Illumination – Revolving
Reexamination Certificate
2002-10-22
2004-10-12
Ward, John Anthony (Department: 2875)
Illumination
Revolving
C362S026000, C362S330000
Reexamination Certificate
active
06802619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface-emitting device and a liquid crystal display device, and more particularly, to the configuration of a surface-emitting device that serves to utilize, as illumination light, more of the light emitted from a light source.
2. Description of the Related Art
Hitherto, in reflective liquid crystal display devices that produce display with ambient light used as a light source, the visibility of the display extremely decreases in an environment in which sufficient ambient light cannot be obtained, for example, when used in a dark place, because the luminance depends on the amount of ambient light. Accordingly, a liquid crystal display device has been proposed in which a front light (surface-emitting device) is placed in front of a reflective liquid crystal display unit (liquid crystal display element) so that it is used as an auxiliary light source. The liquid crystal display device having the front light operates as a normal reflective liquid crystal display device in an environment in which sufficient ambient light can be obtained, for example, outdoors in the daytime, and illuminates the front light as the light source, as necessary. An example of the configuration of such a front light will be described below with reference to
FIGS. 11
to
13
.
A front light
110
shown in
FIG. 11
includes a flat light guide panel
112
formed by injection-molding a transparent acrylic resin or the like, and a plurality of (two in the figure) light sources
111
disposed at an end face
112
a
of the light guide panel
112
. The lower surface of the light guide panel
112
in the figure serves as an emergent surface from which light for illuminating a liquid crystal display unit is emitted, and a surface (the upper surface of the light guide panel
112
) on the opposite side of the emergent surface serves as a prism surface
112
c
on which projections
114
shaped like a wedge in profile are continuously arranged in parallel so as to change the direction of light propagating inside the light guide panel
112
. The light sources
111
are point light sources such as white LEDs (Light Emitting Diodes) or organic EL (Electro Luminescence) elements, and are arranged so as to emit light toward the end face
112
a
of the light guide panel
112
.
In the front light
110
having the above configuration shown in
FIG. 11
, light emitted from the light sources
111
is introduced into the light guide panel
112
through the end face
112
a
, and the light propagating therein is reflected by the prism surface
112
c
so as to change the propagating direction, and is emitted from the emergent surface (lower surface) of the light guide panel
112
. The emitted light illuminates a liquid crystal display unit or the like placed on the back side of the front light
110
.
However, since the front light
110
has a structure in which the point light sources
111
are placed at the end face
112
a
of the light guide panel
112
, the intensity of the light introduced into the light guide panel
112
is inevitably nonuniform, and as a result, light emitted from the emergent surface is also nonuniform. Accordingly, in order to increase the uniformity of the emitted light, a front light
120
is in practical use in which a light guide bar
113
is provided between a light guide panel
112
and light sources
115
, as shown in FIG.
12
.
In this front light
120
, as shown in
FIG. 12
, the light guide bar
113
is placed along an end face of the light guide panel
112
, and the light sources
115
formed of an LED serving as a light-emitting element are placed at both ends in the longitudinal direction of the light guide bar
113
. An outer side face (a side face on the opposite side of the light guide panel
112
)
113
a
of the light guide bar
113
has a prismatic shape (not shown) that can reflect light propagating inside the light guide bar
113
so as to change the propagating direction.
Therefore, in the front light
120
, light emitted from the light sources
115
is introduced into the light guide bar
113
through both end faces thereof, is caused by the prism surface formed on the outer side face
113
a
of the light guide bar
113
to change the propagating direction, and is introduced into the light guide panel
112
from the end face.
Since the front light
120
has the light guide bar
113
in this way, light is introduced from the entire connecting surface between the light guide panel
112
and the light guide bar
113
into the light guide panel
112
, and this improves the uniformity of the light emitted from the emergent surface of the light guide panel
112
.
While the distribution of emergent light is relatively uniform in the front light
120
having the above configuration, the luminance necessary to illuminate the liquid crystal display unit is insufficient. Furthermore, light introduced into the light guide panel
112
directly reaches the viewer from the surface (upper surface) of the light guide panel
112
, and this causes a phenomenon in which the surface of the light guide panel
112
looks white (whitening), and reduces visibility. In order to solve this problem, a front light having a configuration shown in
FIG. 13
has been suggested. In this front light
130
, a metal cover member
118
having an angular-U profile is mounted from the side of the light guide bar
113
of the front light
130
shown in FIG.
12
. This cover member
118
includes a reflecting-surface covering portion
118
a
placed at a reflecting surface
112
c
of the light guide panel
112
, a light-guide covering portion
118
c
placed outside the light guide bar
113
, and an emergent-surface covering portion
118
b
placed at an emergent surface (lower surface) of the light guide panel
112
. These covering portions prevent light propagating inside the light guide bar
113
and the light guide panel
112
from being emitted in the directions other than the light guide direction (the direction from the light guide bar
113
toward the light guide panel
112
).
In the front light
130
having such a configuration, since a decrease in luminance caused by the light loss due to the light leakage in the directions other than the light guide direction can be reduced, illumination with higher luminance than in the front light
120
shown in
FIG. 12
is possible. However, since the display quality has recently been improved for higher-definition and higher-contrast liquid crystal display devices, the front lights have been required to further enhance the luminance and to further improve the uniformity of emergent light, and the development of front lights that achieve a higher-luminance and more uniform illumination has been demanded.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a surface-emitting device that achieves high utilization efficiency of a light source, high luminance, and high uniformity of emergent light.
Another object of the present invention is to provide a liquid crystal display device having a surface-emitting device that has the above superior characteristics and achieves high visibility.
In order to achieve the above objects, according to one aspect, the present invention provides a surface-emitting device including a light guide panel, a light guide placed along an end face of the light guide panel, and light sources placed at opposing ends of the light guide, wherein a reflecting surface of the light guide panel has irregularities for reflecting light propagating therein, an emergent surface of the light guide panel emits light reflected by the reflecting surface, a cover member including at least a reflecting-surface covering portion that covers an end of the light guide panel on the side of the reflecting surface, a light-guide covering portion that covers the light guide, and an emergent-surface covering portion that covers an end of the light guide panel on the side of the emergent surface is mounted so as to cover at least the light guide and the ends
Ohizumi Mitsuo
Sugiura Takuro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ward John Anthony
LandOfFree
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