a result, the AND circuit 242 outputs the H level in the
scanning period of the first to the n-th vertical lines of the
(N+1)-th frame, outputs the H level in the scanning period of the
(n+1)-th to the 2n-th vertical lines of the (2N+1) frame, outputs
the H level in the scanning period of the (2n+1)-th to the 3n-th
vertical lines of the (3N+1)-th frame, and outputs the H level in
the scanning period of the (3n+1)-th to the 4n-th vertical lines of
the (4N+1)-th frame, and subsequently, this operation is
repeated.
[0478] That is, the area of the first to the n-th vertical lines,
the area of the (n+1)-th to the 2n-th vertical lines, the area of
the (2n+1)-th to the 3n-th vertical lines, and the area of the
(3n+1)-th to the 4n-th vertical lines are black displayed in
sequence one by one every N frames.
[0479] Then, in this example, the black display area selection
circuit 241 is constructed to output the lighting control signals
SG1 to SG4 so that the first fluorescent lamp is turned off when
the area of the first to the n-th vertical lines is black
displayed, the second fluorescent lamp is turned off when the area
of the (n+1)-th to the 2n-th vertical lines is black displayed, the
third fluorescent lamp is turned off when the area of the (2n+1)-th
to the 3n-th vertical lines is black displayed, and the fourth
fluorescent lamp is turned off when the area of the (3n+1)-th to
the 4n-th vertical lines are black displayed.
[0480] As stated above, according to the example 7-3, since the
black picture plane can be displayed in the four divided screen
areas in the horizontal direction in sequence one by one every N
frames, even if the vertical alignment mode color liquid crystal
display panel 201 is included, the alignment of the liquid crystal
of the whole screen can be made uniform, and the holding type
afterimage can be cancelled. Accordingly, the high quality image
display can be carried out.
[0481] Besides, since the fluorescent tubes provided
correspondingly to the black-displayed screen areas can be turned
off by the lighting control signals SG1 to SG4 outputted by the
black display area selection circuit 241, it is possible to avoid
perceptually recognizing the black display picture plane.
Incidentally, also in the case where the black picture plane is
displayed on the color liquid crystal display panel 201 by the
control of the black display control part 233, the backlight 202A
may keep the lighting state.
[0482] Incidentally, in the example 7-1 to the example 7-3,
although the whole area or partial area of the screen is black
displayed in one frame period every N frames, instead of this, the
whole area or partial area of the screen may be black displayed in
several continuous frame periods every N frames.
[0483] As described above, according to this embodiment, since the
screen can be black displayed by the black display control part at
the time of the driving of the liquid crystal display area, the
alignment of the liquid crystal can be made uniform, and even in
the case where the vertical aligned liquid crystal display area is
included, the holding type afterimage is made not to easily occur,
and the high quality image display can be carried out.
[0484] As described above, according to the invention, it is
possible to realize the illumination device in which while the drop
of the display brightness is suppressed, the movement blurring and
the tailing phenomenon in the motion picture display can be
reduced, and the liquid crystal display device using the same.
[0485] Besides, according to the invention, it is possible to
realize the illumination device which can suppress consumed
electric power and in which the device can be made to be small and
light and to have long lifetime, and the liquid crystal display
device using the same.
* * * * *
References