U.S. patent application number 13/231226 was filed with the patent office on 2012-01-05 for planar illumination device and liquid crystal display device using the same.
Invention is credited to Tatsuo Itoh, Takayuki NAGATA, Kazuhisa Yamamoto.
Application Number | 20120002136 13/231226 |
Document ID | / |
Family ID | 39229975 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120002136 |
Kind Code |
A1 |
NAGATA; Takayuki ; et
al. |
January 5, 2012 |
PLANAR ILLUMINATION DEVICE AND LIQUID CRYSTAL DISPLAY DEVICE USING
THE SAME
Abstract
A planar illumination device for illuminating a liquid crystal
display panel provided with a polarizing plate on a light incident
side, includes: a light source unit for emitting light having a
specified polarization direction; and a light irradiating member
for deflecting light emitted from the light source unit and
irradiating the liquid crystal display panel with the deflected
light, wherein the light irradiating member deflects the light
emitted from the light source unit such that the polarization
direction of the light emitted from the light source unit
substantially coincides with a transmission axis direction of the
polarizing plate of the liquid crystal display panel.
Inventors: |
NAGATA; Takayuki; (Osaka,
JP) ; Itoh; Tatsuo; (Osaka, JP) ; Yamamoto;
Kazuhisa; (Osaka, JP) |
Family ID: |
39229975 |
Appl. No.: |
13/231226 |
Filed: |
September 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12439435 |
Feb 27, 2009 |
8040458 |
|
|
PCT/JP2007/068053 |
Sep 18, 2007 |
|
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13231226 |
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Current U.S.
Class: |
349/62 ; 362/235;
362/277 |
Current CPC
Class: |
G02F 1/133615 20130101;
G02F 1/133603 20130101; G02B 6/003 20130101; G02B 6/0025 20130101;
G02B 6/0036 20130101; G02B 6/0041 20130101 |
Class at
Publication: |
349/62 ; 362/277;
362/235 |
International
Class: |
G02F 1/13357 20060101
G02F001/13357; F21V 14/06 20060101 F21V014/06; F21V 14/04 20060101
F21V014/04; F21V 14/00 20060101 F21V014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2006 |
JP |
2006-260226 |
Oct 16, 2006 |
JP |
2006-281082 |
Claims
1. A planar illumination device that illuminates a liquid crystal
display panel, comprising: a light source unit that emits light
toward the liquid crystal display panel; an optical element that is
disposed on an optical path of the light emitted from the light
source unit; and a driver that drives the optical element, wherein
the driver drives the optical element to control a direction of the
light that illuminates the liquid crystal display panel.
2. The planar illumination device according to claim 1, wherein the
optical element includes a lens, and the driver moves a position of
the lens to control the direction of the light that illuminates the
liquid crystal display panel.
3. The planar illumination device according to claim 2, wherein the
optical element includes a lens array as the lens.
4. The planar illumination device according to claim 1, wherein the
optical element includes a mirror, and the driver rotates the
mirror to change an incident angle of light incident on the mirror
to control the direction of the light that illuminates the liquid
crystal display panel.
5. The planar illumination device according to claim 1, further
comprising a human detection sensor that detects a position of a
user, wherein the driver drives the optical element based on a
detection result of the human detection sensor to control the
direction of the light that illuminates the liquid crystal display
panel.
6. The planar illumination device according to claim 1, wherein the
light source unit includes a plurality of LED devices which are
arranged side by side.
7. A liquid crystal display device, comprising: the planar
illumination device according to claim 1; and a liquid crystal
display panel that is illuminated by the planar illumination
device.
Description
[0001] This is a Rule 1.53(b) Divisional of application Ser. No.
12/439,435, which is the National Stage of International
Application No. PCT/JP2007/068053, filed Sep. 18, 2007.
FIELD OF TECHNOLOGY
[0002] The present invention relates to a planar illumination
device suitable as a backlight of a thin flat display used in a
television set or the like, and a liquid crystal display device
using the same.
DESCRIPTION OF THE BACKGROUND ART
[0003] Conventionally, backlight illumination devices utilizing a
cold cathode fluorescent tube have been widely used in liquid
crystal display devices using liquid crystal display panels. In
recent years, attention has been focused on backlight illumination
devices using three color light emitting diodes (LED devices) of
red, green and blue lights for the reproduction of more clear and
natural color tones, and the development thereof has been
vigorously promoted.
[0004] A planar illumination device of the lateral light source
type so-called edge light type in which light from a light source
is incident through a side surface (light incident surface) of a
light guide plate and light is emitted from one principal surface
(light output surface) of the light guide plate for illumination is
used as a backlight illumination device with a relatively small
size. On the other hand, a direct illumination device in which
cathode fluorescent tubes or LED devices are arranged in a planar
manner is used for backlight illumination requiring a large size
and a high luminance.
[0005] A demand for liquid crystal display devices with thin and
large screens such as wall mounted TVs is thought to increase in
the future. However, in order to realize this, direct illumination
devices have a problem of being difficult to be thinned and edge
light type illumination devices using conventional light sources
have a problem of being unable to ensure a sufficient luminance if
screens are large.
[0006] To realize a liquid crystal display device with a thin large
screen, researches have started on an edge light type backlight
using a laser light source, which provides high luminance and which
is suited for a high power output.
[0007] Furthermore, in order to realize a still higher luminance
and lower power consumption, the methods for better utilization of
a backlight illumination has been considered. For example, Patent
Document 1 discloses a method improving the light utilization
efficiency of a liquid crystal display device by providing LEDs
with polarization anisotropy.
[0008] However, the foregoing conventional structure of Patent
Document 1 has the following drawbacks. That is, according to
Patent Document 1, since a light is incident on a light guide plate
from only one direction, a problem of non-uniform luminance is
liable to occur when applied to a large size screen. A problem of
non-uniform color is also liable to occur due to differences in
absorption when three color lights, i.e., red, green and blue
lights propagate in the light guide plate.
[0009] As described above, the enlargement of thin flat displays
represented by plasma displays and liquid crystal displays have
been promoted at a rapid pace in recent years. A direct
illumination device in which cathode fluorescent tubes are arranged
in a planar manner has been conventionally used as a backlight of a
liquid crystal display device requiring a large size and a high
luminance. Power consumption thereof tends to increase
substantially in proportion to the screen size. Furthermore, the
power consumption of the backlight accounts for the large
proportion of the total power consumption of the liquid crystal
display device, and the problem of the power consumption has been a
curtail issue for the liquid crystal display device.
[0010] In recent years, attention has been also focused on
backlight illumination using light emitting diodes (LED devices) of
three primary colors for the reproduction of more clear and natural
color tones. Incidentally, a planar illumination device of the
lateral light source type, a so-called "edge light type" has been
used as a conventional backlight illumination device with a
relatively small size wherein a light emitted from a light source
is incident on the light guide plate through a side surface thereof
and a light is outputted from one principal surface of the light
guide plate to be used for illumination. Here, an attempt has been
made to apply the foregoing edge light type illumination device to
a thin large screen by adopting high-output laser light sources.
However, such applications adopting the light-output laser light
sources have a drawback in that the required power consumption is
larger than that of cathode fluorescent tubes at present, and a
reduction in power consumption is therefore a critical issue.
[0011] In response, various methods have been proposed to realize a
reduction in power consumption. examples of which includes the
method of reducing the power consumption by controlling the
backlight luminance by limiting the maximum luminance of the
backlight, or the method of reducing the power consumption by
improving the utilization of the backlight luminance utilizing
polarized lights (for example, Patent Document 1).
[0012] However, there still exists a strong demand for a reduction
in power consumption, and with the foregoing conventional methods,
the power consumption cannot be reduced to a sufficient level to
meet such demands.
Patent Document 1:
[0013] Japanese Unexamined Patent Publication No. 2006-40639
DISCLOSURE OF THE INVENTION
[0014] An object of the present invention is to provide a planar
illumination device, which realizes a high light utilization
efficiency and low power consumption by improving the transmission
efficiency of a liquid crystal display panel.
