Illumination – Revolving
Reexamination Certificate
2001-12-18
2004-06-08
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S026000, C362S033000, C362S296040, C362S307000, C362S308000, C362S328000, C362S329000, C349S062000, C349S063000, C349S064000, C349S065000
Reexamination Certificate
active
06746130
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention relates to a light control sheet to direction-control an angularly extending light inputted from an oblique direction so that an output light is directed to an desired direction, also relating to a surface light source device and LCD using the light control sheet. The present invention is applicable to general light controls and various devices which require an illumination light extending like a face, for example, display incorporated in a personal computer or car navigation system.
2. Related Art
A proposed surface light source device employs a light guide plate made of a transparent light guiding material or light scattering-guiding material and a prism sheet, being broadly applied to various uses such as backlighting of liquid crystal display. A prism sheet is a most popular light control sheet which is used for direction-control an obliquely inputted light so that an output light is directed to an desired direction. A prism sheet is made of a light-permeable material having a prismatic surface provided with a great number of prism-like projection rows.
FIG. 1
a
is a partially exploded view illustration an outlined structure of a liquid crystal display provided with a backlighting arrangement in which a surface light source device of side light type employing a conventional and usual prism sheet, and
FIG. 1
b
is a partially enlarged cross section view a part of the liquid crystal display. It is noted that thickness of a prism sheet
4
or other members, formation pitch an depth of prism elements and so forth are exaggerated for the sake of illustration.
Referring to the figures, reference numeral
1
denotes a light guide plate that is an optical member formed of transparent light guiding material or light scattering-guiding material and having a wedge-like cross section. Light scattering-guiding material is a well-known optical material having both light-guiding function and inner-scattering function, being made of, for instance, matrix of polymethyl methacrylate (PMMA) and “substance having a different refractive index” which is uniformly disposed in the matrix. It is noted that “substance having a different refractive index” is substance having a refractive index substantially different from that of the matrix.
A thicker end face of the light guide plate
1
provides an incidence end face
2
near to which a primary light source element (fluorescent lamp) L backed by a reflector R is disposed. The light guide plate
1
has major faces, one (front face) providing an emission face
5
, the other (rear face) providing a back face
6
. A reflector
3
is disposed along the back face
6
. The reflector
3
is formed of silver foil with regular reflectivity or white sheet with diffusive reflectivity.
Ae known well, the emission face
5
emits an emission flux having a n obliquely-forwarding directivity. The prism sheet
4
is arranged on the outside of the emission face
5
so that a prismatic face (light input face) is directed inward.
Referring to the partially-exploded illustration, a light output face (outer face)
4
c
provides a flat surface. On the outside of the light output face
4
c
disposed is a liquid crystal display panel LP and a polarization separating sheet LS which is interposed between the light output face (outer face)
4
c
and the liquid crystal display panel LP. The liquid crystal display panel LP has a well-known structure such that elements such as liquid crystal cell and transparent electrodes are interposed between two polarizing plates arranged so that their polarization axes make the right angle with each other.
The polarization separating sheet LS is an optical element that tends to be used currently, being disposed between a polarizing plate on the inside of the liquid crystal display panel LP and the prism sheet
4
. The polarization separating sheet LS has a property that shows a high transmissivity for a polarization component parallel to a polarization axis of the polarizing plate on the inside of the liquid crystal display panel LP and shows a high reflectivity for a polarization component perpendicular to the polarization axis of the polarizing plate on the inside of the liquid crystal display panel LP.
It is noted that a space (air layer), not shown, is formed between the liquid crystal display panel LP and the polarization separating sheet LS or between the liquid crystal display panel LP and the prism sheet
4
(if no polarization separating sheet is employed), as required, in order to prevent these members to be stuck to each other.
The prism sheet
4
has an input face provided by a prism surface having a great number of prism element rows. These prism element rows are orientated generally in a direction parallel to the incidence end face
2
of the light guide plate
1
. As shown in a partially enlarged cross section
FIG. 1
b,
each prism element row a pair of slopes
4
a
and
4
b
which provides a V-shaped groove.
Angle &phgr;a is defined as an inclination angle of a first slope
4
a
directed toward the side of the incidence end face
2
and &phgr;b is defined as an inclination angle of a second slope
4
b
directed to the opposite side. Angles &phgr;a and &phgr;b are measured with respect to a frontal direction (See reference N), respectively. A prism sheet that satisfies a condition, substantially &phgr;a=&phgr;b (0 degree≦&phgr;a<90 degrees), is called “symmetric prism sheet” and a prism sheet that satisfies a condition, substantially &phgr;a≠&phgr;b, is called “asymmetric prism sheet”. An asymmetric prism sheet is disclosed in WO98/40664.
Light is introduced into the light guide plate
1
from the light source element L, being guided toward a thinner side end face
7
with repeated reflections at the emission face
5
and back face
6
. On the way of this travelling, illumination light is emitted from the emission face (front face)
5
gradually. The emission face
5
may have a matted surface or inner scattering may be utilized (if light scattering guide is employed) in order to promote emission.
As known well, the emission face
5
provides emission which shows a clear directivity to a direction inclined forward as a whole (Emission directivity of light guide plate). It is noted that such emission directivity may be relaxed if the emission face
5
or the back face
6
is provided with light diffusibility.
FIG. 2
is a graph showing angular intensity characteristics of emission from an emission face
5
of a typical light guide plate (transparent light guide plate having a matted emission face). In the graph, the abscissa shows directions in a plane perpendicular to the incidence end face
2
. Angle indication of 0 degree denotes a frontal direction, and minus values correspond to the side of incidence end face
2
and plus values correspond to the side of distal end (forward side). The ordinate shows luminance in unit “a.u.” that is defined so that the peak value is just “1.0”.
As understood from this graph, the emission flux has a remarkably clear directivity such that a peak direction (emission angle of a main beam) is somewhat greater than 70 degrees. In general, angular position of peak direction may vary in a variation range from several degrees to ten and several degrees in dependence on factors such as size or material (transparent material or light scattering guide) of the light guide plate, properties of the emission (ability of light scattering) face and back face, and property of the reflection sheet disposed on the side of the back face. However, in general, there are no great difference among curves of graph provided in the respective cases.
FIG. 3
is a diagram illustrating a fundamental operation of the light control sheet
4
, which is conventionally used, wherein it is provided that the light guide plate
1
has emission directivity of as described.
Referring to
FIG. 3
, the prism sheet
4
is disposed along the emission face
5
of the light guide plate
1
so that the prismatic surface is directed inward. Each prism element has a
Enplas Corporation
O'Shea Sandra
Staas & Halsey , LLP
Tsidulko Mark
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