Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
1998-11-03
2002-05-07
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S061000, C362S026000, C362S027000, C362S035000
Reexamination Certificate
active
06384881
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention relates to a surface light source device of side light type and a liquid crystal display employing the surface light source device in its backlighting arrangement. For instance, the present invention relates to a liquid crystal display provided with a liquid crystal display panel employing TN liquid crystal.
2. Related Art
Surface light source devices of side light type have been conventionally employed, for instance, to illuminate a liquid crystal display panel from its back. This arrangement is suitable for making the overall structure thin.
In general, the light source device of side light type comprises a rod-shaped light source such as a cold cathode tube as a primary light source, which is arranged beside a guide plate (i.e. plate-shaped light guide). The primary light source emits illumination light which is introduced into the guide plate through a side end face (i.e. incidence face) thereof. Such introduced light propagates inside of the guide plate while outputting emission from a major face (i.e. emission face) toward a liquid crystal display panel.
Known types of guide plates employable in light source devices of side light type are, one having a substantially uniform thickness and another having a tendency to reduce thickness according to distance from the primary light source. The latter provides emission, in general, more effectively in comparison with the former. Light scattering-and-guiding material or transparent resin is employed as a material of these guide plates.
A guide plate made of light scattering-and-guiding material is called a “scattering guide plate”. A scattering guide plate is composed of a matrix, such as PMMA (polymethlyl methacrylate), and a great number of light-permeable fine particles which are dispersed uniformly therein. The fine particles are different from the matrix in refractive index.
FIG. 11
is an exploded perspective view illustrating a conventional light source device of side light type which employs a guide plate of the latter sort.
FIG. 12
is a cross section along line
12
—
12
in FIG.
11
.
Referring to FIG.
11
and
FIG. 12
, a light source device of side light type
1
comprises a guide plate
2
, a primary light source
3
, a reflection sheet
4
and a prism sheet
6
which is functioning as a light control member. The reflection sheet
4
, guide plate
2
and prism sheet
6
are laminatedly arranged. The primary light source
3
is disposed beside the guide plate
2
.
The guide plate
2
is made of a scattering-and-guiding material with a wedge-shaped cross section, being called a scattering guide plate. The scattering-and-guiding material is composed of a matrix, such as PMMA (polymethyl methacrylate), and a great number of light-permeable fine particles which are dispersed uniformly therein. The fine particles are different from the matrix in refractive index.
The primary light source
3
includes a cold cathode tube (fluorescent lamp)
7
backed by a reflector
8
which is generally semi-circular in cross section. Illumination light is supplied to a side end face, an incidence face
2
A, of the scattering guide plate
2
through an opening of the reflector
8
. The reflection sheet
4
is a sheet-like member with regular reflectivity such as metal foil or with irregular reflectivity such as white PET film.
Illumination light L is introduced into the guide plate
2
through the incidence face
2
A and propagates toward a distal end while repeating reflections at two major faces (back face
2
B and emission face
2
C). Illumination light is therewith subject to scattering effect of the fine particles within the guide plate
2
. If the reflection sheet
4
is an irregular reflection member, there will be an added irregular reflection effect.
Repeated reflections by the inclined back face
2
B will give the illumination light reducing incidence angles with respect to the emission face
2
C. Such reduction in incidence angle brings increased components which are angularly smaller than the critical angle with respect to the emission face
2
C, thereby promoting emission from the emission face. This prevents emission intensity from being insufficient in an area distant from the primary light source
3
.
The emission face
2
C outputs illumination light which assumes scattering light because it has undergone scattering effect of the fine particles within the guide plate
2
and, in some cases, further has undergone irregular reflection effect of the reflection sheet
4
.
However, illumination light outputted from the emission face
2
C has a principal propagation direction inclined toward the distal end with respect to the frontal direction in a plane perpendicular to the incidence face
2
A (i.e. inclined toward a direction as distancing the incidence face
2
A). That is, the output light of the scattering guide plate
2
has directivity. This property is called “emission directivity”.
The prism sheet
6
disposed along the emission face
2
C is a light-permeable sheet made of, for instance, polycarbonate. The prism sheet
6
is provided with a prismatic surface including a great number of parallel prismatic rows. In the illustrated example, the prism sheet
6
is arranged in an orientation such that the prismatic surface is directed toward the guide plate
2
and the prismatic rows run generally parallel (within an angular range about 0 to 15 degrees) to the incidence face
2
A.
Each prismatic row is a fine projection row such as one having a triangular cross section. Slopes of the projections correct obliquely emitted light toward the frontal direction in a plane perpendicular to the incidence face
2
A.
A double-surfaces prism sheet with prismatic surfaces on both faces may be employed. In the case, prismatic rows on its outer face run generally at right angles with ones on its inner face. The prismatic rows on the outer face correct light angularly toward the frontal direction in a plane parallel to the incidence face
2
A.
FIG. 13
is an exploded perspective view illustrating another conventional light source device of side light type.
FIG. 14
is a cross section along line
14
—
14
in FIG.
13
. In this example, a transparent guide plate is employed.
Referring to FIG.
13
and
FIG. 14
, a light source device of side light type
10
comprises a guide plate
12
, a primary light source
3
, a reflection sheet
4
, a light diffusion sheet
13
and prism sheets
14
,
15
. The reflection sheet
4
, guide plate
12
, light diffusion sheet
13
and prism sheets
14
,
15
are laminatedly arranged.
The guide plate
12
is made of a molded body of transparent acrylic resin, having a wedge-shaped cross section. The guide plate
12
has major faces to provide a back face
12
B and an emission face
12
C. A great number of dot-like light diffusion elements form a pattern on the back face
12
B, thereby providing a light diffusible surface. In order to achieve uniform brightness, the dot pattern is formed so that diffusing power rises according to distance from an incidence face
12
A. For instance, a covering rate of the dot pattern is adjusted so as to increase according to distance from the incidence face
12
A.
The primary light source
3
and the reflector
4
are the same as those shown in
FIGS. 11 and 12
. Illumination light L emitted from the primary light source
3
is introduced into the guide plate
12
through the incidence face
12
A. Such introduced light L propagates toward a distal end while repeating reflections at the back face
12
B, along which the reflector is disposed, and the emission face
2
C. On the way, illumination light L is subject to scattering effect of the back face
12
B which is provided with diffusibility. If the employed reflection sheet
4
has irregular reflectivity, irregular reflection will be effected.
Repeated reflections by the inclined back face
12
B will give the illumination light reducing incidence angles with respect to the emission face
12
C. Such reduction in incidence angle brings increased components which are angu
Arai Takayuki
Ohkawa Shingo
Chowdhury Tarifur R.
Enplas Corporation
Sikes William L.
LandOfFree
Surface light source device of side light type and liquid... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surface light source device of side light type and liquid..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface light source device of side light type and liquid... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2823771