[0015] A planar illumination device according to one aspect of the
present invention for illuminating a liquid crystal display panel
provided with a polarizing plate on a light incident side,
includes: a light source unit for emitting light having a specified
polarization direction; and a light irradiating member for
deflecting light emitted from the light source unit and irradiating
the liquid crystal display panel with the deflected light, wherein
the light irradiating member deflects the light emitted from the
light source unit such that the polarization direction of the light
emitted from the light source unit substantially coincides with a
transmission axis direction of the polarizing plate of the liquid
crystal display panel.
[0016] According to the foregoing structure of the planar
illumination device, the liquid crystal display panel is irradiated
with the light emitted from the light source unit in such a manner
that the polarization direction thereof is brought into
substantially coincide with the transmission axis direction of the
liquid crystal display panel. With this structure, the transmission
efficiency of the liquid crystal display panel can be improved,
thereby realizing a light utilization efficiency while reducing
power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a perspective view showing a schematic structure
of a planar illumination device according to the first embodiment
of the invention;
[0018] FIG. 2 is a section showing a schematic structure of a
liquid crystal display panel;
[0019] FIG. 3 is a diagram showing polarized lights of incident
lights and output lights on and from a light guide plate;
[0020] FIGS. 4A and 4B are a rear view and a side view showing a
schematic structure of a planar illumination device according to
the second embodiment of the invention;
[0021] FIG. 5 is a rear view showing a schematic structure of a
planar illumination device according to the third embodiment of the
invention;
[0022] FIG. 6 is a diagram showing polarized lights of incident
lights and output lights on and from a light guide plate used in a
planar illumination device according to the fourth embodiment of
the invention;
[0023] FIG. 7 is a section showing a schematic structure of a light
guide plate used in a planar illumination device according to the
fifth embodiment of the invention;
[0024] FIG. 8A is a perspective view showing a schematic structure
of a light guide plate used in a planar illumination device
according to the sixth embodiment of the invention, FIG. 8B is an
enlarged plan view of a part B of FIG. 8A and FIG. 8C is an
enlarged section of a part A of FIG. 8A;
[0025] FIG. 9 is a perspective view showing a schematic structure
of a reflecting plate used in a planar illumination device
according to the seventh embodiment of the invention;
[0026] FIG. 10A is a perspective view showing a schematic structure
of a display unit of a liquid crystal display device according to
an eighth embodiment of the invention and FIG. 10B is an enlarged
perspective view of a part C of FIG. 10A;
[0027] FIG. 11A is a front view showing the outer appearance of a
liquid crystal display device provided with the display unit of
FIG. 10A, FIG. 11B is a diagram showing a connection relationship
of a human detection sensor, light source units of a backlight and
a controller and FIG. 11C is a block diagram showing a schematic
structure of the controller of FIG. 11B;
[0028] FIGS. 12A and 12B are enlarged perspective views of a light
source unit of a backlight used in a liquid crystal display device
according to a ninth embodiment of the invention;
[0029] FIG. 13 is an enlarged side view of light source units of a
backlight used in a liquid crystal display device according to the
tenth embodiment of the invention;
[0030] FIG. 14 is a perspective view showing a schematic structure
of a display unit of a liquid crystal display device according to
the eleventh embodiment of the invention;
[0031] FIG. 15A is a perspective view showing a schematic structure
of a light guide plate of a backlight used in a liquid crystal
display device according to the twelfth embodiment of the invention
and FIG. 15B is an enlarged plan view of a part D of FIG. 15A;
and
[0032] FIG. 16A is a side view showing a schematic structure of a
backlight used in a liquid crystal display device according to a
thirteenth embodiment of the invention and FIG. 16B is a rear view
of the backlight including a part E of FIG. 16A.
BEST MODES FOR EMBODYING THE INVENTION
[0033] Hereinafter, embodiments of the present invention are
described with reference to the drawings. It should be noted here
that the members having the same structures and the functions are
designated by the same reference numerals, and explanations thereof
may be omitted for convenience for explanations.
First Embodiment
[0034] FIG. 1 is a perspective view showing a schematic structure
of a planar illumination device according to the first embodiment
of the present invention. FIG. 1 shows a liquid crystal display
panel 6 to be illuminated with the planar illumination device of
the present embodiment and prism sheets 4, 5 arranged between the
planar illumination device of the present embodiment and the liquid
crystal display panel 6 in addition to the planar illumination
device of the present embodiment.
[0035] As shown in FIG. 1, the planar illumination device according
to the present embodiment includes linear light source units 1a and
1b, cylindrical lenses 2a and 2b, and a light guide plate 3. The
linear light source unit 1a includes two laser light sources
arranged in the Y-direction in FIG. 1, and laser lights emitted
from the respective laser light sources are outputted to the
cylindrical lens 2a while being converted into linear lights, for
example, using cylindrical lenses (not shown). The respective laser
light sources of the linear light source unit 1a emit lights of
three primary colors, i.e., red, green and blue lights. The linear
light source unit 1b includes three laser light sources arranged in
the X-direction shown in FIG. 1, and laser lights from the
respective laser light sources are emitted to the cylindrical lens
2b while being converted into linear lights, for example, using
unillustrated cylindrical lenses. The respective laser light
sources of the linear light source unit 1a emit lights of three
primary colors, i.e., red, green and blue lights.
[0036] The cylindrical lenses 2a and 2b are made up of Fresnel
lenses, which form lights radially emitted from the linear light
source units 1a and 1b and incident thereon into substantially
parallel lights, and output them to be incident on the light
incident surface of the light guide plate 3. The light guide plate
3 receives lights emitted from the cylindrical lenses 2a and 2b
through the end surface (the light incident surface) thereof, and
outputs them to the liquid crystal display panel 6 from one of the
principal surface thereof. In the light guide plate 3A, a multitude
of isotropic scattering elements having no directivity are formed
uniformly, whereby the incident lights can be equally polarized in
every direction by an optical phenomenon such as reflection,
scattering, refraction or diffraction caused by these scattering
elements. The scattering elements can be realized, for example, by
forming scattering particles made of thermosetting resin or
thermoplastic resin in the light guide plate 3 or generating
bubbles or the like in the light guide plate 3.
[0037] In the present embodiment, the linear light source unit 1a
is arranged so as to emit respective red, green and blue lights as
polarized lights in the Z-direction, whereas the linear light
source unit 1b is arranged so as to emit respective red, green and
blue lights as polarized lights in the X-direction. In this
example, the laser light sources are used for the linear light
source units 1a and 1b. However, the present embodiment is not
intended to be limited to this structure, and for example, LED
devices which emit lights of three primary colors, i.e., red, green
and blue lights may be used as the light sources. In this case,
lights emitted from the LED devices may be polarized in the similar
manner as the laser lights, for example, using polarizing
elements.
[0038] FIG. 2 shows a schematic structure of the liquid crystal
display panel 6. The liquid crystal display panel 6 has such a
general structure that transparent electrodes (not shown) and
liquid crystal molecules 63 are formed between glass substrates 61
and 62. Further, the polarizing plate 64 and the polarizing plate
65 having different transmission axes are formed on the light
output side and the right incident side respectively, so as to
sandwich the glass substrates 61 and 62. The transmission axes of
the polarizing plates 64 and 65 are substantially orthogonal to
each other. The transmission axis of the polarizing plate 65 at the
light incident side extends in the X-direction.
[0039] According to the planar illumination device of the present
embodiment, Z-direction polarized lights as emitted from the linear
light source unit 1a are formed into substantially parallel lights
in an XY plane by the cylindrical lens 2a, and are guided to the
light guide plate 3. On the other hand, X-direction polarized
lights emitted from the linear light source unit 1b are converted
into substantially parallel lights in an XY plane by the
cylindrical lens 2b, and are guided to the light guide plate 3.
