U.S. patent application number 12/433966 was filed with the patent office on 2009-08-27 for display device.
This patent application is currently assigned to MITSUBISHI DENKI KABUSHIKI KAISHA. Invention is credited to Atsushi Ito, Tomohiro Sasagawa, Toshiyuki Yoneda, Akimasa Yuuki, Nobuyuki Zumoto.
Application Number | 20090213299 12/433966 |
Document ID | / |
Family ID | 36595195 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090213299 |
Kind Code |
A1 |
Ito; Atsushi ; et
al. |
August 27, 2009 |
DISPLAY DEVICE
Abstract
A display device includes a light guide plate which includes a
light transmission portion and an antireflection portion at two
opposite end faces and which is provided with a light extraction
portion in part of a surface, respective light sources which are
arranged on outer sides of the two opposite end faces, a
transmission liquid crystal panel located adjacent to the light
extraction portion, and a synchronous drive unit that alternately
turns ON the light sources and that displays an image that is
synchronous with an alternating turn-ON operation of the
transmission liquid crystal panel.
Inventors: |
Ito; Atsushi; (Tokyo,
JP) ; Yuuki; Akimasa; (Tokyo, JP) ; Zumoto;
Nobuyuki; (Tokyo, JP) ; Yoneda; Toshiyuki;
(Tokyo, JP) ; Sasagawa; Tomohiro; (Tokyo,
JP) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
700 THIRTEENTH ST. NW, SUITE 300
WASHINGTON
DC
20005-3960
US
|
Assignee: |
MITSUBISHI DENKI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
36595195 |
Appl. No.: |
12/433966 |
Filed: |
May 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11243452 |
Oct 5, 2005 |
|
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12433966 |
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Current U.S.
Class: |
349/65 |
Current CPC
Class: |
G02F 1/133615
20130101 |
Class at
Publication: |
349/65 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2004 |
JP |
2004-371431 |
Claims
1-14. (canceled)
15. A display device comprising: a light guide plate including
first and second transparent plates, each of the first and second
transparent plates including first and second opposed end faces, a
light transmission portion at the first end face, an antireflection
portion at the second end face, and a light extraction surface
transverse to the first and second end faces, the first and second
transparent plates being placed one over the other so that the
light extraction surfaces are oriented in the same direction and so
that the light transmission portions at the first end faces are at
opposite sides of the light guide plate; first and second light
sources respectively located opposite the light transmission
portions at the first end faces of the first and second transparent
plates; a transmission liquid crystal panel located adjacent to the
light extraction surface of one of the first and second transparent
plates; and a synchronous drive unit that alternately turns on and
off the first and second light sources so that an image is
displayed on the liquid crystal display panel and is synchronous
with alternating turn turning on and turning off of the
transmission liquid crystal panel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to display devices, and more
particularly to a display device which is capable of presenting a
stereoscopic display or simultaneously displaying two different
images in separate angular directions, and which is used for an
information equipment terminal.
[0003] 2. Description of the Related Art
[0004] In a prior-art display device which is capable of
stereoscopic display or two-screen display (in which two different
images are simultaneously displayed in separate angular
directions), a pair of light sources are arranged in the vicinities
of both the end faces of a light guide plate whose surface is
formed with a light extraction portion having a directionality in
the emergent angle of light, by a roughening work or the like, and
the light extraction portion is overlaid with a dual-side prism
sheet and a transmission type liquid crystal panel, wherein the
pair of light sources are alternately turned ON, and two different
images are displayed on the transmission type liquid crystal panel
in synchronism with the alternate turn-ON operations, thereby to
present the stereoscopic display or two-image display (refer to,
for, example, T. Sasagawa, et al.: "Dual Directional Backlight for
Stereoscopic LCD", P1-P3, Society for Information Display '03
DIGEST (2003)).
[0005] The light guide plate of the prior-art stereoscopic display
device or the prior-art display device displaying the two images in
the separate angular directions, is constructed as stated above.
Therefore, in light outputted from the light source at one end,
light except direct light which emerges in a luminous intensity
distribution for one image, from the light extraction portion in
consequence of light guide, arrives at the other end and is
reflected into reflection light which is guided in the opposite
direction. When the reflection light emerges from the light
extraction portion, it comes to have a luminous intensity
distribution for the other image, and hence, the two images are
observed in superposition. This has resulted in the problem that
the contrast of the stereoscopic image or two different images
lower.
SUMMARY OF THE INVENTION
[0006] This invention has been made in order to solve the problem
as stated above, and provides a display device which can enhance
the contrast of stereoscopic image or two different images with
uniform luminous intensity distributions maintained.
