U.S. patent application number 09/749658 was filed with the patent office on 2001-06-28 for liquid-crystal display apparatus.
Invention is credited to Yamaguchi, Akira.
Application Number | 20010005243 09/749658 |
Document ID | / |
Family ID | 18502695 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005243 |
Kind Code |
A1 |
Yamaguchi, Akira |
June 28, 2001 |
Liquid-crystal display apparatus
Abstract
The improved liquid-crystal display apparatus has a
liquid-crystal display panel, a backlight section that issues
collimated light launched and a light diffusing plate and satisfies
either the relation p/tan .theta. .ltoreq. L or d.times.tan
.theta..ltoreq. A, or the both relations, where p is the average
pitch of emergence of the collimated light, .theta. is the
divergence angle of the collimated light, L is the distance from
the collimating plate to the interface in the liquid-crystal layer
of the liquid-crystal display panel which is directed to the
collimating plate, d is the distance from the light diffusing plate
to the interface in the liquid-crystal layer of the liquid-crystal
display panel which is directed to the light diffusing plate, and A
is the pixel size of the liquid-crystal display panel. The
apparatus can display images of high contrast and quality over a
wide range of viewing angles without having unevenness and
blur.
Inventors: |
Yamaguchi, Akira; (Kanagawa,
JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Family ID: |
18502695 |
Appl. No.: |
09/749658 |
Filed: |
December 28, 2000 |
Current U.S.
Class: |
349/61 ; 349/113;
349/64 |
Current CPC
Class: |
G02F 1/133602 20130101;
G02F 1/133607 20210101; G02F 1/133504 20130101 |
Class at
Publication: |
349/61 ; 349/64;
349/113 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 1999 |
JP |
11-373750 |
Claims
What is claimed is:
1. A liquid-crystal display apparatus having a liquid-crystal
display panel and a backlight section that uses a collimating plate
to have collimated light launched into said liquid-crystal display
panel, said apparatus satisfying the following relation: p/tan
.theta. .ltoreq. L where p is an average pitch of emergence of said
collimated light, .theta. is a divergence angle of said collimated
light, and L is a distance from said collimating plate to an
interface in a liquid-crystal layer of the liquid-crystal display
panel which is directed to the collimating plate.
2. The liquid-crystal display apparatus according to claim 1,
wherein said backlight section has not only the collimating plate
but also a light source and a lamp housing for accommodating said
light source an inner surface of which is covered with a diffuse
reflecting layer, and said collimating plate has a lens substrate,
a multiple of lenses that are supported on said lens substrate for
collimating incident light, a diffuse reflecting layer that is
formed over the lens substrate except in light entrance areas that
align with an optical axes of said lenses, and a shield layer that
is formed over the lens substrate on a side closer to the lenses
than said diffuse reflecting layer except in said light entrance
areas.
3. The liquid-crystal display apparatus according to claim 1,
wherein a pixel size of said liquid-crystal display panel is no
more than 200 .mu.m.
4. The liquid-crystal display apparatus according to claim 1,
wherein said collimated light has a divergence angle .theta. of no
more than 10.degree..
5. The liquid-crystal display apparatus according to claim 1,
wherein said liquid-crystal display panel is monochromatic.
6. A liquid-crystal display apparatus having a liquid-crystal
display panel, a backlight section that uses a collimating plate to
have collimated light launched into said liquid-crystal display
panel and a light diffusing plate that diffuses the image-bearing
light that has passed through said liquid-crystal display panel,
said apparatus satisfying the following relation: d.times. tan
.theta. .ltoreq. A where .theta. is a divergence angle of said
collimated light, d is a distance from the light diffusing plate to
an interface in a liquid-crystal layer of said liquid-crystal
display panel which is directed to the light diffusing plate, and A
is a pixel size of said liquid-crystal display panel.
7. The liquid-crystal display apparatus according to claim 6,
wherein said backlight section has not only the collimating plate
but also a light source and a lamp housing for accommodating said
light source an inner surface of which is covered with a diffuse
reflecting layer, and said collimating plate has a lens substrate,
a multiple of lenses that are supported on said lens substrate for
collimating incident light, a diffuse reflecting layer that is
formed over the lens substrate except in light entrance areas that
align with an optical axes of said lenses, and a shield layer that
is formed over the lens substrate on a side closer to the lenses
than said diffuse reflecting layer except in said light entrance
areas.
