Illumination – Revolving
Reexamination Certificate
1997-03-31
2003-11-04
Sember, Thomas M. (Department: 2875)
Illumination
Revolving
C362S327000, C362S330000, C362S339000
Reexamination Certificate
active
06641274
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a surface light source device, and more particularly to a surface light source device of the type in which directivity of illumination light is modified by at plate-shaped optical block. This invention is useful when applied to back lighting arrangement of a liquid crystal display and the like.
Surface light source devices of the type in which the direction of illumination light is corrected by a plate-shaped optical block are currently known and have been used in, for example, back lighting arrangement of a liquid crystal display. In a conventional surface light source device, a primary light source is disposed behind a plate-shaped optical member and, on the other hand, a light control member for modifying directivity of emitted light is disposed along an emitting surface of the plate-shaped optical member. In another conventional surface light source device, a primary light source is disposed near the side surface of a plate-shaped optical member and, on the other hand, a light control member for modifying directivity of emitted light is disposed along an emitting surface of the plate-shaped optical member. The latter device is called a sidelight-type surface light source device.
A typical primary light source to be used in a sidelight-type surface light source device is a rod-shaped light source. The rod-shaped light source is disposed along an end surface (incidence surface) of a plate-shaped optical member called the “light guide”. Illumination light emitted from the primary rod-shaped light source is introduced into the light guide plate from an end surface (incidence surface) of the light guide plate. The illumination light is deflected in the light guide plate and is then emitted from the major surface (emitting surface) of the light guide plate. The emitted illumination light is used in, for example, back lighting of a liquid crystal panel. Generally, since a primary light source is disposed on the side of a light guide plate, a sidelight-type surface light source device can have a thin-type structure.
Known light guide plates to be used in the sidelight-type surface light source device include a light guide plate having a substantially uniform thickness and a light guide plate having a varying thickness gradually decreasing as the distance from the primary light source increases.
FIG. 17
is an exploded perspective view of a conventional sidelight-type surface light source device. As shown in
FIG. 17
, a sidelight-type surface light source device
1
comprises a light scattering guide plate
2
, a primary light source
3
disposed on the side of the light scattering guide plate
2
, a reflection sheet
4
, and an optical block
5
as a light control member. The reflection sheet
4
, the light scattering guide plate
2
and the optical block
5
are placed one over another. The light scattering guide plate
2
is a light guide plate made of a conventional light scattering guiding material.
The primary light source
3
is composed of, for example, a cold cathode ray tube (fluorescent lamp)
6
and a reflector
7
in the form of a regular reflection member partially surrounding the cold cathode ray tube
6
. Illumination light is supplied from an opening of the reflector
7
toward an end surface (incidence surface) of the light scattering guide plate
2
.
The reflection sheet
4
is a regular reflection sheet such as a metal foil, or an irregular reflection sheet such as a white polyethyleneterephthalate (PET) film. The reflection sheet
4
serves to return illumination light which is leaked from the light scattering guide plate
2
to the light scattering guide plate
2
.
The light scattering guide plate
2
in the form of a wedge-shaped-cross-section light guide plate is composed of a matrix of, for example, polymechylmetacrylate (PMMA), and light-permeable particles different in index of refraction from the matrix and diffused uniformly in the matrix. As shown in
FIG. 18
, which is a cross-sectional view taken along line A—A of
FIG. 17
, illumination light L comes into the light scattering guide plate
2
from its one end surface near the primary light source, namely, an incidence surface T and propagates toward the wedge-shaped end as repeatedly reflected between a surface along the reflection sheet
4
and a surface along the optical block
5
. In this specification, the surface along the reflection sheet
4
is called “inclined surface”, and the surface along the optical block
5
is called “emitting surface”.
During this propagation, illumination light L undergoes scattering by the light-permeable particles. If the reflection sheet
4
is irregular-reflective, it also causes irregular reflection. It should be noted that the incidence angle of illumination light L gradually decreases with respect to the emitting surface as the illumination light L is repeatedly reflected at the inclined surface.
Illumination light component whose incidence angle is less than the critical angle with respect to the emitting surface is emitted from the emitting surface. Thus the illumination light L emitted from the emitting surface has a characteristics tending to be scattered due to the light-permeable particles and also due to the reflection sheet
4
, if the reflection sheet
4
is irregular-reflective. It is a common knowledge that, as is shown on an enlarged scale as indicated by an arrow B in
FIG. 18
, the main emitting direction of this illumination light L tends to be inclined to the end. This tendency or characteristics is called a “directional-emission characteristics” of the surface light source device or the light guide plate. Namely, the sidelight-type surface light source device
1
has a directional-emission characteristics.
The optical block
5
serves to modify this directivity. The optical block
5
may be made of light-transmission resin such as acrylic resin. The cross-sectional shape of the optical block
5
is designed in such a manner that the thickness varies complementarily with respect to the thickness of the light scattering guide plate
2
. Namely, the thickness of the optical block
5
increases as the distance from the incidence surface of the optical scattering guide plate
2
increases.
The optical block
5
is has an inner surface facing the light scattering guide plate
2
, and an outer surface facing in a direction opposite to the light scattering guide plate
2
. A prism surface is formed on each of the inner and outer surface of the optical block
5
. The prism surface is in the form of a repetition of triangular-cross-section projections each having a pair of inclined surfaces.
The rows of projections of the inner prism surface and the rows of projection of the outer prism surface extend perpendicularly to each other. The optical block
5
is oriented in such a manner that each row of projection of the inner prism surface extends parallel to the incidence surface, while each row of projection of the outer prism surface extends perpendicularly to the incidence surface.
As is shown on an enlarged scale as indicated by an arrow B in
FIG. 18
, the inner prism surface modifies directivity of emitted light, which is inclined from the incidence surface T toward the wedge-shaped end, into the frontal direction of the emitting surface. On the other hand, as is shown on an enlarged scale as indicated by an arrow C in
FIG. 18
, the outer prism surface modifies expansion of illumination light in the direction parallel to the incidence surface T. The direction from the incidence surface T toward the wedge-shaped end is hereinafter called the Y direction, and the direction parallel to the incidence surface T is hereafter called the X direction.
The light guide plate having a directional-emission characteristics the above-mentioned light scattering guide plate and a light guide plate made of transparent or semitransparent material and having a wedge-shaped or a approximately wedge-shaped cross section as well as a flat guide plate having on the incidence surface and/or rear surface a diffusion film
Masaki Kayoko
Sasako Hiromi
Enplas Corporation
Sember Thomas M.
Staas & Halsey , LLP
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