[0007] A display device according to this invention includes a
light guide plate which includes light transmission portions and
antireflection portions at both its end faces, and which is
provided with a light extraction portion in part of its surface, a
pair of light sources which are arranged on outer sides of both the
end faces, a transmission type liquid crystal panel which is
arranged in adjacency to the light extraction portion, and a
synchronous drive unit that alternately turns ON the pair of light
sources so as to display images synchronous with the alternate
turn-ON operations, on the transmission type liquid crystal
panel.
[0008] Besides, a display device according to this invention
includes a light guide plate which includes antireflection portions
at both its end faces, which includes hole arrays inside both the
end faces, and which is provided with a light extraction portion in
part of its surface, a pair of light sources which are inserted in
the hole arrays, a transmission type liquid crystal panel which is
arranged in adjacency to the light extraction portion, and a
synchronous drive unit that alternately turns ON the pair of light
sources so as to display images synchronous with the alternate
turn-ON operations, on the transmission type liquid crystal
panel.
[0009] Besides, a display device according to this invention
includes a light guide plate which includes two transparent plates,
each being such that one of both end faces of the transparent plate
is a light transmission portion, while the other is an
antireflection portion, and that a light extraction portion is
provided in part of a surface of the transparent plate, the
transparent plates being placed one over the other so that the
light extraction portions may be held in the same sense, and that
the light transmission portions may lie oppositely to each other, a
pair of light sources which are arranged on outer sides of the
light transmission portions, a transmission type liquid crystal
panel which is arranged in adjacency to one of the light extraction
portions, and a synchronous drive unit that alternately turns ON
the pair of light sources so as to display images synchronous with
the alternate turn-ON operations, on the transmission type liquid
crystal panel.
[0010] Further, a display device according to this invention
includes a light guide plate which is provided with a light
extraction portion in part of its surface, a pair of light sources
which are arranged on outer sides of both end faces of the light
guide plate, a light reflection member which is arranged in the
vicinity of that surface of the light guide plate which is opposite
to the surface provided with the light extraction portion, and in a
manner to define gaps serving as antireflection portions, between
the light reflection member and both the end faces, a transmission
type liquid crystal panel which is arranged in adjacency to the
light extraction portion, and a synchronous drive unit that
alternately turns ON the pair of light sources so as to display
images synchronous with the alternate turn-ON operations, on the
transmission type liquid crystal panel.
[0011] According to this invention, antireflection portions are
provided at parts other than light transmission portions, whereby
reflection light ascribable to the retrocession of light inputted
from one end after being reflected from the other end can be
reduced, and the contrast of a display image can be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an explanatory diagram for explaining the
propagation of light within a light guide plate according to this
invention;
[0013] FIG. 2 is a model diagram of a display device in Embodiment
1 of the invention;
[0014] FIGS. 3A and 3B are graphs showing the distribution of
luminous intensities from a light extraction portion as well as a
prism sheet according to this invention;
[0015] FIG. 4 is a perspective view of the display device in
Embodiment 1 of the invention;
[0016] FIG. 5 is a top view of a light guide plate in Embodiment 1
of the invention;
[0017] FIG. 6 is a model diagram of a display device in Embodiment
2 of the invention;
[0018] FIG. 7 is a model diagram of a light emitting diode in
Embodiment 2 of the invention;
[0019] FIG. 8 is a top view of a light guide plate in Embodiment 2
of the invention;
[0020] FIG. 9 is a model diagram of a display device in Embodiment
3 of the invention;
[0021] FIG. 10 is a model diagram of a display device in Embodiment
4 of the invention;
[0022] FIG. 11 is a characteristic diagram in Embodiment 4 of the
invention;
[0023] FIG. 12 is a model diagram of a display device in Embodiment
5 of the invention;
[0024] FIG. 13 is a top view of a light guide plate in Embodiment 5
of the invention;
[0025] FIG. 14 is a partial enlarged perspective view of a light
guide plate in Embodiment 6 of the invention;
[0026] FIG. 15 is a top view of a light guide plate in Embodiment 7
of the invention;
[0027] FIG. 16 is a model diagram of a display device in Embodiment
8 of the invention;
[0028] FIG. 17 is a model diagram of a light guide plate in
Embodiment 8 of the invention;
[0029] FIG. 18 is a characteristic diagram in Embodiment 8 of the
invention;
[0030] FIG. 19 is a partial sectional view of the light guide plate
in Embodiment 8 of the invention; and
[0031] FIGS. 20A and 20B are explanatory diagrams in Embodiment 9
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
[0032] Hereinafter, an embodiment of the present invention will be
described with reference to the drawings. The inventors have found
out that, in view of the operating principles of a two-image
display, the prevention of reflection from the end face of a light
guide plate is an effective expedient as elucidated below.