8. The liquid-crystal display apparatus according to claim 6,
wherein the pixel size of said liquid-crystal display panel is no
more than 200 .mu.m.
9. The liquid-crystal display apparatus according to claim 6,
wherein said collimated light has a divergence angle .theta. of no
more than .+-. 10.degree..
10. The liquid-crystal display apparatus according to claim 6,
wherein said liquid-crystal display panel is monochromatic.
11. A liquid-crystal display apparatus having a liquid-crystal
display panel, a backlight section that uses a collimating plate to
have collimated light launched into said liquid-crystal display
panel and a light diffusing plate that diffuses the image-bearing
light that has passed through said liquid-crystal display panel,
said apparatus satisfying the following relations: p/tan .theta.
.ltoreq. L d.times.tan .theta. .ltoreq. A where p is an average
pitch of emergence of said collimated light, .theta. is a
divergence angle of said collimated light, L is a distance from
said collimating plate to an interface in a liquid-crystal layer of
the liquid-crystal display panel which is directed to the
collimating plate, d is a distance from the light diffusing plate
to the interface in the liquid-crystal layer of said liquid-crystal
display panel which is directed to the light diffusing plate, and A
is a pixel size of said liquid-crystal display panel.
12. The liquid-crystal display apparatus according to claim 11,
wherein said backlight section has not only the collimating plate
but also a light source and a lamp housing for accommodating said
light source an inner surface of which is covered with a diffuse
reflecting layer, and said collimating plate has a lens substrate,
a multiple of lenses that are supported on said lens substrate for
collimating incident light, a diffuse reflecting layer that is
formed over the lens substrate except in light entrance areas that
align with an optical axes of said lenses, and a shield layer that
is formed over the lens substrate on a side closer to the lenses
than said diffuse reflecting layer except in said light entrance
areas.
13. The liquid-crystal display apparatus according to claim 11,
wherein the pixel size of said liquid-crystal display panel is no
more than 200 .mu.m.
14. The liquid-crystal display apparatus according to claim 11,
wherein said collimated light has a divergence angle .theta. of no
more than .+-. 10.degree..
15. The liquid-crystal display apparatus according to claim 11,
wherein said liquid-crystal display panel is monochromatic.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the technology of liquid-crystal
display apparatus, more particularly, to a liquid-crystal display
apparatus capable of producing high-contrast image over a wide
range of viewing angles.
[0002] The use of liquid-crystal displays (LCDs) as a display for
word processors and computers is rapidly increasing today. The use
of LCDs as a monitor in ultrasonic, CT and MRI diagnostic apparatus
is under review. Conventionally, these medical diagnostic apparatus
have primarily used CRTs (cathode-ray tubes) as a monitor.
[0003] LCDs have many advantages such as ease in size reduction,
small thickness and lightweightness. On the other hand, they have
poor viewing angle characteristics (narrow viewing angle) since as
the viewing direction or angle changes, the contrast of an image
decreases sharply and the gradation also reverses to have the image
look differently. As a result, depending on the position of the
viewer, the image cannot be viewed correctly.
[0004] In the medical applications described above, correct viewing
of images is important particularly for preventing wrong diagnosis.
What is more, diagnosis based on the difference in image density
requires that images of high contrast ratio be displayed over a
wide range of viewing angles. Another problem peculiar to medical
monitors is that image is usually displayed in monochrome (black
and white colors) and, hence, suffers considerable drop in contrast
as the viewing angle varies.
[0005] A known method for increasing the viewing angle of LCDs
relies upon using collimated backlight and the image-bearing light
that has passed through the liquid-crystal display panel is
diffused with a diffusing plate. This method increases the viewing
angle of the liquid-crystal display panel and enables the
fabrication of an LCD that produces high-contrast image display
over a wide range of viewing angles.
[0006] A problem with this method is that uneven display or blurred
image may occur if the collimated light and the liquid-crystal
display panel do not match in characteristics. For example, if the
average pitch of outgoing collimated light is larger than the pixel
size of the liquid-crystal display panel, the backlight is incident
in different quantities on the pixels of the liquid-crystal display
panel, producing unevenness in the image being displayed.