[0040] The lights entered into the light guide plate 3 are
polarized by the scattering elements formed in the light guide
plate 3, and are outputted from the light guide plate 3. Here,
since the scattering elements are formed uniformly in the light
guide plate 3, it is possible to output uniform lights from the
light guide plate 3 by inputting thereto substantially parallel
lights. According to the foregoing structure of the present
embodiment, since the lights are entered into the light guide plate
3 from two directions orthogonal to each other, it is possible to
output more uniform lights.
[0041] The lights outputted from the light guide plate 3 are
incident on the liquid crystal display panel 6 after passing
through the prism sheets 4 and 5. The prism sheet 4 polarizes an
output angle in the X-direction, whereas the prism sheet 5
polarizes an output angle in the Y-direction. Accordingly, the
lights emitted from the light guide plate 3 are incident on the
liquid crystal display panel 6 after having an output angle
distribution in the X-direction corrected by the prism sheet 4 and
having an output angle distribution in the Y-direction corrected by
the prism sheet 5.
[0042] With the conventional planar illumination device using
cathode tubes or LEDs, since the lights incident on the liquid
crystal display panel are not polarized, an amount of lights
passing through a polarizing plate on the light incident side of a
liquid crystal display panel becomes 1/2 of the total amount of
incident lights. In contrast, according to the planar illumination
device of the present embodiment, most of the lights outputted from
the light guide plate 3 pass through the polarizing plate 65 on the
incident side of the liquid crystal display panel 6, for the
reasons explained below.
[0043] FIG. 3 is a typical depiction showing polarized lights of
incident lights on and output lights from the light guide plate 3.
In FIG. 3, a light emitted from the linear light source unit 1a is
incident on the light guide plate 3 through a light incident
surface 3a thereof and light emitted from the linear light source
unit 1b is incident on the light guide plate 3 through the light
incident surface 3b of the light guide plate 3, and both of the
incident lights are outputted from the light output source 3c of
the light guide plate 3. The two light incident surfaces 3a and 3b
of the light guide plate 3 are provided so as to be orthogonal to
each other.
[0044] As shown in FIG. 3, the lights respectively entered in the
light guide plate 3 through the light incident surfaces 3a and 3b
are polarized as being reflected or refracted by scattering
elements 7, and are outputted from the light output surface 3c.
[0045] Here, since the scattering elements 7 are formed in a shape
without having any directivity, the lights entered from the
X-direction and the Y-direction propagate toward the light output
surface 3c with equal efficiency and most of lights are outputted
while maintaining the polarization directions. It was confirmed
also with the actual measurement that at least 80% of output light
maintain their original polarization components when polarized
light parallel to or vertical to a light output surface is incident
on the end surface of the foregoing light guide plate containing
scattering elements.
[0046] Accordingly, in the present embodiment, most of the
Z-direction polarized lights entered through the light incident
surface 3a become output lights having polarization planes in an XZ
plane, most of the X-direction polarized lights entered through the
light incident surface 3b become output lights polarized in the
X-direction.
[0047] Since the X-direction polarized lights are not influenced in
the prism sheets 4 and 5, the majority of the lights emitted from
the light guide plate 3 pass through the polarizing plate 65 at the
incident side of the liquid crystal display panel 6 which has the
transmission axis in the X-direction. Assumed based on the actual
measurement that at least 80% of the lights pass, the transmission
efficiency can be improved 1.6 times as high as before.
[0048] As described above, according to the planar illumination
device of the present embodiment, uniform luminance can be obtained
over a large area and higher image quality is promoted by making
lights incident on the light guide plate 3 from the two directions
orthogonal to each other, and the polarizations of lights outputted
from the light guide plate 3 can be aligned and the transmission
efficiency of the liquid crystal display panel 6 can be improved by
specifying incident polarized lights corresponding to the light
incident surfaces of the light guide plate 3. As a result, a liquid
crystal display device of lower power consumption can be
realized.
Second Embodiment
[0049] Next, the second embodiment of the present invention is
described. In the foregoing first embodiment, the linear light
source units 1a and 1b are provided in the outside of the light
guide plate 3 as shown in FIG. 1. In the present invention, a light
source unit is arranged on the underside of the light guide plate 3
and lights are incident on the light guide plate 3 while being
polarized by mirrors or the like. FIGS. 4A and 4B are a rear view
and a side view respectively showing a schematic structure of a
planar illumination device according to the present embodiment.
[0050] As shown in FIGS. 4A and 4B, the planar illumination device
according to the present embodiment includes a light source unit
11, a half wave plate 12, a polarizing beam splitter 13,
linearization optical elements 14a and 14b, prisms 15a and 15b and
the light guide plate 3. The light source unit 11 combines and
outputs lights having aligned polarizations from laser light
sources 11a for three primary colors, and the half wave plate 12
rotates the polarizations of these lights emitted from the light
source unit 11. The linearization optical elements 14a and 14b are
made up or lenticular lenses, cylindrical lenses or the like, and
the prisms 15a and 15b are provided for guiding the lights from the
linearization optical elements 14a and 14b to the light guide plate
3. To these linearization optical elements 14a and 14b, cylindrical
lenses which convert lights into parallel luminous fluxes are
connected.
[0051] According to the planar illumination device of the present
embodiment, lights emitted from the light source unit 11 are
converted into polarized light having a polarization plane
substantially at 45.degree. with respect to the light output
surface 3c of the light guide plate 3 by the half wave plate 12,
and are output from the polarization beam splitter 13 after being
split into P-polarized transmission light and S-polarized reflected
light substantially at a ratio of 1:1 by the polarization beam
splitter 13. The light having passed through or reflected from the
polarization beam splitter 13 is expanded in a plane substantially
parallel to the light guide plate 3 by the linearization optical
element 14a or 14b and converted into parallel luminous flux by the
prism 15a or 15b to be incident on the light guide plate 3.
[0052] According to the planar illumination device of the present
embodiment, it is possible to generate linearly polarized light in
any arbitrary direction and to freely change the transmission to
reflection ratio by the polarization beam splitter 13 by adjusting
the optical axis of the half wave plate 12.
Third Embodiment
[0053] Next, the third embodiment of the present invention is
described. The present embodiment differs from the foregoing second
embodiment in that a light emitted from the light source unit 11 is
guided to the underside of the light guide plate 3 using an optical
fiber 3. FIG. 5 is a rear view showing a schematic structure of a
planar illumination device according to the present embodiment.
[0054] As shown in FIG. 5, the planar illumination device according
to the present embodiment includes a light source unit 11,
collimator lenses 16 and 18, an optical fiber 17, a polarization
beam splitter 13, linearization optical elements 14a and 14b,
prisms 15a and 15b and a light guide plate.
[0055] In the planar illumination device according to the present
embodiment, light from the light source unit 11 is condensed by the
collimator lens 16 to be incident on the optical fiber 17 and light
emitted from the optical fiber 17 is formed into substantially
parallel light by the collimator lens 18 to be incident on the
polarization beam splitter 13. Since the light directed through the
optical fiber 17 loses its polarized nature while being guided by
the optical fiber 17, it is polarized and split into transmission
light and reflected light substantially at 1:1 by the polarization
beam splitter 13.
Fourth Embodiment
[0056] Next, the fourth embodiment of the present invention is
described. In the foregoing first to third embodiments, lights
emitted from the light source unit are entered through two light
incident surfaces of the light guide plate, which are provided to
be orthogonal to one another. In contrast, lights emitted from a
light source unit are incident through three light incident
surfaces of the light guide plate in the present embodiment. FIG. 6
is a typical depiction showing polarized lights of incident lights
on and output lights from a light guide plate used in a planar
illumination device according to the present embodiment. The basic
structures of the present invention are the same as those of the
first through third embodiments, and explanations thereof shall be
omitted here.