[0033] In a case where light has been inputted from one light
source to the light guide plate, the luminance distribution of
light emergent from a light extraction portion can be computed as
stated below, from the situation of light propagating within the
light guide plate, and so on. FIG. 1 is an explanatory diagram for
explaining the propagation of light within the light guide plate in
a configuration in which a pair of light sources are arranged on
the outer sides of both the end faces of the light guide plate 2.
Referring to FIG. 1, it is assumed that only the light source 1b of
the pair of light sources 1a and 1b is turned ON. I1 denotes the
propagation intensity of light near the light input end of the
light guide plate 2 as seen from the light source 1b, I2 denotes
the propagation intensity of light in the middle of the light guide
plate, and I3 denotes the propagation intensity of light near the
reflection end of the light guide plate. A mean reflection factor
at the reflection end is denoted by R. Regarding the light
extraction efficiencies of the light extraction portion 2a provided
in the light guide plate 2, t1 denotes the light extraction
efficiency near the light input end of the light guide plate, t2
denotes the light extraction efficiency in the middle, and t3
denotes the light extraction efficiency near the reflection end.
Regarding luminances based on light beams as which the direct light
propagating within the light guide plate 2 leftward from the light
source 1b is extracted from the light extraction portion 2a, .phi.1
denotes the luminance near the light input end of the light guide
plate, .phi.2 denotes the luminance in the middle, and .phi.3
denotes the luminance near the reflection end. Regarding
propagation light intensities in the case where reflection light
reflected at the reflection end of the light guide plate propagates
rightward, I'1 denotes the light intensity near the light input
end, I'2 denotes the light intensity in the middle, and I'3 denotes
the light intensity near the reflection end. Further, regarding
luminances based on light beams as which the reflection light is
extracted from the light extraction portion 2a, .phi.'1 denotes the
luminance near the light input end of the light guide plate,
.phi.'2 denotes the luminance in the middle, and .phi.'3 denotes
the luminance near the reflection end.
[0034] The ratio between the luminance based on the direct light
and the luminance based on the reflection light in the lights
extracted from the light extraction portion 2a is defined as the
contrast of the light guide plate. C1 denotes the contrast at the
light input end, C2 denotes the contrast in the middle, and C3
denotes the contrast at the light output end. Luminance of the
direct light: .phi.n=tn.times.In where n=1, 2, 3
Luminance of the reflection light: .phi.'n=tn.times.I'n Propagation
intensity of the reflection light: I'3=R.times.I3 Besides, the
propagation intensities at both the ends of the light guide plate
are computed from the symmetry of the procession and retrocession
of light, as follows:
I'1=I'3.times.I3/I1=R.times.I3.times.I3/I1
I'2=I'3.times.I3/I2=R.times.I3.times.I3/I2
The contrast is computed as follows:
Cn = .phi. n / .phi. ' n = tn .times. In / ( tn .times. I ' n ) =
In / I ' n ##EQU00001##
That is,
[0035] C1=(I1/I3).sup.2/R (1)
C2=(I2/I3).sup.2/R (2)
C3=1/R (3)
Alternatively, in terms of the light extraction efficiencies,
C1=((.phi.1/.phi.3)(t3/t1))2/R (4)
C2=((.phi.2/.phi.3)(t3/t2))2/R (5)
C3=1/R (6)
[0036] It is understood from the above computational formulas that
the contrast Cn and the reflection factor R at the reflection end
of the light guide plate are in inversely proportional
relationships at all the positions of the light guide plate, and
that the reflection factor R must be reduced in order to enhance
the contrast. On the other hand, to set t3>t1 and t3>t2 in
the formulas (4)-(6) is a condition under which the contrast is
enhanced on the whole surface of the light guide plate without
resorting to the reduction of the reflection factor R. However, the
light guide plate of a stereoscopic display device using the pair
of light sources must have symmetric optical characteristics for
the respective lights from the pair of light sources, that is, it
must hold t3=t1, so that the condition of setting t3>t1 and
t3>t2 cannot be adopted.
[0037] Also, to set .phi.3<.phi.1 or .phi.3<.phi.2 is a
condition under which the contrast is enhanced on the whole surface
of the light guide plate without resorting to the reduction of the
reflection factor R. Under this condition, however, the luminance
distribution becomes nonuniform, and the symmetry condition of
.phi.3=.phi.1 is not met, so that the condition cannot be adopted.
For the above reasons, the reflection factor R needs to be reduced
for the enhancement of the contrast.
[0038] FIG. 2 is a model diagram for explaining a display device in
Embodiment 1 for carrying out this invention. Referring to FIG. 2,
pairs of light sources 1a and 1b are arranged in the vicinities of
both the end faces of a light guide plate 2. Lights outputted from
the light sources 1a or 1b propagate within the light guide plate
2, and they are extracted onto the side of a transmission type
liquid crystal panel 3 from a light extraction portion 2a disposed
in the surface of the light guide plate 2. The light extraction
portion 2a is constructed by subjecting the surface of the light
guide plate 2 to a roughening work so that light having passed
through this light extraction portion may have a directionality.