[0007] Since incorrect recognition of an image can cause wrong
diagnosis or inconsistency in the results of diagnosis, uneven
display and blurred image are particularly serious problems in the
medical applications.
SUMMARY OF THE INVENTION
[0008] The present invention has been accomplished under these
circumstances and has as an object providing a liquid-crystal
display apparatus that uses collimated backlight in combination
with a light diffusing plate in order to display high-contrast
image over a wide range of viewing angles and which yet can display
high-quality image without unevenness and blur that would otherwise
result from a mismatch between the characteristics of collimated
light and the liquid-crystal display panel adapted to have an
increased range of viewing angles.
[0009] In short, by using the liquid-crystal display apparatus of
the invention, high-quality images that are free from unevenness
and blurring can be displayed with high contrast over a wide range
of viewing angles.
[0010] In order to attain the object described above, the first
aspect of the present invention provides a liquid-crystal display
apparatus having a liquid-crystal display panel and a backlight
section that uses a collimating plate to have collimated light
launched into the liquid-crystal display panel, the apparatus
satisfying the following relation:
p/tan .theta. .ltoreq. L
[0011] where p is an average pitch of emergence of the collimated
light, .theta. is a divergence angle of the collimated light, and L
is a distance from the collimating plate to an interface in a
liquid-crystal layer of the liquid-crystal display panel which is
directed to the collimating plate.
[0012] The second aspect of the present invention provides a
liquid-crystal display apparatus having a liquid-crystal display
panel, a backlight section that uses a collimating plate to have
collimated light launched into the liquid-crystal display panel and
a light diffusing plate that diffuses the image-bearing light that
has passed through the liquid-crystal display panel, the apparatus
satisfying the following relation:
d.times.tan .theta..ltoreq. A
[0013] where .theta. is a divergence angle of the collimated light,
d is a distance from the light diffusing plate to an interface in a
liquid-crystal layer of the liquid-crystal display panel which is
directed to the light diffusing plate, and A is a pixel size of the
liquid-crystal display panel.
[0014] The third aspect of the present invention provides a
liquid-crystal display apparatus having a liquid-crystal display
panel, a backlight section that uses a collimating plate to have
collimated light launched into the liquid-crystal display panel and
a light diffusing plate that diffuses the image-bearing light that
has passed through the liquid-crystal display panel, the apparatus
satisfying the following relations:
p/tan .theta. .ltoreq. L
d.times.tan .theta. .ltoreq. A
[0015] where p is an average pitch of emergence of the collimated
light, .theta. is a divergence angle of the collimated light, L is
a distance from the collimating plate to an interface in a
liquid-crystal layer of the liquid-crystal display panel which is
directed to the collimating plate, d is a distance from the light
diffusing plate to the interface in the liquid-crystal layer of the
liquid-crystal display panel which is directed to the light
diffusing plate, and A is a pixel size of the liquid-crystal
display panel.
[0016] In the liquid-crystal display apparatus according to each
aspect of the present invention, it is preferable that the
backlight section has not only the collimating plate but also a
light source and a lamp housing for accommodating the light source
an inner surface of which is covered with a diffuse reflecting
layer, and the collimating plate has a lens substrate, a multiple
of lenses that are supported on the lens substrate for collimating
incident light, a diffuse reflecting layer that is formed over the
lens substrate except in light entrance areas that align with an
optical axes of the lenses, and a shield layer that is formed over
the lens substrate on a side closer to the lenses than the diffuse
reflecting layer except in the light entrance areas.
[0017] It is also preferable that the pixel size of the
liquid-crystal display panel is no more than 200 .mu.m.
[0018] It is another preferable that the collimated light has a
divergence angle .theta. of no more than .+-. 10.degree..
[0019] It is further preferable that the liquid-crystal display
panel is monochromatic.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows the liquid-crystal display apparatus of the
invention in conceptual form;
[0021] FIG. 2 shows in conceptual form the collimating plate used
in the liquid-crystal display apparatus of FIG. 1;
[0022] FIG. 3 shows in conceptual form the light diffusing plate
used in the liquid-crystal display apparatus of FIG. 1; and
[0023] FIGS. 4A and 4B are conceptual diagrams for illustrating the
liquid-crystal display apparatus of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] We now describe the liquid-crystal display apparatus of the
invention in detail with reference to the preferred embodiment
depicted in the attached drawings.
