Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2002-07-23
2004-10-19
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S063000, C349S065000, C349S113000, C362S035000
Reexamination Certificate
active
06806922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface light-emitting device and a liquid crystal display device.
2. Description of the Related Art
Hitherto, in reflective liquid crystal display devices using ambient light as a light source, the brightness depends on the amount of ambient light, and thus the display visibility significantly deteriorates in circumstances where a sufficient amount of ambient light cannot be obtained, such as in dark places.
In order to overcome this problem, a liquid crystal display device in which a front light (surface light-emitting device), functioning as an auxiliary light source, is provided on the front surface of a reflective liquid crystal display unit has been proposed. This type of liquid crystal display device including the front light operates as an ordinary reflective liquid crystal display device in circumstances where sufficient ambient light can be obtained, such as outdoors during daytime. Also, the front light can be used as a light source as required.
FIG. 12
is a sectional view showing an example of a liquid crystal display device provided with a front light on the front surface of a liquid crystal display unit. The liquid crystal display device
200
shown in
FIG. 12
includes a liquid crystal display unit
220
and a front light
210
. The front light
210
is placed on the front surface (upper surface in
FIG. 12
) of the liquid crystal display unit
220
so that a light guide panel
212
is placed in the display area of the liquid crystal display unit
220
.
The front light
210
includes the light guide panel
212
, which is made by injection molding of a transparent acrylic resin or the like, and a light source
213
comprising a cold-cathode tube or the like provided on an end surface
212
a
of the light guide panel
212
. The lower surface (the liquid crystal display unit
220
side) of the light guide panel
212
is an exit surface
212
b
from which light is emitted. The surface facing the exit surface
212
b
(the upper surface of the light guide panel
212
) is a reflecting surface
212
c
provided with a first slope
214
a
formed to incline with respect to the exit surface
212
b
so as to change the direction of light inside the light guide panel
212
and a second slope
214
b
which is continuous with the first slope
214
a
, the first and second slopes
214
a
and
214
b
being repeatedly placed one after another.
The liquid crystal display unit
220
includes a first substrate
221
and a second substrate
222
, which face each other with a liquid crystal layer
223
therebetween, and a sealing material
224
for joining the first substrate
221
and the second substrate
222
. On the liquid crystal layer
223
side of the first substrate
221
, a reflecting layer
230
including an organic film
228
and a reflecting film
225
, which is formed on the organic film
228
and which reflects incoming light, and a display circuit
226
for driving and controlling the liquid crystal layer
223
are laminated in this order. Also, a display circuit
227
is formed on the liquid crystal layer
223
side of the second substrate
222
. As shown in
FIG. 12
, the upper surface (the surface on the liquid crystal layer
223
side) of the organic film
228
is uneven so that the light reflected by the reflecting film
225
formed on the surface of the organic film
228
is diffused.
In the liquid crystal display device
200
having the above-described configuration, light from the light source
213
enters the light guide panel
212
via the end surface
212
a
of the light guide panel
212
, passes through the light guide panel
212
, is reflected at the first slope
214
a
having the larger slope angle with respect to the light guide direction, the direction of the light is changed toward the exit surface
212
b
, and the light is radiated from the exit surface
212
b
. The light from the exit surface
212
b
enters the liquid crystal display unit
220
as illuminating light, passes through the display circuits
226
and
227
and the liquid crystal layer
223
, is reflected by the reflecting film
225
, returns to the outside of the liquid crystal display unit
220
, passes through the exit surface
212
b
and the reflecting surface
212
c
of the light guide panel
212
, and reaches the user. In this way, the display of the liquid crystal display unit
220
is seen by the user.
The liquid crystal display device
200
having the above-described configuration can be used even in dark places, where ambient light cannot be used, by turning on the front light
210
as required. However, when display brightness using ambient light as a light source is compared to the display brightness using the front light
210
, the display brightness using the front light
210
is lower. Accordingly, when display is performed by switching on/off the front light, the display is difficult to see due to the difference in brightness, and therefore the device is not user-friendly.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a surface light-emitting device which has a high luminance and a good brightness distribution in the display, and which is preferably provided on the front surface of a reflective liquid crystal display unit.
Also, it is another object of the present invention to provide a liquid crystal display device having a surface light-emitting device in which a bright display can be realized when the surface light-emitting device is either on or off and an excellent visibility can be realized.
The above-described reflective liquid crystal display device
200
including the front light
210
is used for a display unit of mobile phones and mobile information terminals. The liquid crystal display device incorporated into such electronic equipment is often used so that the direction of an external light source and the direction of the line of sight of a user receiving the reflection light from the liquid crystal display device
200
are in a specific range. This will be described below with reference to
FIGS. 12 and 13
.
FIG. 13
is a side view showing an example of a mobile phone including the above-described liquid crystal display device
200
as a display unit. The mobile phone
250
shown in this figure includes an operation unit
260
and a display unit
270
. The operation unit
260
and the display unit
270
are coupled to each other by a hinge
280
provided therebetween and the display unit
270
can be opened and closed with respect to the operation unit
260
, with the hinge
280
being a supporting point. A plurality of operation buttons
261
are provided on the inner side of the operation unit
260
and the liquid crystal display device
200
is provided on the inner side of the display unit
270
. When used, the display unit
270
is opened, with the hinge
280
acting as a supporting point, as shown in
FIG. 13
, so that the liquid crystal display device
200
provided on the inner side of the display unit
270
can be seen by the user.
The liquid crystal display device
200
provided in the mobile phone
250
shown in
FIG. 13
performs display by allowing the reflecting layer
230
of the liquid crystal display unit
220
to reflect incoming light Q entering at a predetermined angle with respect to the normal line P of the liquid crystal display device
200
, when the external light is used as a light source. At that time, the user U is often located a little away from the normal line P of the liquid crystal display device
200
(the operation unit
260
side) as shown in FIG.
13
. Accordingly, the inventors of the present invention have found that the direction of reflection light Q′ generated by specularly reflecting the incoming light Q should substantially correspond with the direction of the line of sight of the user U in order to make the display brighter in the direction of the line of sight of the user U.
The inventors have studied the luminan
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Chowdhury Tarifur R.
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