FIG. 3A shows the luminous intensity distribution of the light
which is emergent from the light extraction portion 2a when only
the light sources 1a are turned ON. In FIG. 3A, the axis of
abscissas represents that inclination angle of the light guide
plate 2 in which the clockwise inclination angle thereof is taken
in a +direction with the normal direction thereof set at zero
degree, while the axis of ordinates represents a luminance (in
cd/m.sup.2). The light emergent from the light extraction portion
2a passes through the transmission type liquid crystal panel 3
while holding the luminous intensity distribution shown in FIG. 3A,
thereby to become image information. On the other hand, a luminous
intensity distribution in the case where the light sources 1b are
turned ON becomes one which is obtained in such a way that the
luminous intensity distribution in FIG. 3A is inverted in bilateral
symmetry with respect to the position of zero degree. The light
sources 1a and 1b are alternately turned ON by a synchronous drive
unit 4, and two different images are displayed on the transmission
type liquid crystal panel 3 in synchronism with the alternate
turn-ON operations, whereby the two different images can be
simultaneously observed from separate angles. FIG. 4 is a
perspective view showing the arrangement of the light sources 1a
and 1b, the light guide plate 2 and the transmission type liquid
crystal panel 3 in this embodiment. FIG. 5 is a top view in which
the light guide plate 2 and the light sources 1a and 1b in this
embodiment are seen from the side of a display surface. Those parts
of the end faces of the light guide plate 2 to which the light
sources 1a and 1b are vicinal are made of light transmission
portions 21, and the other parts are made of antireflection
portions 22. As the antireflection portions, it is considered to
form, for example, a dielectric multilayer film functioning as an
antireflection film, on the outer side of the end face of the light
guide plate 2. Mentioned as an example of the dielectric multilayer
film is a multilayer film in which the film of tantalum dioxide
being a high refractivity film, and the film of silicon dioxide
being a low refractivity film are alternately deposited.
[0039] The effect of the enhancement of the contrast in this case
is computed as stated below. As regards FIG. 5, denoting by .alpha.
the proportion of the area of those parts of each end face of the
light guide plate which are provided with the antireflection
portions, denoting by (1-.alpha.) the proportion of the area of the
light transmission portions, denoting by R0 the reflection factor
of the whole end face in the case where the end face is not partly
provided with the antireflection portions, and denoting by Re the
reflection factor of the whole end face in the case where the end
face is partly provided with the antireflection portions, the
relationship of a formula indicated below holds:
Re=(1-.alpha.).times.R0(0<.alpha.<1)
[0040] In this embodiment, assuming the area of the antireflection
portions to be, for example, the half of the end face of the light
guide plate, .alpha.=0.5 holds, and Re=0.5.times.R0 is
obtained.
[0041] The contrasts C1, C2 and C3 in this case become as follows,
when contrasts C10, C20 and C30 in the case where the end face is
not provided with the antireflection portions are substituted into
Formulas (1), (2) and (3):
C1=2.times.C10
C2=2.times.C20
C3=2.times.C30
That is, according to the invention, the contrasts can be enhanced
double higher than in the case where any antireflection portion is
not provided over the whole surface of the light guide plate.
[0042] As described above, in this embodiment, those parts of each
end face of the light guide plate which are not vicinal to the
light sources are formed of the antireflection portions as shown in
FIG. 5. Therefore, as to each of the lights for simultaneously
displaying the two different images, the light which has reached
the antireflection portions of the reflection end face opposed to
the input end face has its reflection attenuated, and the display
device capable of two-screen display of high contrast can be
realized.
[0043] Incidentally, although the dielectric multilayer film which
functions as the antireflection film has been exemplified as the
antireflection portions in this embodiment, it is also allowed to
employ another antireflection film, for example, a film which is
coated with the particles of silicon dioxide being a low
refractivity material. Alternatively, since the reflection is
preventable by endowing the antireflection portions with a light
absorbability, it is also allowed to employ a method in which
sheets of high light absorbability are stuck to the antireflection
portions, or a method in which the antireflection portions are
coated with a coating material of high light absorbability.
Embodiment 2
[0044] FIG. 6 is a model diagram for explaining a display device
according to Embodiment 2 for carrying out this invention.
