Illumination – Revolving
Reexamination Certificate
2001-10-24
2004-03-30
Cariaso, Alan (Department: 2875)
Illumination
Revolving
C362S561000, C349S064000, C349S065000
Reexamination Certificate
active
06712482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an illumination device including a light guide which receives light emitted by a light source at a light-receiving face of the light guide, guides the light to a light-emitting face of the light guide, and emits the light to the outside. The present invention also relates to a liquid crystal apparatus using the illumination device.
2. Description of the Related Art
Liquid crystal apparatuses are widely known as electro-optical displays. Generally, in the liquid crystal apparatus, liquid crystal is sandwiched between a pair of substrates each provided with electrodes, and the orientation of the liquid crystal is controlled by applying a voltage between the electrodes, thereby modulating light transmitted through the liquid crystal and displaying images.
When classifying the liquid crystal apparatuses according to the method of supplying light to the liquid crystal, various liquid crystal apparatuses are known, such as a reflective-type liquid crystal apparatus in which external light is reflected by a reflector provided on the outer or inner face of one of the pair of substrates, a transmission-type liquid crystal apparatus in which a planar light is applied to the liquid crystal by an illumination device provided on the outer face of one of the pair of substrates, and a semi-transmission reflective liquid crystal apparatus (i.e., transflective) which functions as a reflective-type liquid crystal apparatus when there is sufficient external light and as a transmission-type liquid crystal apparatus when not enough external light is applied.
The illumination device which is used in a transmission-type liquid crystal apparatus or semi-transmission reflective liquid crystal apparatus, as shown in
FIG. 8
, basically has a light source
71
, such as an LED (light emitting diode) or a cold cathode tube, opposing a light-receiving face
74
a
of a light guide
74
, introduces the light received by the light-receiving face
74
a
from the light source
71
into the light guide
74
, guides the light while the light is reflected by a reflector
74
b
to a light-emitting face
74
b
, and emits the light to the outside from the light-emitting face
74
b
. A device, for example, a liquid crystal panel (not shown) which uses a planar light is disposed at the light-emitting face
74
b
, and the planar light is supplied to the device. Note that a reference symbol R shows conceptual light paths, and it does not show actual light paths.
Recently, color displays using liquid crystal apparatuses have become popular. In order to perform attractive display by using color displays, it is necessary that the light for illuminating the liquid crystal panel has high luminance. In particular, a luminance of app approximately 2 cd/m
2
is required for a monochrome display. On the other hand, a high luminance of 10 cd/m
2
or more is required for a color display. Moreover, a color display panel has a low light-transmissivity which is, for example, of the order of 2%. Therefore, the illumination device is required to generate high-luminance light.
Although, as described above, the illumination devices have been recently required to generate high-luminance emission light, the light introduced into the light guide
74
is inefficiently emitted to the outside from the light-emitting face
74
b
in the known basic illumination device shown in FIG.
8
. Therefore, there has been a problem that emitted light having high luminance cannot be obtained.
A known illumination device is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 6-082631, in which unevenness in light generation in the vicinity of the edges of the illumination device is avoided with a diffusion member or a light-absorbing member disposed at an end face of a light guide. A known illumination device is also disclosed in, for example, Japanese Unexamined Patent Application Publication No. 8-320486, in which an end face of a light guide, facing a light source, is inclined, thereby increasing the light introduced into the light guide. Another illumination device is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 8-335048, in which a reflective sheet is mounted on a face opposite a light-receiving face of a light guide.
As described above, there are various proposals for avoiding unevenness in light generation and increasing light strength of an illumination device. However, there has been a problem in that it is difficult to generate a planar light having high luminance in the known illumination devices.
Accordingly, an object of the present invention is to provide an illumination device which can form a planar light having high luminance. Another object of the present invention is to provide a liquid crystal apparatus which can perform significantly clear and uniform displays.
SUMMARY OF THE INVENTION
To these ends, a first illumination device according to the present invention comprises a light source; and a light guide for receiving light from the light source at a light-receiving face of the light guide and emitting the light from a light-emitting face of the light guide, wherein a face opposite the light-receiving face of the light guide is formed as an inclined face. That is, the face opposite the light-receiving face of the light guide is angled relative to the light-receiving face.
In the thus formed illumination device, the light, which has been introduced into the light guide from the light-receiving face of the light guide and reaches the inclined face opposite the light-receiving face without being emitted to the outside from the light-emitting face of the light guide, reflects at an angle rather than reflecting directly. As a result, the number of times of reflection of the light, which is being transmitted inside the light guide, increases, thereby increasing frequency in diffusion, whereby the light-emission efficiency improves and the luminance of emitted light increases. Unevenness in the luminance of the emitted light is decreased by increasing the number of times of reflection of the light which is being transmitted inside the light guide.
The angle of inclination of the inclined face of the first illumination device is studied, as follows. The angle of an inclined face
6
c
is set to a value &thgr; with respect to a plane Pn (plane which extends vertical in the drawing) normal to a light-emitting face
6
b
of a light guide
6
, as shown in FIG.
2
(
a
), and light-emission efficiency was obtained from the following expressions by performing a simulation.
Light-emission efficiency (%)=(emitted-light amount/incident-light amount)×100,
in which emitted-light amount=amount of light emitted from light-emitting face
6
b
, and
incident-light amount=amount of light incident to light-receiving face
6
a.
The result is shown in FIG.
7
(
a
). The angle &thgr; of inclination, in FIG.
2
(
a
), is shown in a positive value when the inclination is in the clockwise direction and in a negative value when the inclination is in the counterclockwise direction.
A graph shown in FIG.
7
(
b
) was obtained from the data of the result shown in FIG.
7
(
a
). It is known from the graph that the light-emission efficiency is low when the angle &thgr; of inclination of an end face
6
c
opposing the light-incident side of the light guide
6
shown in FIG.
2
(
a
) is 0°, as in a case of the known illumination device. As the angle of inclination of the end face increases, the light-emission efficiency gradually improves until the angle of inclination becomes approximately ±10°. However, the light-emission efficiency gradually decreases when the angle of inclination exceeds approximately ±10°.
That is, when the face
6
c
opposite the light-receiving face
6
a
of the light guide
6
is formed as an inclined plane, high light-emission-efficiency can be obtained when the angle &thgr; of inclination of the inclined face
6
c
is within a proper range. On the
Kawakami Hisanori
Takemura Masanori
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