[0057] In FIG. 6, lights entered through the light incident surface
3a and a surface facing the light incident surface 3a are
Z-direction polarized lights, and lights entered through the light
incident surface 3b are polarized in the X-direction. Accordingly,
in the present embodiment, the lights entered through the light
incident surface 3a and the surface facing the light incident
surface 3a are outputted as lights having polarization planes in an
XZ plane, whereas the X-direction polarized light entered through
the light incident surface 3b are outputted as X-direction
polarized light. As a result, the output lights of more uniform
luminance can be realized.
[0058] In the present embodiment, it is possible to realize still
more uniform luminance of the output lights by arranging such that
lights are entered also through the surface facing the light
incident surface 3b. In this case, it may be arranged so as to
enter the X-direction polarized lights through the surface facing
the light incident surface 3b and to output the X-direction
polarized lights.
[0059] The effect of improving the light utilization efficiency can
be achieved also from the foregoing structure of illuminating in
three or four directions as in the case of illuminating in two
directions. In this case, it may be arranged such that the lights
entered through the surface facing the light incident surface 3a
have a polarization plane in the XZ-plane and lights entered
through the surface facing the light incident surface 3b become
X-direction polarized light, so that output lights thereof can pass
through the polarizing plate 65 on the incident side of the liquid
crystal display panel. As described, with the arrangement wherein
the lights are entered through a plurality of end surfaces (light
incident surfaces) of the light guide plate, it is possible to
realize a still more uniform luminance.
[0060] Incidentally, the present embodiment may be arranged such
that red, blue and green lights are respectively entered through
different light incident surfaces. For example, in the case of
using SHG as a green light source, only the green light source has
a large size. It is therefore possible to increase the degree of
freedom in arrangement by providing a separate light incident
surface for the green light. Furthermore, in the case of adopting a
screen with difference in length between vertical and horizontal
dimensions, such as 16:9, for example, the problem of
non-uniformity in color due to differences in absorption in the
light guide plate is incident only from the vertical direction.
Fifth Embodiment
[0061] Next, the fifth embodiment of the present invention is
described. In the present embodiment, a polarization hologram layer
is arranged at a reflecting surface side of the light guide plate
according to any one of the foregoing first to fourth embodiments.
Other than the foregoing, the structure of the present invention is
the same as those of the first to fourth embodiments, and
explanations thereof shall be omitted here. FIG. 7 is a
cross-sectional view showing the schematic structure of the light
guide plate used in the planar illumination device according to the
present embodiment.
[0062] In the present embodiment, the lights entered into the light
guide plate 3 are gradually emitted from the light output surface
by being polarized by scattering elements 7 while being
repetitively reflected between one principal surface (light output
surface) and the other principal surface (reflecting surface) of
the light guide plate 3. The present embodiment is the same as the
foregoing first to fourth embodiments in this point; however, the
characteristic feature of the present embodiment lies in that the
light guide plate 3 of the present embodiment particularly includes
a polarization hologram layer 32 formed on a reflecting layer 33 on
the reflecting surface side of the light guide plate 3 as shown in
FIG. 7.
[0063] The polarization hologram layer 32 of the present embodiment
is provided for changing the polarized state of light propagating
in the light guide plate 3 to set the polarization direction of the
light in the X-direction, i.e., the same direction as a
transmission axis of a polarizing plate 65 of the liquid crystal
display panel 6. With this structure, the polarizations of lights
output from the light guide plate 3 can be more aligned, thereby
realizing a still higher transmission efficiency of the liquid
crystal display panel 6.
[0064] In the foregoing embodiment, the polarization hologram layer
32 is provided on the reflecting surface side of the light guide
plate 3. However, the present invention is not intended to be
limited to the foregoing structure, and the polarization hologram
layer may be formed on the light output surface side of the light
guide plate 3 or both on the reflecting surface and the light
output surface.
Sixth Embodiment
[0065] Next, the sixth embodiment of the present invention is
described. In the present embodiment, a plurality of deflectors
having a fine convexo-concave structure is formed on a reflecting
surface in replace of the scattering elements formed in the light
guide plates of the foregoing first to fourth embodiments.
Explanations on other structures of the present invention which are
in common with the foregoing first to fourth embodiments shall be
omitted here. FIG. 8A is a perspective view showing a schematic
structure of the light guide plate used in the planar illumination
device according to the present embodiment, FIG. 8B is an enlarged
plan view of a part B of FIG. 8A, and FIG. 8C is an enlarged
section of a part A of FIG. 8A.
[0066] In a light guide plate 8 of the present embodiment, as shown
in FIGS. 8A and 8C, convexo-concave structures for diffracting,
refracting or scattering incident lights in a thickness direction
(Z-direction in FIG. 8) of the light guide plate 8 are formed on
light incident surfaces 8a and 8b, on which lights from light
sources are incident. On the other hand, a plurality of deflectors
9 having a fine convexo-concave structure for changing propagation
directions of lights incident on the light guide plate 8 by an
optical phenomenon such as reflection, scattering, refraction or
diffraction are formed on the surface (reflecting surface) facing
the output surface of the light guide plate 8 as shown in FIG. 8B.
Each deflector 9 is formed to have a reflecting surface whose
normal lies in the XZ plane or YZ plane and deflects light incident
on the light guide plate 8 to direct it toward the light output
surface. The deflectors 9 may be formed by grooves formed in the
reflecting surface of the light guide plate 8 by laser processing
or grooves integrally formed simultaneously with the molding of the
light guide plate 8.
[0067] In the planar illumination device according to the present
embodiment, for example, lights emitted from the linear light
source units 1a and 1b of FIG. 1 are entered into the light guide
plate 8, wherein the Z-polarized light is entered through the light
incident surface 8a and the X-polarized light is entered through
the light incident surface 8b. The light entered through the light
incident surface 8a is scattered in the Z-direction by the
convexo-concave structure of the light incident surface 8a and
deflected by reflecting surfaces 9a, whose normal lie in XZ planes,
of the deflectors 9 arranged on the reflecting surface to be
emitted from the light output surface as X-direction polarized
light.
[0068] Similarly, the light entered through the light incident
surface 8b is scattered in the Z-direction by the convexo-concave
structure of the light incident surface 8b and deflected by
reflecting surfaces 9b, whose normals lie in the YZ-planes, of the
deflectors 9 arranged on the reflecting surface to be emitted from
the light output surface as the X-direction polarized light.
[0069] The light outputted from the light guide plate 8 is incident
on the liquid crystal display panel 6 after having an output angle
distribution corrected by a prism sheet, and most of this light
passes through a polarizing plate 65 provided on the incident side
so as to have a transmission axis in the X-direction.
[0070] According to the light guide plate of the present
embodiment, the transmission efficiency of the liquid crystal
display panel can be improved by aligning the polarizations of
lights emitted from the planar illumination device and a liquid
crystal display device with low power consumption can be
realized.
[0071] Incidentally, the structure wherein the lights are incident
on the light guide plate from a plurality of directions is the same
as those of the foregoing first to fourth embodiments, and an
improved image quality can be realized by making the luminance
uniform.
Seventh Embodiment
[0072] Next, the seventh embodiment of the present invention is
described. In the present embodiment, a reflecting plate is
provided in replace of the light guide plate of the foregoing sixth
embodiment. Explanations on other structures of the present
invention which are in common with the foregoing sixth embodiment
shall be omitted here. FIG. 9 is a perspective view showing a
schematic structure of a reflecting plate used in a planar
illumination device according to the present embodiment.
[0073] As shown in FIG. 9, a plurality of deflectors 91 having a
fine convexo-concave structure for changing propagation directions
of lights incident from light sources by an optical phenomenon such
as reflection, scattering, refraction or diffraction are arranged
on a reflecting surface 81 of the present embodiment.