Referring to FIG. 6, both the end faces of a light guide plate 2
are antireflection portions 22, and hole arrays 23a and 23b are
provided inside both the end faces. Pairs of light sources 1a and
1b are such that light emitting diodes (LEDs) are embedded in the
hole arrays 23a and 23b, respectively. Lights outputted from the
light sources 1a or 1b propagate within the light guide plate 2,
and they are extracted onto the side of a transmission type liquid
crystal panel 3 from a light extraction portion 2a disposed in the
surface of the light guide plate 2. The light extraction portion 2a
is constructed by subjecting the surface of the light guide plate 2
to a roughening work so that light having passed through this light
extraction portion may have a directionality. When only the light
sources 1a are turned ON, a luminous intensity distribution shown
in FIG. 3A is established, and when only the light sources 1b are
turned ON, a luminous intensity distribution is established in
which the luminous intensity distribution in FIG. 3A is inverted in
bilateral symmetry with respect to the position of zero degree. The
light emergent from the light extraction portion 2a passes through
the transmission type liquid crystal panel 3 while holding the
luminous intensity distribution as stated above, thereby to become
image information. The light sources 1a and 1b are alternately
turned ON by a synchronous drive unit 4, and two different images
are displayed on the transmission type liquid crystal panel 3 in
synchronism with the alternate turn-ON operations, whereby two
observers who simultaneously observe from separate angles can
recognize the different images, respectively.
[0045] FIG. 7 is a model diagram of an LED which constitutes the
light source 1a or 1b in this embodiment. An LED chip 33 which
emits light of single wavelength is arranged within an LED case 32
whose inner surface is formed with a reflection film 31. The
surroundings of the LED chip 33 are filled up with a light emitting
member 34 by which the light of single wavelength emitted from the
LED chip 33 is converted into white light. The light emitting
member 34 is, for example, one in which a phosphor is dispersed and
mixed in a resin. The LED case 32 is made of a material whose light
absorbability is high. The reflection film 31 serves to prevent the
light emitted from the LED chip 33, from being absorbed by the LED
case 32, and simultaneously to endow the light with a
directionality for the purpose of outputting the light much onto
the inner side of the light guide plate 2.
[0046] FIG. 8 is a top view in which the light guide plate 2 and
the light sources 1a and 1b in this embodiment are seen from the
side of a display surface. Both the end faces of the light guide
plate 2 are the antireflection portions 22. Each of the
antireflection portions 22 is such that a black sheet of high light
absorbability, for example, is stuck on the end face of the light
guide plate 2. As to each of the lights emitted from the light
sources 1a or 1b, the light having reached the opposite end face of
the light guide plate has its reflection light attenuated by the
antireflection portion. Further, also the light having reached the
LED case of each light source 1a or 1b can have its reflection
light attenuated by being absorbed by this LED case which is made
of the material of high light absorbability. As a result, the
unnecessary reflection lights are reduced, and contrast can be
enhanced.
[0047] Incidentally, although the sheet of high light absorbability
has been employed as each antireflection portion in this
embodiment, a coating material of high light absorbability may well
be applied. Alternatively, each antireflection portion may well be
a dielectric multilayer film which functions as an antireflection
film, or a film which is coated with the particles of silicon
dioxide being a low refractivity material. Besides, although the
LED case has been made of the material of high light absorbability,
it may well be replaced with a construction in which the outer
surface of an LED case of low light absorbability is coated with a
light-absorbable coating material. Besides, although the embodiment
has indicated the example in which each LED emitting the light of
single wavelength is combined with the light emitting member in
order to convert the emitted light into the white light, an LED
which emits the white light may well be employed. In this case, the
light emitting member is dispensed with.
Embodiment 3
[0048] FIG. 9 is a model diagram for explaining a display device in
Embodiment 3 for carrying out this invention. As shown in FIG. 9, a
light guide plate 2 in this embodiment is constructed of two
transparent plates 43 and 44, each of which is such that one of the
end faces of the light guide plate is a light transmission portion
45, while the other is an antireflection portion 46. The two
transparent plates 43 and 44 are placed one over the other in such
a manner that light extraction portions 43a and 44a are held in the
same sense, and that the light transmission portions 45 are
opposite to each other. Pairs of light sources 1a and 1b are
arranged on the outer sides of the light transmission portions 45.
The light extraction portion 43a is constructed by subjecting the
surface of the transparent plate 43 to a roughening work so that
lights emitted from the light sources 1a and guided through this
transparent plate 43 may become a luminous intensity distribution
as shown in FIG. 3A. Likewise, the light extraction portion 44a is
constructed by subjecting the surface of the transparent plate 44
to a roughening work so that lights emitted from the light sources
1b and guided through this transparent plate 44 may become a
luminous intensity distribution in which the luminous intensity
distribution in FIG. 3A has been inverted in bilateral symmetry
with respect to the position of zero degree. The light outputted
from the light source 1a or 1b and emergent from the light
extraction portion 43a or 44a passes through a transmission type
liquid crystal panel 3 while holding the luminous intensity
distribution as stated above, thereby to become image information.