[0025] FIG. 1 shows an example of the liquid-crystal display
apparatus of the invention in conceptual form. The liquid-crystal
display apparatus generally indicated by 10 in FIG. 1 is a
so-called liquid-crystal display (hereunder referred to as LCD)
that utilizes a liquid-crystal display panel 12 as an image display
means. It is composed of the liquid-crystal display panel 12, a
light diffusing plate 16 that diffuses the image-bearing light that
has passed through the liquid-crystal display panel 12, and a
backlight section 14 that causes collimated light to be incident on
the liquid-crystal display panel 12.
[0026] In the illustrated case, the liquid-crystal display panel 12
is connected to its driver (not shown). The display apparatus 10 of
the invention is combined with any necessary members that are
included in known LCDs, such as a casing that has an image viewing
window and which holds the backlight section 14, liquid-crystal
display panel 12, light diffusing plate 16, the driver and other
members in position.
[0027] As in the conventional transmission LCD, the collimated
light issued from the backlight section 14 is launched into the
liquid-crystal display panel 12 being driven in accordance with the
image to be displayed and as it passes through the panel 12, the
collimated backlight bears the image and is diffused by the
diffusing plate 16 to produce image display.
[0028] In the display apparatus 10 of the invention, the
liquid-crystal display panel 12 (hereunder referred to simply as
the display panel 12) may be a known liquid-crystal display panel
used in various kinds of LCDs. In the illustrated case, the display
panel 12 has a liquid-crystal layer 20 sandwiched between two glass
substrates 18a and 18b, with a polarizer plate 22a (or 22b)
provided on the face of the glass substrate 18a (or 18b) away from
the liquid-crystal layer 20. Various kinds of optical compensating
filters (e.g. a phase compensating film) and the like may
optionally be provided between the glass substrate 18 and the
polarizer plate 22.
[0029] The display panel 12 may therefore be of a full-color or
monochromatic type and has no limitations on the type of liquid
crystal, liquid-crystal cell, drive means (switching device) such
as a TFF (thin-film transistor) and black matrix (BM).
[0030] The display panel 12 may be operated in all known modes
including a TN (twisted nematic) mode, an STN (supertwisted
nematic) mode, an ECB (electrically controlled birefringence) mode,
an IPS (in-plane switching) mode and an MVA (multi-domain vertical
alignment) mode.
[0031] In order that the display apparatus of the invention is also
suitable for use as a medical monitor, the pixel size of the
display panel 12 is preferably no more than 200 .mu.m, assuming
that one pixel in the invention is made up of R, G and B sub-pixels
if the apparatus is of a full-color type. Preferably, the display
panel 12 is monochromatic.
[0032] The backlight section 14 is a backlight for enabling the
viewing of the image being displayed by display panel 12. To issue
collimated light, the backlight section 14 comprises a housing 24,
light sources 26 and a collimating plate 28.
[0033] The housing 24 is a rectangular enclosure with one side open
and, in a preferred embodiment, its inner surfaces are covered with
a diffuse reflecting layer that reflects the incident light by
diffusion. This design allows for efficient use of the light from
the light sources 26 to produce intense collimated light. The
diffuse reflecting layer is not limited in any particular way and
any known type can be used as exemplified by one that is formed of
a dispersion of the fine particles of light diffusing materials
such as alumina (Al.sub.2O.sub.3) and titanium oxide
(TiO.sub.2).
[0034] The housing 24 has the light sources 26 in its interior. All
known types of light sources that are used in the so-called
transmission LCDs can be used as the light sources 26 as long as
they emit adequate quantities of light.
[0035] The collimating plate 28 condenses the light issued from the
light sources 26, as well as the light reflected by the inner
surfaces of the housing 24 and it emits collimated light. Having
this capability, the collimating plate 28 is placed to close the
opening of the housing 24.
[0036] The collimating plate to be used in the invention is not
limited in any particular way and various known types of
collimating plates may be used, as exemplified by a collimating
plate consisting of two crossed Fresnel lenses and a collimating
plate using a louver that transmits only part of scattered
light.