[0074] In the planar illumination device according to the present
embodiment, for example, lights from the linear light source units
1a and 1b are directed to the light guide plate 81, wherein the
Z-polarized light is incident from the linear light source unit 1a
and the X-polarized light is incident from the linear light source
unit 1b. The light incident from the linear light source unit 1a is
deflected by reflecting surfaces 91a, whose normals lie in the
XZ-planes, of the deflectors 91 arranged on the reflecting surface
81 to be outputted to the liquid crystal display panel 6 as the
X-direction polarized light while propagating in the air on the
side of the liquid crystal display panel 6 of the reflecting
plate.
[0075] Similarly, the light incident from the linear light source
unit 1b is deflected by reflecting surfaces 91b, whose normals lie
in the YZ-planes, of the deflectors 91 arranged on the reflecting
surface 81 to be outputted to the liquid crystal display panel 6 as
the light polarized in the X-direction light while propagating in
the air on the side of the reflecting surface 81 toward the liquid
crystal display panel 6.
[0076] By adopting the reflecting plate 81 of the present
embodiment, the transmission efficiency of the liquid crystal
display panel can be improved by aligning the polarizations of
lights emitted from the planar illumination device and a liquid
crystal display device with low power consumption can be realized
similar to the foregoing sixth embodiment. Furthermore, higher
image quality can be promoted by making the luminance uniform.
[0077] According to the planar illumination devices and the liquid
crystal display devices using the same according to the first to
seventh embodiments of the present invention, it is possible to
realize wide color reproducibility and thin large screens by
adopting laser light sources, which provides high color purity, and
which is suited for a high power output. It is also possible to
realize large effects of improving image quality resulting from
more uniform luminance, and reducing power consumption resulting
from an improved utilization efficiency of light.
Eighth Embodiment
[0078] Next, the eighth embodiment of the present invention is
described. FIG. 10A is a perspective view showing a schematic
structure of a display unit of a liquid crystal display device
according to the eighth embodiment of the invention and FIG. 10B is
an enlarged perspective view of a part C of FIG. 10A.
[0079] As shown in FIG. 10A, the display unit of the liquid crystal
display device according to the present embodiment includes: a
direct illumination type backlight 101 in which LED devices of
three primary colors for emitting red, blue and green lights are
arranged in a planar manner, a diffusing plate 102 and a liquid
crystal display panel 103. As shown in FIG. 10B, the backlight 101
includes light source units 101a, 101b and 101c in each of which
the LED devices are arranged.
[0080] According to the backlight 101 of the present embodiment,
the LED devices of the light source unit 101a are inclined so as to
emit lights to the left hand side, the LED devices of the light
source unit 101c are inclined so as to emit lights to the right
hand side, and the LED devices of the light source unit 101b are
arranged so as to emit lights to be front side.
[0081] With reference to FIGS. 11A to 11C, a basic operation of the
liquid crystal display device according to the present embodiment
is described below. FIG. 11A is a front view showing the outer
appearance of a liquid crystal display device 104 according to the
present embodiment. FIG. 11B is a typical depiction showing a
connection relationship of a human detection sensor 105 of FIG.
11A, the light source units 101a, 101b and 101c of the backlight
101 and a controller 106 for controlling the respective light
source units 101a, 101b and 101c. FIG. 11C is a block diagram
showing a schematic structure of the controller 106 of FIG.
11B.
[0082] As shown in FIG. 11A, the liquid crystal display device 104
according to the present embodiment is provided with the human
detection sensor 105 for detecting the position of a user 123
watching videos displayed on the liquid crystal display panel 103
of the display unit of the liquid crystal display device 104. The
human detection sensor 105 utilizes, for example, electromagnetic
waves for the position detection of the user 123. Electromagnetic
waves generated from the human detection sensor 105 may be
reflected from the user 123 and then the reflected electromagnetic
waves may be detected by the human detection sensor 105.
[0083] As shown in FIG. 11B, the light source units 101a, 101b and
101c according to the present embodiment are controlled by the
controller 106 connected to the human detection sensor 105. The
controller 106 includes a user position determining section 1061
and an illumination condition setting section 1062 as shown in FIG.
11C. The user position determining section 1061 obtains position
indicative information of the user 123 detected by the human
detection sensor 105 and determines a positional relationship of
the liquid crystal display device 104 and the user 123 based on the
position indicative information. The illumination condition setting
section 1062 sets illumination conditions of the light source units
101a, 101b and 101c based on the determination result of the user
position determining section 1061. Here, the illumination condition
setting sections 1062 sets respective amounts of lights to be
emitted from the light source units 101a, 101b and 101c for
illumination conditions, and the light in an amount as set for each
of the illumination conditions is emitted from each of these light
source units 101a, 101b and 101c.
[0084] In the liquid crystal display device 104 according to the
present embodiment, lights emitted from the respective light source
units 101a, 101b and 101c of the backlight 1 have transmittances of
the respective colors of red, blue and green controlled in the
liquid crystal display panel 103 after being diffused by the
diffusing plate 102, and an image is color displayed on the front
surface of the liquid crystal display panel 103.
[0085] Here, the luminance of an image displayed on the liquid
crystal panel 103 varies according to a viewing angle of the user
123 (hereinafter referred to as "viewing angle characteristic").
Normally, the luminance is highest when viewed from the front face,
and the luminance becomes lower as the viewing angle is displaced
from the front face. However, since the LED devices are inclined in
the light source units 101a and 101c of the present embodiment, the
viewing angle characteristic of only lights emitted from the light
source unit 101a has a skewed luminance distribution to the left
from the front of the screen, and lights emitted only from the
light source unit 101c have a viewing angle characteristic with a
distribution opposite to that of the lights emitted from the light
source unit 101a.
[0086] Next, an operation of controlling an amount of light by the
controller 106 is described. The user 123 shown in FIG. 11A is
located more to the right side with respect to the front side of
the screen of the liquid crystal display device 104. Firstly, the
human detection sensor 105 detects the user 123 positioned more to
the right with respect to the front side of the screen of the
liquid crystal display device 104 and transmits this information to
the controller 106. Based on this information, the user position
determining section 1061 determines that the user 123 is positioned
more to the right with respect to the front side of the screen of
the liquid crystal display device 104 and sends the result of
determination to the illumination condition setting section 1062.
The illumination condition setting section 1062 sets the emission
amounts of the respective light source units 101a, 101b and 101c
such that the amount of light emitted from the light source unit
101c is larger than those of the light source units 101a and 101b.
Specifically, the illumination condition setting section 1062 sets
the respective illumination conditions to increase the amount of
light emitted from the light source unit 101c and to decrease the
amounts of lights emitted from the light source units 101a and
101b. With the foregoing light amount control by the controller
106, the luminance at a line-of-sight angle from the right side of
the screen increases to increase visibility for the user 123 and
luminance at other angles decrease to reduce power consumption.
[0087] According to the liquid crystal display device of the
present embodiment, the position of the user 123 is detected and
the luminance is controlled to increase in that direction, and the
visibility is improved and the power consumption is reduced by
decreasing the luminance in other directions.
[0088] Generally, differences in viewing angle characteristics
among the respective colors if any, cause a problem in that color
changes according to viewing angles. In response, the present
embodiment has a desirable structure wherein fine adjustments can
be made on the amounts of lights in respective colors emitted at a
plurality of output angles, thereby displaying a quality image with
a wide viewing angle while reducing variations in color.
[0089] In the present embodiment, the position of the user 123 is
detected by the human detection sensor 105. However, the present
embodiment is not intended to be limited to this, and, for example,
the user 123 may set his position using a remote controller or the
like.
[0090] In the present embodiment, the viewing angle characteristic
of the backlight 101 is controlled according to the direction
toward the user 123. However, the present embodiment is not
intended to be limited to this, and for example, the luminance of
the backlight 101 may be adjusted as well according to distance
between the user 123 and the liquid crystal display device 104. For
example, when the user 123 is positioned in a vicinity of the
liquid crystal display device 104, a reduction in power consumption
can be realized by reducing the luminance in the direction toward
the user 123.
