Illumination – Revolving
Reexamination Certificate
2002-04-24
2004-09-28
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S027000, C362S559000, C362S560000, C362S026000
Reexamination Certificate
active
06796669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a light guide plate, an illuminating device and a display device having the same. More particularly, the present invention relates to a light guide plate preferably used as a frontlight of a reflection-type liquid crystal display device (LCD), an illuminating device and a display device having the same.
2. Description of the Background Art
Liquid crystal display devices (LCDs) are thin, low power consumption display devices. Because of such characteristics, the LCDs are recently used in a variety of applications including office automation (OA) equipments such as word processors and personal computers, portable information equipments such as electronic organizers, and camera-incorporated VTRs (video tape recorders) having a liquid crystal monitor.
These LCDs are roughly divided into two types: reflection type and transmission-type. An LCD is not a self-light-emitting display device such as CRT (cathode ray tube) and EL (electroluminescence). For display, a transmission-type LCD uses light of an illuminating device provided behind a liquid crystal display (LCD) panel (so-called backlight), whereas a reflection-type LCD uses ambient light.
Some known reflection-type LCDs have an illuminating device for improving display quality when ambient light having a sufficient intensity is not available. This illuminating device is called “frontlight”, while the illuminating device of the transmission-type LCDs is called “backlight”.
Various illuminating devices are conventionally proposed as such a backlight and frontlight. For example, Japanese Laid-Open Publication No. 8-94844 discloses an illuminating device
400
used as a backlight and frontlight, as schematically shown in FIG.
38
. Hereinafter, the structure of a reflection-type LCD
450
having the illuminating device
400
as a frontlight will be described with reference to FIG.
38
.
The reflection-type LCD
450
has a reflection-type LCD panel
430
and an illuminating device (frontlight)
400
provided on the viewer side of the reflection-type LCD panel
430
. The illuminating device
400
has a light source
410
and a light guide plate
420
. A reflecting member
412
surrounds the light source
410
.
The light guide plate
420
has a first side surface (incident side surface)
422
a
located at the light source
410
, a second side surface (opposing side surface)
422
b
facing the first side surface
422
a,
third and fourth side surfaces (not shown), an emitting surface
422
c
for emitting the incident light from the light source
410
, and an opposing surface
422
d
facing the emitting surface
422
c.
The third and fourth side surfaces are located between the first side surface
422
a
and the second side surface
422
b
so as to face each other. The reflection-type LCD panel
430
is mounted so as to face the emitting surface
422
c
of the light guide plate
420
. The opposing surface
422
d
has propagating surfaces
422
d
1
and reflecting surfaces
422
d
2
, and has a saw-tooth cross-section.
Light emitted from the light source
410
into the light guide plate
420
through the first side surface
422
a
is propagated toward the second side surface
422
b
while being repeatedly totally reflected by the propagating surfaces
422
d
1
and the emitting surface
422
c.
The light propagated through the light guide plate
420
is partially reflected by the reflecting surfaces
422
d
2
and emitted from the emitting surface
422
c
toward the reflection-type LCD panel
430
. The light reflected by the reflection-type LCD panel
430
is directed back into the light guide plate
420
through the emitting surface
422
c.
After passing through the light guide plate
420
, the reflected light is emitted from the opposing surface
422
d
toward the viewer for use in display.
Japanese Laid-Open Publication No. 10-268307 discloses an illuminating device
500
used as a frontlight, as schematically shown in FIG.
39
A. Hereinafter, the structure of a reflection-type LCD
550
having the illuminating device
500
as a frontlight will be described with reference to FIG.
39
A.
The reflection-type LCD
550
has a reflection-type LCD panel
530
and an illuminating device (frontlight)
500
provided on the viewer side of the reflection-type LCD panel
530
. The illuminating device
500
has a light source
510
and a light guide plate
520
. A reflecting member
512
surrounds the light source
510
. A condenser
513
is provided between the light source
510
and the light guide plate
520
.
The light guide plate
520
has an incident side surface
520
a
located at the light source
510
, an emitting surface
520
b
facing the reflection-type LCD panel
530
, an opposing surface
520
c
located on the viewer side and facing the emitting surface
520
b,
and first and second side surfaces (not shown). The first and second side surfaces face each other with the incident side surface, emitting surface and opposing surface interposed therebetween. The light guide plate
520
has a wedge-like shape so that the distance between the emitting surface
520
b
and the opposing surface
520
c
is reduced as the distance from the incident side surface
520
a
is increased. The light guide plate
520
has a triangular cross section along the direction perpendicular to the emitting surface
520
b
and the opposing surface
520
c.
The incident side surface
520
a
is tilted with respect to the normal to the emitting surface
520
b,
and forms an obtuse angle with the emitting surface
520
b.
Light emitted from the light source
510
into the light guide plate
520
through the incident side surface
520
a
is propagated within the light guide plate
520
. Of the light propagated within the light guide plate
520
, the light that does not satisfy the conditions for total reflection at the emitting surface
520
a
is emitted from the emitting surface
520
b
toward the reflection-type LCD panel
530
. The light reflected by the reflection-type LCD panel
530
is directed back into the light guide plate
520
through the emitting surface
520
b.
After passing through the light guide plate
520
, the reflected light is emitted from the opposing surface
520
c
toward the viewer for use in display.
Japanese Laid-Open Publication No. 10-268307 discloses a reflection-type LCD
550
′ having an illuminating device
500
′ used as a frontlight, as schematically shown in FIG.
39
B. The reflection-type LCD
550
′ is different from the reflection-type LCD
550
in that the reflection-type LCD
550
′ has a light traveling direction controller
524
. In the reflection-type LCD
550
′, the light traveling direction controller
524
is provided so as to face the emitting surface
520
b
of the light guide plate
520
. Therefore, as the light emitted from the emitting surface
520
b
passes through the light traveling direction controller
524
, the traveling direction thereof is changed toward the direction normal to the emitting surface
520
b.
However, the inventor found that the illuminating devices disclosed in the above publications have the following problems:
In the illuminating device
400
disclosed in the aforementioned Japanese Laid-Open Publication No. 8-94844, the propagating surfaces
422
d
1
and the reflecting surfaces
422
d
2
form concaves and convexes at the opposing surface
422
d
of the light guide plate
420
. Therefore, any damage to such concaves and convexes or adhesion of foreign matters thereto would adversely affect the illumination light, degrading display quality of the LCD. When the illuminating device
400
is used as a frontlight, the opposing surface
422
d
is located on the viewer side. Therefore, such problems are especially likely to occur, and the reflection-type LCD
450
having the illuminating device
400
as a frontlight as shown in
FIG. 38
would be subjected to significant degradation in display quality.
In order to prevent such damages to the concaves and convexes and adhesion of f
Husar Stephen
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Zeade Bertrand
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