Illumination – Revolving
Reexamination Certificate
2001-12-11
2003-11-25
Cariaso, Alan (Department: 2875)
Illumination
Revolving
C362S561000, C349S063000
Reexamination Certificate
active
06652109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface light emission device, a method of manufacturing the same, and a liquid crystal display device, and more specifically, to the structure of a surface light emission device that is preferably used as a front light of a liquid crystal display device.
2. Description of the Related Art
Reflection type liquid crystal display devices that display an image using sun light and illuminating light as a light source are used in mobile phones and mobile information terminals because their power consumption is small. However, the reflection type liquid crystal display device has a problem that it is very poor at a display capability in a dark place where external light is not available. To solve this problem, there are known semi-transmission/reflection type liquid crystal display devices which are arranged such that a back light is disposed to the reflection type liquid crystal display devices so that an image can be displayed in a light transmission mode by tuning on the back light at a location where external light is not available.
However, it is very difficult for the semi-transmission/reflection type liquid crystal display device to make the brightness of display in a semi-transmission mode compatible with the brightness of display in a reflection mode because it is necessary to pass the light from the back light through a reflection film composed of a metal thin film.
To cope with this problem, there have been developed liquid crystal display devices provided with a surface light emission device (front light). In this liquid crystal display device, light from a light source such as a cold-cathode tube which is introduced from a side end surface of a light introduction plate is caused to outgo from a surface thereof and illuminates the liquid crystal display device from the front surface thereof. The provision of the surface light emission device in front of the front surface of the liquid crystal display device permits an image to be displayed in a reflection mode even in a dark place similarly to a case in which external light is used.
FIG. 15
is a structural view in cross section showing an example of a liquid crystal display device having a front light in front of a liquid crystal display unit. In the figure, the liquid crystal display device
100
comprises the front light
110
and the liquid crystal display unit
120
. The front light
110
comprises a light introduction plate
112
which is composed of a transparent acrylic resin and a light source
113
which is composed of a cold-cathode tube or a LED (light emitting diode) and disposed to a side end surface
112
a
of the light introduction plate
112
. A plurality of grooves
114
are continuously formed in a stripe shape on the opposing surface
112
c
of the light introduction plate
112
which is opposite to the light outgoing surface
112
b
thereof. Each of the grooves
114
is composed of two slanting surfaces which are formed to slant with respect to the light outgoing surface
112
b.
The two slanting surfaces are composed of a gentle slanting surface
114
a
and a steep slanting surface
114
b
which has a slanting angle steeper than that of the gentle slanting surface
114
a
, and the gentle and steep slanting surfaces
114
a
and
114
b
are alternately and continuously formed on the opposing surface
112
c
of the light introduction plate
112
.
The liquid crystal display unit
120
is arranged such that a pair of glass substrates
121
and
122
, which are opposite to each other through a liquid crystal layer
123
sandwiched therebetween, are joined together through a seal member
124
. In the liquid crystal display unit
120
, a reflection film
125
and a display circuit
126
are formed so as to be sandwiched between the glass substrate
121
and the liquid crystal layer
123
. A display circuit
127
is formed so as to be sandwiched between the glass substrate
122
and the liquid crystal layer
123
. Although not shown, the display circuits
126
and
127
include circuits for driving and controlling the liquid crystal layer
123
such as an electrode layer and an orientation film.
In the liquid crystal display device
100
, the light introduction plate
112
of the front light
110
is disposed in front of the front surface (upper surface in the figure) of the display region of the liquid crystal display unit
120
. The light emitted from the light source
113
is introduced to the light introduction plate
112
through the side end surface
112
a
thereof, is reflected by the light outgoing surface
112
b
and the opposing surface
112
c
, and travels through the inside of the light introduction plate
112
. At the same time, the light is reflected by the steep slanting surface
114
b
, which has the steeper slanting angle, of two slanting surfaces
114
a
and
114
b
formed on the opposing surface
112
c
, and thereby the direction of the light is changed in a direction where the light travels to the light outgoing surface
112
b
and the light outgoes from the light outgoing surface
112
b
. The front light
110
illuminates the liquid crystal display unit
120
by the arrangement as described above. Next, the light incident on the liquid crystal display unit
120
passes through the respective display circuits
126
and
127
and the liquid crystal layer
123
, reaches the reflection film
125
and is reflected thereby, and returns to the outside of the liquid crystal display unit
120
again. The reflected light passes through the front light
110
and reaches a viewer, and an image displayed on the liquid crystal display unit
120
is visually confirmed by the viewer.
According to the liquid crystal display device
100
arranged as described above, it is possible to display an image even in a dark place by turning on the front light
110
, and the image can be displayed brightly at a portion near to the light source
113
. However, the image is made darker at a portion thereof which is located farther from the light source
113
. In a usual front light, the brightness of the portion of an image displayed at a position about 50 mm apart from the light source
113
is only about one-half that of the portion of the image displayed in the vicinity of the light source
113
. Accordingly, it is only a part of the display region of the liquid crystal display device
100
that can realize a sufficient visual property in a dark place. Further, there is also a problem that the existence of the region where an image is displayed dark makes it all the more difficult to view the displayed image.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention, which was made to solve the above problem, to provide a surface light emission device capable of obtaining a sufficient quantity of light even at a place apart from a light source, a method of manufacturing the same, and a liquid crystal display device capable of displaying an image the brightness of which is uniform over an entire display region.
In the present invention, a means for solving the above problems is arranged as a surface light emitting device which includes a light source and a light introduction plate having a structure for causing the light from the light source to be incident from a side end surface and causing the light to outgo from a light outgoing surface, wherein a plurality of grooves each composed of a gentle slanting surface and a steep slanting surface having a slanting angle steeper than that of the gentle surface are periodically formed in a stripe shape on the opposing surface of the light introduction plate opposite to the light outgoing surface, and a groove having a larger distance from the light source of the grooves is formed deeper as well as the difference between the depths of adjacent grooves is made larger as they have a distance longer from the light source.
In the surface light emitting device of the present invention, it is preferable that the depth H
n+1
of a (n+1)-th groove from the light
Alps Electric Co. ,Ltd.
Cariaso Alan
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