[0091] In the case where a plurality of users are present around
the liquid crystal display device, power saving can be promoted by
controlling the viewing angles in accordance with the positions of
the users. Furthermore, by detecting the position of the user 123
in a predetermined cycle, a light amount control in conformity with
the movement of the user 123 can be realized.
Ninth Embodiment
[0092] Next, the ninth embodiment of the present invention is
described. The characteristic structure of the present embodiment
lies in the backlight 101 of the foregoing eighth embodiment, which
will be explained below. Explanations on other structures of the
present invention which are in common with the foregoing eighth
embodiment shall be omitted here. FIGS. 12A and 12B are enlarged
perspective views of a light source unit of a backlight used in a
liquid crystal display device according to the present
embodiment.
[0093] As shown in FIG. 12A, the backlight of the present
embodiment is arranged such that a light source unit 101d made up
of LED devices arranged in a planar manner emits lights to the
front face, and a lens array 107 corresponding to the respective
LED devices is provided. The position of the lens array 107 is
controlled on a plane.
[0094] Specifically, the position of the lens array 107 is
controlled by a lens array driver 124 for moving the lens array
107. This lens array driver 124 moves the lens array 107 in
accordance with an illumination condition as set by an illumination
condition setting section 1062.
[0095] Here, FIG. 12A shows a case where lights are emitted toward
the front side of the light source unit 101d and FIG. 12B shows a
case where lights are emitted toward the right side of the light
source unit 101d. In FIG. 12B, emission directions of the lights
are changed by displacing the lens array 107 in a direction of "a"
from the position of FIG. 12A. According to the foregoing
structure, it is possible to make a fine adjustment of the emission
direction, thereby realizing the effects as achieved from the
foregoing eighth embodiment.
[0096] According to the foregoing structure, the viewing angle can
be adjusted by moving the lens array 107 in an optical axis
direction.
[0097] Furthermore, according to the present embodiment, both a
light source unit with a fixed emission direction and a light
source unit with a variable emission direction may be used as the
light source units of the backlight.
Tenth Embodiment
[0098] Next, the tenth embodiment of the present invention is
described. The present embodiment also has the characteristic
structure in the backlight 101 of the foregoing eighth embodiment.
Explanations on other structures of the present invention which are
in common with the foregoing eighth embodiment shall be omitted
here. FIG. 13 is an enlarged side view of a light source unit of a
backlight used in a liquid crystal display device according to the
present embodiment.
[0099] As shown in FIG. 13, the backlight of the present embodiment
is arranged such that lights emitted from a light source unit 101e
are reflected from mirrors 108, and emission directions are
controlled by changing the angles of the mirrors 108 by rotating
the mirrors 108 in directions "b". The rotation of the mirrors 108
is controlled by a mirror driver 125 for rotating the mirrors 108,
and the mirror driver 125 rotates the mirrors 108 in accordance
with an illumination condition set by an illumination condition
setting section 1062.
[0100] In the present embodiment, both a light source unit with a
fixed emission direction and a light source unit with a variable
emission direction may be used as the light source units of the
backlight.
Eleventh Embodiment
[0101] Next, the eleventh embodiment of the present invention is
described. In the present embodiment, an edge light type backlight
is adopted in replace of the direct illumination type backlight of
the foregoing eighth embodiment. Explanations on other structures
of the present invention which are in common with the above eighth
embodiment shall be omitted here. FIG. 14 is a perspective view
showing a schematic structure of a display unit of a liquid crystal
display device according to the present embodiment.
[0102] A display unit of the liquid crystal display device
according to the present embodiment is, as shown in FIG. 14,
provided with an edge light type backlight 111, a prism sheet 115
and a liquid crystal display panel 103. The backlight 111 includes
light source units 112a, 112b and 112c made up of LED devices or
laser light sources for emitting lights of three primary colors,
i.e. red, green and blue lights, and a light guide plate 113. As in
the structure of the first embodiment, a multitude of isotropic
scattering elements 114 having no directivity are uniformly
arranged in the light guide plate 113, and incident lights from the
light source units 112a, 112b and 112c are equally deflected in
every direction by an optical phenomenon such as reflection,
scattering, refraction or diffraction caused by the multitude of
scattering elements 114. The prism sheet 115 is the one for
deflecting output angles in the Y-direction of FIG. 14.
[0103] Although not shown, the backlight 111 of the present
embodiment is installed in a liquid crystal display device similar
to that of the above eighth embodiment and is arranged such that
amounts of light emitted from the light source units 112a, 112b and
112c can be controlled based on the information from a human
detection sensor. Specifically, the backlight 111 of the present
embodiment includes an emission amount adjuster 126 for adjusting
the amounts of lights respectively emitted from the light source
units 112a, 112b and 112c, and the emission amount adjuster 126
adjusts the amounts of lights emitted in accordance with the
illumination conditions set by the illumination condition setting
section 1062.
[0104] In the liquid crystal display device according to the
present embodiment, lights emitted from the light source units
112a, 112b and 112c are incident on the light guide plate 113 and
deflected by the scattering elements 114 in the light guide plate
113 to be emitted from the light guide plate 113. Here, since the
majority of the lights incident on the light guide plate 113 are
emitted while being biased in a direction opposite to incident
directions, the viewing angle characteristic of light emitted from
the light source unit 112a has a maximum luminance in a negative
direction along an X axis of FIG. 14 and light emitted from the
light source unit 112c is opposite to the light emitted from the
light source unit 112a. Furthermore, the light emitted from the
light source unit 112b has a viewing angle characteristic biased in
the Y direction of FIG. 14; however, comes to have a viewing angle
characteristic with a maximum luminance to the front side of the
backlight by having an output angle thereof deflected by the prism
sheet 115.
[0105] The lights emitted from the light source units 112a and 112c
and passed through the prism sheet 115 and the light from the light
source unit 112b deflected by the prism sheet 115 have the
transmittances of the respective colors of red, blue and green
controlled in the liquid crystal display panel 103, thereby
displaying a color image on the front surface of the liquid crystal
display panel 103.
[0106] Here, in the case where a user is positioned, for example,
more to the right (positive direction of an X axis of FIG. 14) with
respect to the front side of the screen of the liquid crystal
display panel, the human detection sensor 105 detects the user 123
located more to the right with respect to the front side of the
screen of the liquid crystal display device 104 and this
information is sent to the controller 106. Subsequently, based on
this information, a user position determining section 1061
determines that the user 123 is located more to the right than the
front side of the screen of the liquid crystal display device 104
and sends the result of determination to the illumination condition
setting section 1062. The illumination condition setting section
1062 sets the respective emission quantities of the light source
units 112a, 112b and 112c such that the amount of lights emitted
from the light source unit 112c is larger than those of the light
source units 112a and 112b. Specifically, the illumination
condition setting section 1062 sets the respective illumination
conditions to increase the amount of light emitted from the light
source unit 112c and to decrease the amounts of lights emitted from
the light source units 112a and 112b. The emission amount adjuster
126 adjusts the respective amounts of lights emitted from the light
source units 112a and 112b in accordance with the illumination
conditions set by the illumination condition setting section 1062.
With the foregoing emission amount control of the emission amount
adjuster 126, the luminance at a line-of-sight angle from the right
side of the screen increases to increase visibility for the user
123 and luminances at other angles decrease, thereby suppressing
power consumption.
[0107] Also in the liquid crystal display device of the present
embodiment, the position of the user is detected and the luminance
is controlled to increase in that direction, and visibility is
improved and power consumption is reduced by decreasing luminance
in other directions.
[0108] When using a laser light source as a light source, the
effect of increasing the luminance in a necessary direction and
decreasing it in an unwanted direction is further improved since
the directivity is higher as compared with the case of LED devices.
In this case, if the directivity of laser lights in the light guide
plate 113 is too high, the range of an output angle of light
emitted from the light guide plate 113 can be widened to obtain the
output light with a suitable degree of scattering by providing a
convexo-concave structure for diffracting, refracting or scattering
light in a thickness direction on the light incident surface of the
light guide plate 113.
