Illumination – Revolving
Reexamination Certificate
2002-05-15
2003-09-09
Tso, Laura K. (Department: 2875)
Illumination
Revolving
Reexamination Certificate
active
06616290
ABSTRACT:
BACKGROUND
1. Field of Invention
The present invention relates to a light guide plate, surface light source device and liquid crystal display, in particular, to improvements of a light guide plate having a back face provided with a great number of micro-reflectors, a surface light source device employing the foresaid improved light guide plate and a liquid crystal display employing the surface light source device for illumination a liquid crystal display panel. The present invention is applied to liquid crystal displays for personal computers, car-navigation systems or portable telephones, being applied further to surface light source devices and light guide plates used therein.
2. Related Art
According to a well-known prior art, a surface light source device has a light guide plate which is supplied with light sideways and outputs the light through an emission face after introducing the light into the light guide plate and applying direction-conversion, being broadly employed for illuminating an LCD panel or other uses. Although rod-like fluorescent lamps (cold cathode tubes) have been used broadly as primary light sources, those using point-like light sources such as LEDs (Light Emitting Diodes) tend to be employed recently.
In such surface light source devices, the light introduced into a light guide plate is outputted from an emission face after being light-direction-converted. As known well, light-direction-conversion within a light guide plate and emission from an emission face are promoted by employing a light guide plate made of light scattering-guiding material, or by applying emission promoting processing such as making a back face or emission face light-diffusible.
However, as known well, such means causes the emitted light to be preferentially directed to much forward inclined directions (for example, about 60 degrees with respect to a frontal direction). Such greatly inclined output directions are much quite different from usually desired output directions, which are usually generally frontal directions or around them. According to a prior proposition to realize a direction-conversion capable of providing a preferential output direction which is desired, a great number of micro-reflectors are formed on a back face of a light guide plate.
The micro-reflectors on the back face of the light guide plate in accordance with the proposed art are shaped like a great number of micro-projections, which generate an inner propagation light proceeding toward an emission face by means of an innerface reflection of the projections. This inner propagation light is emitted from the emission face, becoming an output light. Here described is an example of arrangement comprising a light source device, which employs a light guide plate provided with micro-reflectors, for backlighting a liquid crystal display panel by referring to
FIG. 1
to FIG.
4
.
In the first place,
FIG. 1
a
is a back side plan view of an outlined arrangement of a surface light source device employing a light guide plate provided with micro-reflectors for backlighting of a liquid crystal display panel, and
FIG. 1
b
is a side view from the left side in
FIG. 1
a.
FIGS. 2
a
and
2
b
illustrate an array example of micro-reflector
20
in the arrangement. In these illustrations, a light guide plate denoted by reference numeral
10
is made of a transparent material such as acrylic resin, polycarbonate (PC) or cycloolefin-type resin, a side end face of which provides an incidence face
12
.
A rod-like primary light source (cold cathode tube) L
1
is disposed along the incidence face
12
which is supplied with light from the primary light source. The light guide plate
10
has major faces
13
and
14
one of which provides an emission face
13
. The other face (back face)
14
is provided with a great number of micro-reflectors
20
shaped like micro-projections.
A well-known liquid crystal display panel PL is disposed on the outside of the emission face
13
to provide a liquid crystal display of backlighting type. It is noted that the micro-reflectors
20
are not shown in
FIG. 1
a.
Size values are merely examples, being indicated in mm.
The primary light source L
1
emits light, which is introduced into the light guide plate
10
through the incidence face
12
. An inner propagation light travels within the light guide plate
10
and undergoes direction-conversion on entering into micro-reflectors
20
through inner-reflections by inner faces of projections, with the result that light proceeding toward the emission face
13
is produced. Such inner reflection occurs twice generally as described later.
An example of arrangement of micro-reflectors
20
on the back face
14
of the light guide plate
10
is shown in
FIGS. 2
a
and
2
b.
It is noted that the primary light L
1
disposed along the incidence face
12
is a rod-like cold cathode tube having an emitting portion length of which is somewhat smaller than that of the incidence face
12
. Both ends are electrode portions EL
1
and EL
2
which are incapable of emitting light. Such a design is adopted often in order to avoid the electrode portions EL
1
and EL
2
of both ends from protruding.
Micro-reflectors
20
are distributed on the back face
14
so that covering rate tends to increase according to an increasing distance from the incidence face
12
.
Micro-reflectors
20
are arranged in corner area C and D located close to the electrode portions EL
1
and EL
2
, respectively, at a specifically large covering rate. Such a covering rate distribution prevents brightness from varying depending on distance from the incidence face
12
and from being short in the corner areas. It is noted that “covering rate” of micro-reflectors is defined as area occupied by micro-reflectors per unit area of a back face of a light guide plate.
Each micro-reflector
20
is shaped like a quadrangle-pyramid, projecting from a general plane representing the back face
14
(i.e. a plane formed by provisionally removing the micro-reflectors
20
). Each micro-reflector
20
has a posture determined as to cause light approaching there to be inner-inputted efficiently and to be converted into an inner output light proceeding generally at right angles with respect to the emission face
13
. Such processes are described with referring to
FIGS. 3
,
4
a
,
4
b
and
4
c.
FIG. 3
shows one of the micro-reflectors
20
with an illustration of direction conversion of an inner propagation light effected by the micro-reflector. In the illustration, the inner propagation light is represented by representative light beams P
1
and P
2
. Beam P
1
represents an inner propagation light which is reflected by the slope
21
and then by the slope
22
in order while beam P
2
represents an inner propagation light which is reflected by the slope
22
and then by the slope
21
in order. Beams QI and Q
2
represent inner output light beams produced from beams P
1
and P
2
, respectively.
It is noted that a pair of beams P
1
and P
2
run in parallel with a main approaching direction of light which is inner-inputted in a corresponding micro-reflector
20
. In
FIG. 3
, coordinate O-XYZ is a right-hand coordinate used to denote directions, Z-axis of which extends vertically to the emission face
13
(more precisely, a second general plane representing the emission face; in the same way, hereafter) and has a +Z-direction that corresponds to a “frontal direction”.
X-axis is perpendicular to both Z-axis and the incidence face
12
, having an orientation (plus-minus sign) such that +X-direction extends as to get farther from the incidence face
12
. Y-axis runs at right angles with respect to both Z-axis and X-axis as to provide a right-hand rectangular Cartesian coordinate O-XYZ (having original O optionally positioned), extending in parallel with the incidence face
12
.
For the sake of description in the instant specification, a rectangular Cartesian coordinate O-xyz, which is independent of coordinate O-XYZ, is defined for each micro-reflector. Defined are x-axis, y-axis and z-axis
Enplas Corporation
Staas & Halsey , LLP
Tso Laura K.
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