[0037] A preferred example of the collimating plate 28 is shown
schematically in FIG. 2. It comprises a lens substrate 30 in plate
form having a microlens array 32 (hereunder referred to as a lens
array 32) formed on one side as a two-dimensional arrangement of
hemispherical microlenses 32a. The side of the lens substrate 30
away from the lens array 32 is entirely covered with a light shield
layer 36 except in light entrance areas 34 that are set on-axis or
in alignment with the optical axes of the microlenses 32a. The side
of the lens substrate 30 which is closer to the incoming light than
the shield layer 36 (which in the illustrated case is on top of the
shield layer 36 with the lens substrate 30 taken as a base) is
entirely covered with a diffuse reflecting layer 38 except in the
light entrance areas 34.
[0038] As is clear from FIGS. 1 and 2, the collimating plate 28 is
fixed on the housing 24 with the lens array side facing the display
panel 12.
[0039] The light emerging from the housing 24 as indicated by the
one-long-one-short dashed lines in FIG. 2 is launched into the lens
substrate 30 via the light entrance areas 34, passes through it to
be launched into the microlenses 32a, refracted and emitted as
collimated light.
[0040] The light incident other than in the light entrance areas 34
is reflected by the diffuse reflecting layer 38 to go back into the
housing 24, where it is reflected to make another entry into the
collimating plate 28, thus increasing the efficiency of light
utilization. Any light passing through the diffuse reflecting layer
38 is blocked by the shield layer 36 and no stray light will occur
that can reduce the directivity of the collimated light.
[0041] The constituent materials of the lens substrate 30 and the
lens array 32 in the collimating plate 28 are not limited in any
particular way and various kinds of lens materials may be used as
exemplified by glass and various optical resins. The lens substrate
30 and the lens array 32 may be molded monolithically or they may
be separate members that are fixed in combination.
[0042] The microlenses 32a need not be hemispherical and they may
advantageously take on a shape produced by cutting an ellipsoid (of
revolution) through a plane perpendicular to its major axis.
[0043] The diffuse reflecting layer 38 and the shield layer 36 also
are not limited in any particular way and various known types may
be used. For example, the diffuse reflecting layer 38 may be made
of the same material as exemplified for the inner surfaces of the
housing 24 and the shield layer 36 may be made of chromium (Cr)
which is used in the BM of the display panel 12.
[0044] The methods of forming the diffuse reflecting layer 38 and
the shield layer 36 are not limited, either, and they may be formed
by any known methods such as thin-film forming techniques (e.g.
vapor deposition) and printing, the choice of which depends on
constituent materials and other factors.
[0045] Another preferred example of the collimating plate 28 is one
that replaces the hemispherical microlenses 32a with a number of
light-transmissive spherical beads that are fixed in one layer on a
transparent base sheet in such a way that they partly contact the
base sheet.
[0046] As is well known, collimators cannot convert diffuse light
into perfectly collimated light and the collimated light generally
has a certain degree of divergence. The collimating plate 28 used
in the display apparatus 10 of the invention is preferably of a
type that can emit collimated light having a divergence angle 0 of
no more than .+-.10.degree. and using this collimating plate, the
display apparatus 10 can provide a wider range of viewing
angles.
[0047] For the purposes of the present invention, the divergence
angle .theta. is defined by the half-peak width of the directional
characteristics of collimated light. More specifically, the
divergence angle .theta. is the angle the optical axis forms with
the position where the quantity of light from the optical axis is
halved.
[0048] As already mentioned, the collimated light issued from the
backlight section 14 is launched into the display panel 12 being
driven in accordance with the image to be displayed and as it
passes through the panel 12, the collimated backlight bears the
image and is diffused by the diffusing plate 16 to produce image
display to the viewer. It has also been mentioned that one can
increase the range of viewing angles of an LCD by using collimated
backlight and diffusing the image-bearing light from the display
panel 12 by means of the light diffusing plate 16.
[0049] The light diffusing plate 16 to be used in the display
apparatus 10 of the invention is not limited in particular way and
various known types of light diffusing plates (sheets) can be used,
as exemplified by a light diffusing plate having a transparent
electroconductive layer between a transparent base and a light
diffusing layer and which is disclosed in Unexamined Published
Japanese Patent Application (kokai) No. 333202/1993, and a light
diffusing plate in which a layer of crosslinked ion-conductive
resin having a cationic quaternary ammonium base at side chains is
provided between a transparent base and a light diffusing layer, as
disclosed in Unexamined Published Japanese Patent Application No.