Twelfth Embodiment
[0109] Next, the twelfth embodiment of the present invention is
described. In the present embodiment, a plurality of deflectors
having a fine convexo-concave structure are arranged on the
reflecting surface in replace of the scattering elements provided
in the light guide plate of the foregoing eleventh embodiment.
Explanations on other structures of the present invention which are
in common with the foregoing eleventh embodiment shall be omitted
here. FIG. 15A is a perspective view showing the schematic
structure of a light guide plate used in a liquid crystal display
device according to the present embodiment and FIG. 15B is an
enlarged plan view of a part D of FIG. 15A.
[0110] As shown in FIGS. 15A and 15B, a plurality of deflectors 117
having such a fine convexo-concave structure for deflecting and
emitting lights incident through different end surfaces in
different directions are arranged on a surface (reflecting surface)
facing a light output surface in a light guide plate 116 of the
present embodiment.
[0111] In the liquid crystal display device according to the
present embodiment, light source units 112a, 112b and 112c are
semiconductor laser devices and lights with high directivity are
incident while being suitably diffused by the convexo-concave
structures of the respective light incident surfaces of the light
guide plate 116. Each deflector 117 on the reflecting surface of
the light guide plate 116 is formed to have a reflecting surface
whose normal lies in an XZ plane or YZ plane, and lights incident
from the light source units 112a, 112b and 112c are emitted in
different directions in the XZ plane. Thus, effects similar to
those of the above eleventh embodiment are obtained.
Thirteenth Embodiment
[0112] Next, the thirteenth embodiment of the present invention is
described. In the foregoing eleventh and twelfth embodiments, the
light source units are provided in the outside of the light guide
plate. In contrast, in the present embodiment, light source units
are provided on the underside of a light guide plate and lights are
incident on the light guide plate while being deflected by mirrors
or the like. FIG. 16A is a side view showing a schematic structure
of a backlight 111 according to the present embodiment and FIG. 16B
is a rear view of the backlight including a part E of FIG. 16A.
[0113] The backlight 111 of the present embodiment is, as shown in
FIGS. 16A and 16b, provided with a light guide plate 113, two light
source units 119a and 119b arranged on the underside of the light
guide plate 113 for combining and emitting lights with aligned
polarizations from laser light sources of three primary colors,
prisms 118a, 118b and 118c for introducing lights from the light
source units 119a and 119b on the underside of the light guide
plate 113 to end surfaces of the light guide plate 113, half wave
plates 120a and 120b for rotating the polarizations of the lights
from the light source units 119a and 119b, polarization beam
splitters 121a and 121b, and linearization optical elements 122a,
122b and 122c which are lenticular lenses, cylindrical lenses or
the like. The orientations of the optical axes of the half wave
plates 120a and 120b are controlled by a half wave plate optical
axis adjuster 127, so that the polarizations of the lights from the
light source units 119a and 119b can be controlled. The half wave
plate optical axis adjuster 127 changes the orientations of the
optical axes of the half wave plates 120a and 120b in accordance
with illumination conditions set by an illumination condition
setting section 1062.
[0114] Since the polarizations of lights emitted from the light
source units 119a and 119b can be freely changed by the two wave
plates 120a and 120b in the backlight 111 of the present
embodiment, ratios of lights passing through and reflected from the
polarization beam splitters 121a and 121b can be controlled.
[0115] According to the foregoing structure, lights incident on the
light guide plate 113 via the linearization optical elements 122a,
122b and 122c and the prisms 118, 118b and 118c have different
output angles depending on the end surfaces on which they are
incident, and amounts of light thereof can be controlled
individually. As a result, the effects as achieved from the
foregoing eleventh and twelfth embodiments can be achieved.
[0116] According to the liquid crystal display devices of the
eighth to the thirteenth embodiments of the present invention, it
is possible to obtain a large effect of reducing power consumption
by reducing the luminance in unnecessary directions in which the
user is not present while ensuring sufficient luminance in a
necessary direction by detecting the position of the user.
[0117] Furthermore, by suppressing changes in color when the screen
is viewed in an oblique direction, a liquid crystal display device
with a high viewing angle and high image quality can be
realized.
[0118] The present invention is summarized as follows from the
above respective embodiments. Specifically, a planar illumination
device according to one aspect of the present invention for
illuminating a liquid crystal display panel provided with a
polarizing plate on a light incident side, includes: a light source
unit for emitting light having a specified polarization direction;
and a light irradiating member for deflecting light emitted from
the light source unit and irradiating the liquid crystal display
panel with the deflected light, wherein the light irradiating
member deflects the light emitted from the light source unit such
that the polarization direction of the light emitted from the light
source unit substantially coincides with a transmission axis
direction of the polarizing plate of the liquid crystal display
panel.
[0119] According to the foregoing structure of the planar
illumination device, the liquid crystal display panel is irradiated
with the light emitted from the light source unit in such a manner
that the polarization direction thereof is brought into
substantially coincide with the transmission axis direction of the
liquid crystal display panel. With this structure, the transmission
efficiency of the liquid crystal display panel can be improved,
thereby realizing improved light utilization efficiency while
reducing power consumption.
[0120] It is preferable that the light source unit includes either
a first light source for emitting light having a polarization
direction substantially orthogonal to a surface of the polarizing
plate to be incident on the light irradiating member in the
transmission axis direction of the polarizing plate or a second
light source for emitting light having a polarization direction
substantially parallel to the surface of the polarizing plate to be
incident on the light irradiating member in a direction orthogonal
to the transmission axis direction of the polarizing plate. It is
also preferable that the light source includes the first light
source and the second light source; and lights from the first and
second light sources are incident on the light irradiating member
in directions orthogonal to each other.
[0121] According to the foregoing structure, the polarization
directions of the respective lights emitted from the first and
second light sources can be brought into substantially coincide
with the transmission axis direction of the polarizing plate of the
liquid crystal display panel.
[0122] With the foregoing structure, it is preferable that the
light irradiating member be a light guide plate having a first end
surface substantially vertical to a transmission axis of the
polarizing plate, a second end surface orthogonal to the first end
surface, a first principal surface from which incident lights
through the first and second end surfaces are emitted, and a second
principal surface facing the first principal surface.
[0123] According to the foregoing structure, the lights emitted
from the first and second light sources can be incident through the
two orthogonal end surfaces and the liquid crystal display panel
can be irradiated with the respective emitted lights having the
polarization directions thereof brought into substantially coincide
with the transmission axis direction of the liquid crystal display
panel. It is therefore possible to realize a uniform luminance of a
liquid crystal display panel with a large area and to display an
image of an improved quality.
[0124] The light guide plate preferably includes therein a
plurality of isotropic scattering elements for deflecting the
respective lights emitted from the first and second light
sources.
[0125] According to the foregoing structure, the respective lights
emitted from the first and second light sources can be equally
scattered in every direction within the light guide plate. It is
therefore possible to direct the respective lights emitted from the
first and second light sources respectively to the first principal
surface at substantially the same efficiency.
[0126] It is preferable that the plurality of scattering elements
be formed within the light guide plate at uniform intensities.
[0127] According to the foregoing structure, the scattering
elements are distributed within the light guide plate at uniform
density. It is therefore possible to direct the respective lights
emitted from the first and second light sources respectively to the
first principal surface at the same efficiency.
[0128] It is preferable that a plurality of fine members for
deflecting the respective lights emitted from the first and second
light sources in directions toward the first principal surface are
formed on the second principal surface of the light guide plate;
each of the plurality of fine members has a first reflecting
surface having a normal in a virtual plane vertical to the first
principal surface and orthogonal to the first end surface and a
second reflecting surface having a normal in a virtual plane
vertical to the first principal surface and orthogonal to the
second end surface; and the first and second reflecting surfaces
reflect the lights respectively emitted from the first and second
light sources toward the first principal surface.
