Illumination – Revolving
Reexamination Certificate
2001-04-11
2004-09-14
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S560000, C362S561000, C362S551000, C362S558000, C362S023000, C362S026000, C362S027000, C349S065000
Reexamination Certificate
active
06789910
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination apparatus for illuminating an image display plane of a liquid crystal display device, and more specifically, relates to a scheme intended to realize a uniform in-plane brightness of the illumination apparatus in a method for converting a point light source into a plane light source. By means of the present invention, an illumination apparatus capable of emitting light as a plane light source with no unevenness in brightness can be realized even when a point light source is employed. In addition, by means of the present invention, an illumination apparatus capable of emitting light as a plane light source with less unevenness in brightness can be realized even when the small number of point light sources is employed.
2. Description of the Related Art
A liquid crystal electro-optical device is widely used in view of advantages of low power consumption, light weight, and a small thickness. The liquid crystal electro-optical device includes a direct-view type liquid crystal electro-optical device and a projection-type liquid crystal electro-optical device. In the case of a direct-view and transmission type liquid crystal electro-optical device, a viewer recognizes an image by means of a back light. In the case of a direct-view and reflection type liquid crystal electro-optical device, a viewer recognizes an image by means of a front light.
FIG. 22
shows a perspective view of an edge-light type back light in which light sources are disposed at side surfaces of a plate-like light guiding plate. More specifically, the light sources
104
, each of which is a line light source such as a cold cathode fluorescent tube or the like, are provided at two opposite side surfaces of the plate-like light guiding plate
105
. Light incident onto the plate-like light guiding plate
105
is scattered by means of ink dots
106
formed on a rear surface of the plate-like light guiding plane to emit toward a transmission type liquid crystal electro-optical device
101
. A prism sheet
103
may be used over the plate-like light guiding plate in order to enhance brightness in the front direction. Light emitted from the plate-like light guiding plate and provided with directionality by means of the prism sheet is incident on a diffusion plate
102
so that the in-plane brightness distribution can become uniform by means of the diffusion plate. Light scattered by the ink dots and leaked downward from the plate-like light guiding plate is reflected by reflecting plate
107
to travel back toward the liquid crystal electro-optical device
101
.
Thus, the illumination apparatus such as a back light is provided with a plate-like light guiding plate disposed below a display region of a liquid crystal electro-optical device, and further provided with line light sources disposed at the side surfaces of the plate-like light guiding plate. Light emitted from the light sources repeats total reflections within the plate-like light guiding plate to be expanded over the entire region of the plate-like light guiding plate.
FIGS. 20A and 20B
respectively show cross-sectional views of the plate-like light guiding plate in the thickness direction thereof, illustrating different manners of light propagation in the plate-like light guiding plate. It should be noted that six surfaces are defined for the plate-shaped light guiding plate as shown in a perspective view of
FIG. 19A
, in order to explain the light propagation. More specifically, a surface closer to a viewer is referred to as an upper surface
735
, while a surface opposite to the upper surface is referred to as a lower surface
736
. A side surface onto which a light emitted from a light source
737
is incident is referred to as an end surface
738
. Each of surfaces perpendicular to the end surface is referred to as a side surface
739
. The last surface is a surface
740
, which is parallel to the end surface.
FIG. 20A
illustrates the light propagation in the case where light is incident along the end surface
109
of the plate-like light guiding plate having the refractive index of 1.49 from the air
112
having the refractive index of 1. The light incident along the end surface of the plate-like light guiding plate is refracted in accordance with the Snell's law to be propagated at the angle of 42° with respect to the normal direction of the end surface of the plate-like light guiding plate, and is then incident on the lower surface
110
of the plate-like light guiding plate at the angle of 48° which exceeds the critical angle, thereby being totally reflected. Thereafter, the light is incident on the upper surface
111
of the plate-like light guiding plate at the angle of 48° to be totally reflected. Thus, the light repeats the total reflections at the upper surface
111
of the plate-like light guiding plate and the lower surface of the plate-like light guiding plate.
FIG. 20B
illustrates the light propagation in the case where light is incident at the angle (&thgr;
1
) smaller than 90° with respect to the normal direction of the end surface
109
of the plate-like light guiding plate
105
having the refractive index of 1.49 from the air having the refractive index of 1. The light entering the plate-like light guiding plate is incident on the upper surface
111
of the plate-like light guiding plate and the lower surface
110
of the plate-like light guiding plate at the angle (&thgr;
2
), which exceeds the critical angle. Thus, the light repeats the total reflections at the upper surface of the plate-like light guiding plate and the lower surface of the plate-like light guiding plate, thereby resulting in the light being emitted from the surface parallel to the end surface
109
while being inclined at the angle of &thgr;
1
with respect to the normal direction of this surface.
Thus, the light incident on the end surface
109
of the plate-like light guiding plate at any angle is entirely totally reflected within the plate-like light guiding plate. Accordingly, no light is allowed to emit through the upper surface of the plate-like light guiding plate or the lower surface of the plate-like light guiding plate, so long as no structural member is provided at the upper or lower surface of the plate-like light guiding plate. In addition, as calculated from the Snell's law, the light incident from the air onto the end surface of the plate-like light guiding plate at any angle is refracted at the interface between the air and the end surface of the plate-like light guiding plate, so that the light propagating within the plate-like light guiding plate is inclined with respect to the normal direction of the end surface of the plate-like light guiding plate at 42° or less.
In the case where it is desired to emit the light through the upper surface of the plate-like light guiding plate, white-colored ink dots may be provided at the lower surface of the plate-like light guiding plate.
FIG. 23
illustrates a cross-sectional view of an edge-light type back light. Like reference numerals designate like components both in
FIGS. 22 and 23
. A light source
104
is provided in the vicinity of an end surface
109
of the plate-like light guiding plate, and a lamp reflector
108
is formed around the light source. Light emitted from the light source and light reflected from the lamp reflector are allowed to enter a plate-like light guiding plate through the end surface of the plate-like light guiding plate
105
. The light is incident on the upper surface
111
of the plate-like light guiding plate and the lower surface
110
of the plate-like light guiding plate to be totally reflected within the plate-like light guiding plate. However, since the white-colored ink dots
106
are printed on the lower surface of the plate-like light guiding plate, the light incident onto the ink dots
106
is scattered due to the shape or the refractive index of the ink dots. When the light is thus scattered by the ink dot and is allowed to be incident on the upper sur
Kimura Hajime
Satake Rumo
Fish & Richardson P.C.
Husar Stephen
Semiconductor Energy Laboratory Co,. Ltd.
Zeade B.
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