5306/1995.
[0050] In a preferred embodiment, the illustrated display apparatus
10 uses a light diffusing plate 16 shown schematically in FIG. 3.
It comprises a lens substrate 40 in plate form having a microlens
array 42 (hereunder referred to as a lens array 42) formed on one
side as a two-dimensional arrangement of hemispherical microlenses
42a. The side of the lens substrate 40 away from the lens array 42
is entirely covered with a light shield layer 46 except in light
exit areas 44 that are set on-axis or in alignment with the optical
axes of the microlenses 42a. The side of the lens substrate 40
which is closer to the viewer's eyes than the shield layer 46 is
entirely covered with an anti-reflection (AR) layer 48 except in
the light exit areas 44.
[0051] As is clear from FIGS. 2 and 3, the light diffusing plate 16
has basically the same construction as the aforementioned
collimating plate 28 except that the diffuse reflecting layer 36 is
replaced by the anti-reflection layer 48.
[0052] The light diffusing plate 16 is fixed on the housing with
the lens array side facing the display panel 12. The light
diffusing plate 16 works in a way just opposite to the
aforementioned collimating plate 12; the image-bearing collimated
light emerging from the display panel 12 is launched into the
microlenses 42a, where it is diffused by refraction and thence
issued from the light exit areas 44 as diffused light. Any stray
light that is incident other than in the light exit areas 44 is
blocked by the shield layer 46 and there will be no interference
with image viewing.
[0053] FIG. 3 shows a preferred case where the anti-reflection
layer 48 is formed on the viewing side of the light diffusing plate
16 and this ensures the viewing of satisfactory image. The
anti-reflection layer 48 is not limited in any particular way and
various known types of anti-reflection layer can be used.
[0054] Various parameters of the display apparatus 10 of the
invention are shown schematically in FIGS. 4A and 4B. If the
average pitch of emergence of collimated light from the collimating
plate 12 (which in the illustrated case is the distance between the
optical axes of adjacent microlenses 32a) is written as p, the
divergence angle of the collimated light as .theta., the distance
from the collimating plate 12 (the surface of the microlens array
32) to the interface in the liquid-crystal layer 20 which is
directed to the collimating plate 12 (i.e., the interface with the
glass substrate 18a) as L, the distance from the light diffusing
plate 16 (the surface of the microlens array 32) to the interface
in the liquid-crystal layer 20 which is directed to the light
diffusing plate 16 (i.e., the interface with the glass substrate
18b) as d, and the pixel size of the display panel 12 as A, the
collimated light, collimating plate 28 and display panel 12 satisfy
the relation p/tan .theta. .ltoreq. L and the collimated light,
display panel 12 and light diffusing plate 16 satisfy the relation
d.times.tan .theta..ltoreq. A.
[0055] As mentioned earlier, no collimators can produce perfectly
parallel light and any collimated light has a certain divergence
angle .theta. that varies with the performance of the collimator;
in other words, its quantity is distributed from the optical axis
outward.
[0056] In the conventional LCD using collimated backlight, the
liquid-crystal layer 20 is typically located in the position
indicated by the dashed line in FIG. 4A. As a result, the image
being displayed is adversely affected by the distribution
(unevenness) in the quantity of collimated light and uneven display
occurs. Particularly in the case where the pitch p of the
collimated light is greater than the pixel size A of the display
panel, the unevenness in the quantity of collimated light appears
directly in the displayed image to produce an uneven display.
[0057] According to the study of the present inventors, if the
liquid-crystal layer 20 is located in such a position that
neighboring beams of the incident collimated light overlap each
other by an amount at least equal to one half the pitch p (see FIG.
4A), the collimated light incident on the liquid-crystal layer 20
is averaged to eliminate any unevenness in quantity and, hence, the
resulting unevenness in display is prevented to ensure the display
of a high-quality image.
[0058] In the present invention, the collimated light, collimating
plate 28 and display panel 12 (liquid-crystal layer 20) satisfy the
relation p/tan .theta. .ltoreq. L and given this design, adjacent
beams of the collimated light incident on the liquid-crystal layer
20 overlap each other by an amount at least equal to one half the
pitch p and, as a result, a high-quality image can be displayed
without any unevenness.