[0129] According to the foregoing structure, since the respective
lights emitted from the first and second light sources are
reflected from the first and second reflecting surfaces toward the
first principal surface. It is therefore possible to make the
efficiency of directing the light emitted from the first light
source to the first principle surface more equal to the efficiency
of directing the light emitted from the second light source to the
first principle surface.
[0130] It is preferable that the plurality of fine members have the
same shape and are periodically formed on the second principal
surface.
[0131] According to the foregoing structure, the plurality of fine
members in the same shape are periodically distributed on the
second principal surface. It is therefore possible to make it
closer to one another the respective efficiencies of directing the
light emitted from the first light source to the first principle
surface and directing the light emitted from the second light
source to the first principle surface.
[0132] It is preferable that the light guide plate further include
a polarization hologram layer arranged on the second principal
surface and adapted to align the polarization directions of the
respective lights emitted from the first and second light sources
so that the polarization directions of the respective lights
emitted from the first and second light sources substantially
coincide with the transmission axis direction of the liquid crystal
display panel.
[0133] According to the foregoing structure, the polarization
directions of the respective lights emitted from the first and
second light sources can be aligned. It is therefore possible to
make the polarization directions of the respective lights emitted
from the first and second light sources be more approximated to the
transmission axis direction of the liquid crystal display
panel.
[0134] The light irradiating member is preferably the light
irradiating member is a reflecting plate having a flat surface
provided on a side of the liquid crystal display panel, a first
side substantially vertical to the transmission axis direction of
the polarizing plate and a second side orthogonal to the first side
and adapted to reflect the respective lights emitted from the first
and second light sources on the flat surface to be outputted to the
side of the liquid crystal display panel.
[0135] According to the foregoing structure, it is possible to
simplify the structure of the light irradiating member.
[0136] It is preferable that a plurality of fine members for
deflecting the respective lights emitted from the first and second
light sources in directions to the side of the liquid crystal
display panel are formed on the flat surface; each of the plurality
of fine members has a first reflecting surface having a normal in a
virtual plane vertical to the flat surface and orthogonal to the
first side and a second reflecting surface having a normal in a
virtual plane vertical to the flat surface and orthogonal to the
second side; and the first and second reflecting surfaces reflect
the lights emitted from the first and second light sources toward
the liquid crystal display panel.
[0137] According to the foregoing structure, the respective lights
emitted from the first and second light sources can be reflected
from the first and second reflecting surfaces toward the first
principal surface. It is therefore possible to make the
polarization directions of the respective lights emitted from the
first and second light sources be more approximated to the
transmission axis direction of the liquid crystal display
panel.
[0138] It is preferable that the plurality of fine members have the
same shape and periodically formed on the second principal
surface.
[0139] According to the foregoing structure, the plurality of fine
members in the same shape are periodically distributed on the plane
on the side of the liquid crystal display panel. It is therefore
possible to make it closer to one another the respective
efficiencies of directing the light emitted from the first light
source to the first principle surface and directing the light
emitted from the second light source to the first principle
surface.
[0140] It is preferable to further include: a half wave plate for
rotating the polarization direction of light emitted from the light
source unit; and a polarization beam splitter for splitting the
light having passed through the half wave plate into first and
second polarization components, transmitting light of the first
polarization component and reflecting light of the second
polarization component, wherein the polarization beam splitter is
provided so as to face the second principal surface of the light
guide plate and emits either one of the lights of the first and
second polarization components as a light emitted from the first
light source while emitting the other as a light emitted from the
second light source.
[0141] According to the foregoing structure, a light emitted from
one light source unit can be split into a light emitted from the
first light source and a light emitted from the second light
source. It is therefore possible to reduce the number of the light
source units. Furthermore, the polarization beam splitter for
splitting the light emitted from one light source unit is provided
so as to face the second principal surface of the light guide
plate. It is therefore possible to prevent an increase in size of
the device.
[0142] It is preferable to further include a lightguide for guiding
light emitted from the light source unit; and a polarization beam
splitter for splitting the light guided by the light guide into
first and second polarization components, transmitting light of the
first polarization component and reflecting light of the second
polarization component; wherein the polarization beam splitter is
provided so as to face the second principal surface of the light
guide plate and emits either one of the lights of the first and
second polarization components as a light emitted from the first
light source while emitting the other as a light emitted from the
second light source.
[0143] According to the foregoing structure, lights emitted from
one light source unit can be split and emitted as the light emitted
from the first light source and the light emitted from the second
light source. It is therefore possible to emit two lights without
increasing the number of the light source unit. Furthermore, the
polarization beam splitter for splitting the light emitted from one
light source unit is provided so as to face the second principal
surface of the light guide plate. It is therefore possible to
prevent an increase in size of the device.
[0144] It is preferable that either one of the first and second
light sources emit a green light; and the other one of the first
and second light sources emits red and blue lights.
[0145] According to the foregoing structure, even if the size of
the light source for emitting green light is larger than that of
the light source for emitting red and blue lights, a degree of
freedom in arranging the light sources can be increased since an
end surface on which the green light is incident is provided
independently of an end surface on which the red and blue lights
are incident.
[0146] It is preferable that either one of the first and second
light sources emit a blue light; and the blue light is emitted in a
direction substantially parallel to the shorter one of two sides of
the first principal surface orthogonal to each other.
[0147] According to the foregoing structure, a traveling distance
of the blue light in the light guide plate can be made shorter. It
is therefore possible to reduce the attenuation of blue light power
in the light guide plate.
[0148] The light source unit is preferably a laser light source
unit.
[0149] According to the foregoing structure, the polarized nature
of the light emitted from the light source unit can be intensified.
It is therefore possible to more approximate the polarization
direction of light emitted from the light source unit to the
transmission axis direction of the liquid crystal display
panel.
[0150] The light source unit preferably includes LED devices and a
polarizing element for polarizing lights emitted from the LED
devices in a predetermined direction.
[0151] According to the foregoing structure, the light having a
specified polarization direction can be emitted using inexpensive
LED devices. It is therefore possible to reduce the cost of the
light source unit.
[0152] It is preferable to further include a controller for
controlling the half wave plate, wherein the controller changes a
ratio of the lights of the first and second polarization components
split by the polarization beam splitter by rotating the
polarization direction of the light emitted from the light source
unit using the half wave plate.
[0153] According to the foregoing structure, the polarization
directions of the lights emitted from the light source unit can be
freely changed. It is therefore possible to control the ratio of
the lights of the first and second polarization components split by
the polarization beam splitter.
[0154] A liquid crystal display device according to another aspect
of the present invention comprises the above planar illumination
device and a liquid crystal display panel to be illuminated by the
planar illumination device, wherein a polarization direction of
light irradiated from the planar illumination device substantially
coincides with a transmission axis of the polarizing plate.
[0155] According to the foregoing structure of the liquid crystal
display device, the transmission efficiency of the liquid crystal
display panel can be increased by irradiating the liquid crystal
display panel with the light emitted from the light source unit and
having the polarization direction thereof brought into
substantially coincide with the transmission axis direction of the
liquid crystal display panel. It is therefore possible to realize a
liquid crystal display device with high light utilization
efficiency and low power consumption.
[0156] It is preferable to further include a sensor for detecting
the position of a user viewing an image displayed on the liquid
crystal display panel and an adjuster for adjusting an amount of
light emitted from the light source unit based on the detection
result by the sensor.
[0157] With the foregoing structure, the amount of light emitted
from the light source unit can be so adjusted as to improve
visibility for the user in accordance with the position of the
user.
INDUSTRIAL APPLICABILITY
[0158] A planar illumination device and a liquid crystal display
device using the same according to the present invention can
realize, a thin large screen with wide color reproducibility and
can realize a liquid crystal display device with high image quality
and low power consumption by uniformizing the luminance of the
planar illumination device and improving light utilization
efficiency, wherefore they are useful in the display field.
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