A Synchronous drive unit 4 turns ON the light sources 1a and 1b
alternately, and two different images are displayed on the
transmission type liquid crystal panel 3 in synchronism with the
alternate turn-ON operations. Thus, two observers can recognize the
different images by observing them from separate angles,
respectively.
[0049] In this embodiment, the antireflection portions 46 of the
transparent plates 43 and 44 can be formed on the whole end faces,
so that .alpha. used in the case of calculating the effect of the
contrast enhancement in Embodiment 1 described before (that is, the
proportion of the area of the parts where the antireflection
portions are provided) can be set at 1 (one) Therefore, Re=0 holds,
and the contrast becomes infinity in theory and is enhanced 10
times or more in actuality. Moreover, since the light guide plate 2
is separated into the transparent plates 43 and 44 for the
respective light sources in this embodiment, the distributions of
the extraction rates of the light extraction unit in Formulas (4),
(5) and (6) can be designed as t3>t2>t1 independently for the
respective light sources, and hence, the contrast is enhanced still
more.
[0050] Incidentally, as each antireflection portion 46, it is
possible to employ a dielectric multilayer film which functions as
an antireflection film, a film which is coated with the particles
of silicon dioxide being a low refractivity material, a sheet which
has a light absorbability, or a coating film which includes a
coating material of high light absorbability.
Embodiment 4
[0051] FIG. 10 is a model diagram of a display device in Embodiment
4. Referring to FIG. 10, a light reflection member 51 is disposed
in the vicinity of that surface of a light guide plate 2 which is
opposite to the surface thereof provided with a light extraction
portion 2a. The light reflection member 51 is smaller in width than
the light guide plate 2, and gaps 52 are provided between this
light reflection member 51 and both the end faces of the light
guide plate 2. Since each of the gaps 52 has a light reflection
factor lower than that of the light reflection member 51, it
functions as an antireflection portion.
[0052] Owing to such a construction, when part of light outputted
from a light source 1a arranged at one end part has arrived at the
other end part, it is reflected from the other end part to
propagate onto the side of the light sources 1a, but part of the
reflected light is emergent out of the light guide plate 2 through
the gap 52. That is, since the gap 52 is lower in the light
reflection than the light reflection member 51, it functions as the
antireflection portion. FIG. 11 shows a result which has been
obtained by simulating the relationship between the width A of the
gap 52 from the end part and the contrast, when the thickness of
the light guide plate 2 was 1 mm. As seen from FIG. 11, the
contrast is enhanced more as the width A becomes larger. When the
width A enlarges to make the light reflection member 51 narrower
than the region of the light extraction portion 2a, a light beam
quantity for displaying an image as emerges out of the light
extraction portion 2a decreases, and hence, the width A cannot be
made very large.
[0053] Incidentally, although the surface of each gap 52 is not
especially subjected to any treatment in this embodiment, the
contrast is enhanced still more by forming an antireflection film
or a light absorption film on the surface of the gap 52.
Embodiment 5
[0054] FIG. 12 is a model diagram of a display device in Embodiment
5. Referring to FIG. 12, those regions of the end faces of a light
guide plate 2 on which light sources 1a and 1b are not disposed are
formed in the shape of wedges, and antireflection films 62 are
provided on those surfaces of the light guide plate 2 which oppose
to the oblique surfaces of wedge-shaped portions 61. FIG. 13 is a
top view in which the light guide plate 2 and the light sources 1a
and 1b in this embodiment are seen from the side of a display
surface. As shown in an enlarged perspective view, those parts of
both the end faces of the light guide plate 2 on which the light
sources are not disposed are formed in the shape of the wedges, and
the antireflection films 62 are provided at positions opposed to
the oblique surfaces of the wedge-shaped portions 61.
[0055] In this embodiment, in lights outputted from the light
sources 1a or 1b, lights having arrived at the opposite end face of
the light guide plate 2 are mostly radiated out through the
wedge-shaped portions 61, but parts of the lights are reflected
downwardly of the light guide plate 2 at the parts of the oblique
surfaces of the wedge-shaped portions 61, and the reflection lights
are attenuated by the antireflection films 62. As a result, the
unnecessary reflection lights can be reduced, and the contrast of
two-screen display can be enhanced. Denoting by B an angle which is
defined between the wedge-shaped portion 61 and the surface opposed
to the oblique surface of this wedge-shaped portion, the angle B
should preferably be about 45.degree.. When the angle B is greater
than 45.degree., a probability at which the unnecessary reflection
lights return to the light guide plate 2 heightens. Conversely,
when the angle B is smaller than 45.degree., the oblique surfaces
of the wedge-shaped portions 61 lengthen, and the area of the light
extraction portion 2a of the light guide plate 2 needs to be
decreased in some cases.