[0059] In an exemplary case, if the collimated light has a
divergence angle .theta. of 10.degree. and the pitch p between
adjacent emerging beams is 600 .mu.m, the distance L may be
adjusted to 3.4 mm or more.
[0060] In its preferred embodiment, the invention also satisfies
the relation p/tan .theta. .ltoreq. Lf, where Lf is the distance
between the collimating plate 28 and the outermost surface of the
display panel 12 which faces the collimating plate 28 (which in the
illustrated case is the side of the polarizer plate 22a which faces
the collimating plate 28). If this condition is met, the collimated
light entering the polarizer plate 22a and any optical compensating
film that is optionally inserted in the display panel 12 is also
averaged to eliminate any unevenness in the quantity of the
collimated light and, as a result, uneven display is prevented in a
more efficient and positive way to enable the display of an image
of even higher quality.
[0061] The collimated light emerging from the collimating plate 28
continues to travel with the same divergence angle of .theta. as it
passes through the display panel 12. The glass substrate 18b and
the polarizer plate 22b are provided between the liquid-crystal
layer 20 and the light diffusing plate 16; in addition, an optical
compensating film such as a phase compensating film may optionally
be inserted. Hence, with the conventional LCD, beams of the
collimated light that bear images of different pixels overlap each
other when they enter the light diffusing plate 16 and diffusion
subsequently takes place. As a result, a blurred image will form in
the conventional LCD which uses collimated backlight.
[0062] According to the study of the present inventors, if beams of
the collimated light that bear images of neighboring pixels do not
overlap by an amount exceeding one half the pixel size A (see FIG.
4B), the deterioration in image quality due to blurring can be
substantially reduced.
[0063] In the present invention, the collimated light, display
panel 12 and light diffusing plate 16 satisfy the relation
d.times.tan .theta..ltoreq. A and given this design, a high-quality
image can be displayed without any blur.
[0064] Take, for example, the case where the glass substrate 18b is
0.7 mm thick and the polarizer plate 22b is 0.2 mm thick. Since the
distance d from the liquid-crystal layer 20 to the light diffusing
plate 16 is 0.9 mm, a blur-free high-quality image can be produced
by adjusting the pixel size A of the display panel 12 to at least
159 .mu.m on the condition that the collimated light has a
divergence angle .theta. of 10.degree..
[0065] If an optical compensating film 0.2 mm thick is additionally
inserted between the polarizer plate 22b and the light diffusing
plate 16 (to increase the distance d to 1.1 mm), the pixel size A
of the display panel 12 need be at least 194 .mu.m.
[0066] Thus, the display apparatus 10 of the invention effectively
combines collimated backlight with the light diffusing plate to
increase the range of viewing angles while preventing any
unevenness in image display and blurred images that would otherwise
occur on account of the effort to increase the range of viewing
angles. Hence, the display apparatus of the invention can
advantageously be used as a medical monitor which is required to
display images of high contrast and quality over an increased range
of viewing angles.
[0067] In the embodiment described above, the collimated light,
collimating plate 28 and the liquid-crystal panel 12 satisfy the
relation p/tan .theta. .ltoreq. L and the collimated light, display
panel 12 and the light diffusing plate 16 satisfy the relation
d.times.tan .theta..ltoreq. A. This is not the sole case of the
invention and it suffices for the purpose of the invention if
either one of those relations is satisfied. In these alternative
embodiments, too, one can produce high-quality images that are
substantially reduced in unevenness and blur compared to the
conventional LCD which combines collimated backlight with the light
diffusing plate to increase the range of viewing angles.
[0068] While the liquid-crystal display apparatus of the invention
has been described above in detail with reference to various
embodiments, it should be understood that the invention is by no
means limited to the foregoing embodiments alone and various
improvements and design modifications may of course be made without
departing from the scope and spirit of the invention.
[0069] As will be understood from the foregoing description, the
liquid-crystal display apparatus of the invention effectively
combines collimated backlight with the light diffusing plate to
display high-contrast images over a wide range of viewing angles
and the displayed images have high quality while effectively
reducing any unevenness and blur that would otherwise result from
the effort to increase the range of viewing angles.
[0070] Consequently, the liquid-crystal display apparatus of the
invention is particularly suitable for use as a medical monitor
that is required to display high-quality images over a wide range
of viewing angles.
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