[0056] Incidentally, each antireflection film 62 may well be
another antireflection film, for example, a film which is coated
with the particles of silicon dioxide being a low refractivity
material. Besides, since the antireflection film 62 may suffice to
have the effect of reducing the reflection of the light, it may
well be changed into a light absorption film. Mentioned as the
light absorption film is, for example, a sheet of high light
absorbability or a coating film of high light absorbability.
[0057] Besides, although the construction in which the light
sources 1a and 1b are arranged so as to confront each other has
been shown in FIG. 13, the light sources 1a or 1b may well be
constructed so as to confront the wedge-shaped portions 61 of the
opposite end parts of the light guide plate 2, respectively.
Embodiment 6
[0058] In Embodiment 5, the part of the oblique surface of each
wedge-shaped portion is formed to be oblong, and hence, it
sometimes intercepts light which is outputted from the light source
arranged in the vicinity of the wedge-shaped portion, and which
spreads in a lateral direction. Therefore, the lights between the
light sources are not sufficiently mixed, and a stripe-shaped
luminance nonuniformity might appear from the position at which the
wedge-shaped portion is arranged. FIG. 14 is the partial enlarged
perspective view of a light guide plate for use in a display device
in Embodiment 6. In this embodiment, the light guide plate 2 having
antireflection portions as shown in FIG. 14 is employed in the same
construction as in Embodiment 5. Referring to FIG. 14, the oblique
surface of each wedge-shaped portion 63 is formed so as to decrease
its area toward the middle of the light guide plate 2, and an
antireflection film 64 is provided at a position opposed to the
oblique surface.
[0059] Owing to such a construction, in lights outputted from the
light sources, lights having arrived at the opposite end face of
the light guide plate 2 are mostly radiated out through the
wedge-shaped portions 63, but parts of the lights are reflected
downwardly of the light guide plate 2 at the parts of the oblique
surfaces of the wedge-shaped portions 63, and the reflection lights
are attenuated by the antireflection films 64. As a result, the
unnecessary reflection lights can be reduced, and the contrast of
two-screen display can be enhanced. Furthermore, the lights which
spread laterally from the light sources arranged in the vicinities
of the wedge-shaped portions 63 are not intercepted by these
wedge-shaped portions 63, and the uniformity of luminances is
enhanced.
Embodiment 7
[0060] FIG. 15 is a top view of a light guide plate 2 for use in a
display device in Embodiment 7. In this embodiment, triangular
light absorption portions 65a and 65b are provided at those
positions of the surface of the light guide plate 2 at which lights
from light sources 1a or 1b located at the end parts of the light
guide plate 2 do not directly arrive, a light extraction portion 2a
being provided in the surface.
[0061] Owing to such a construction, the lights outputted from the
light sources 1a arranged at one end part are absorbed by the light
absorption portions 65b provided at the other end part, and the
lights outputted from the light sources 1b are not absorbed by
these light absorption portions 65b. Therefore, luminances are not
lowered, and contrast is enhanced.
[0062] By the way, in this embodiment, the light absorption
portions 65a and 65b have been formed on the surface in which the
light extraction portion 2a is provided, but they may well be
formed on the surface of the light guide plate 2 opposite to the
surface formed with the light extraction portion 2a, or they may
well be formed on both the surfaces of the light guide plate 2.
Besides, the contrast is enhanced still more by combining this
embodiment with the construction of Embodiment 1.
Embodiment 8
[0063] FIG. 16 is a model diagram of a display device in Embodiment
8. Referring to FIG. 16, recesses 71 of wedge-shaped section are
formed between a light extraction portion 2a provided in the
surface of a light guide plate 2 and the end parts of this light
guide plate. FIG. 17 is a sectional view of the light guide plate 2
in this embodiment. Each of the recesses 71 having the wedge-shaped
section has a length D from the end part of the light guide plate
2, and an angle E is defined between the oblique surface of the
wedge-shaped recess 71 and the surface of the light guide plate
2.
[0064] Owing to such a construction, when part of light outputted
from a light source 1a arranged at one end part of the light guide
plate 2 has arrived at the recess 71 provided at the other end
part, it is radiated out of the light guide plate 2 through the
recess 71. Therefore, in the light outputted from the light source
on one side, the light having is arrived at the opposite end face
of the light guide plate 2 has its reflection reduced, and contrast
can be enhanced.
[0065] FIG. 18 shows results which have been obtained by simulating
a relative light beam quantity extracted from the light extraction
portion 2a and the E-dependency of the contrast in the case of
changing the angle E defined between the oblique surface of each
wedge-shaped portion 71 and the surface of the light guide plate 2,
when the thickness of the light guide plate 2 was 1 mm, and the
length D of each recess 71 was 3 mm. As seen from FIG. 18, the
effect of the contrast enhancement is great in the region of 2-6
degrees in terms of the angle E, but the light beam quantity
decreases at and above 5 degrees in terms of the angle E.
Therefore, the angle E should desirably be 4 degrees or below.
[0066] By the way, in this embodiment, the recesses 71 have been
formed on only that surface side of the light guide plate 2 which
is provided with the light extraction portion 2a, but they may well
be provided in the surface of the light guide plate 2 opposite to
the surface provided with the light extraction portion 2a, or they
may well be provided in both the surfaces of the light guide plate
2. Besides, in this embodiment, each recess 71 of wedge-shaped
section has been formed in a shape having one oblique surface, but
it may well be constructed by forming a plurality of small recesses
of wedge-shaped section as shown in FIG. 19.
[0067] Further, when a light absorption film is deposited on the
oblique surface and vertical surface of each recess 71, it is
possible to prevent a phenomenon in which light radiated out of the
light guide plate 2 is reflected by any other member to enter the
light guide plate 2 again. Therefore, the contrast is enhanced
still more.
Embodiment 9
[0068] The operating principles of Embodiment 9 will be described
with reference to FIGS. 20A and 20B. A display device in the
embodiment of the invention is such that a prism sheet 5 is
arranged between a light extraction portion 2a and a transmission
type liquid crystal panel 3. As shown in FIGS. 20A and 20B, trains
of prisms of triangular section are formed in the surface of the
prism sheet 5 opposed to the light extraction portion 2a, and
trains of lenses of cylindrical section are formed in the surface
thereof opposed to the transmission type liquid crystal panel 3.
The construction of the display device except the arrangement of
the prism sheet 5 is the same as that of the display device
described in Embodiment 1. Each of lights which emerge from the
light extraction unit 2a when only the light sources 1a are turned
ON and which have the luminous intensity distribution as shown in
FIG. 3A, is refracted and reflected within the prism sheet 5 while
passing through this prism sheet 5, and it comes to have a luminous
intensity distribution as shown in FIG. 3B. According to this
luminous intensity distribution, the light exhibits high
intensities within the left range of 0 degree to about -15 degrees
with respect to the front direction of the light guide plate 2, and
it hardly emerges within the right range of 0 degree to about 15
degrees. In FIG. 3B, the axis of abscissas represents that
inclination angle of the surface of the prism sheet 5 opposed to
the transmission type liquid crystal panel 3 in which the clockwise
inclination angle thereof is taken in a +direction with the normal
direction thereof set at zero degree, while the axis of ordinates
represents a luminance (in cd/m.sup.2). The light having the
luminous intensity distribution passes through the transmission
type liquid crystal panel 3 while holding this luminous intensity
distribution. Assuming that an observer exists at a distance of
about 300 mm from the front of the panel 3, and that the interval
between the right eye 6a and left eye 6b of the observer is 65 mm,
an angle which is defined between a straight line connecting the
center of the transmission type liquid crystal panel 3 and the
right eye 6a and the normal direction of the transmission type
liquid crystal panel 3 becomes about 6 degrees. On this occasion,
regarding an image having the luminous intensity distribution as
shown in FIG. 3B, as shown in FIG. 20A, the image can be recognized
by the right eye 6a of the observer, but it is not recognized by
the left eye 6b because the light does not arrive. On the other
hand, when only the light sources 1b are turned ON, it is possible
to display an image in a luminous intensity distribution into which
the luminous intensity distribution shown in FIG. 3B is bilaterally
inverted with respect to zero degree. In this case, as shown in
FIG. 20B, only the left eye 6b can recognize the image, and the
image is not recognized by the right eye 6a. Therefore, in a case
where the light sources 1a and 1b are alternately turned ON by the
synchronous drive unit (not illustrated) and where the right and
left parallactic images are displayed on the transmission type
liquid crystal panel 3 in synchronism with the alternate turn-ON
operations, the observer can recognize the different parallactic
images by the right and left eyes, respectively, and a stereoscopic
vision based on parallax becomes possible.
[0069] In the display device thus constructed, in lights outputted
from the respective light sources for displaying the right and left
parallactic images, lights having arrived at the opposite end faces
of the light guide plate have their reflection lights attenuated by
the antireflection portions. Therefore, the contrasts of the images
can be enhanced, and the clear stereoscopic image is obtained.
[0070] By the way, in this embodiment, the construction except the
arrangement of the prism sheet has been made the same as that of
Embodiment 1, but the same construction as in Embodiment 1 may well
be replaced with the same construction as in any of Embodiments 2
through 4.
* * * * *