Illumination – Revolving
Reexamination Certificate
1999-11-30
2001-03-27
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S027000, C362S331000
Reexamination Certificate
active
06206535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a planar lighting device such as a back-lighting device in a liquid crystal display, for exiting illuminating light from a light exit surface of a light guide member by scattering rays of light incident on the light guide member from a light source.
2. Description of the Prior Art
As a planar lighting device such as a back-lighting device in a liquid crystal display, the planar lighting device has hitherto been well known which comprises a flat plate-like light guide member and a tubular light source disposed adjacent and in face-to-face relation with an end face of the light guide member, wherein rays of light from the light source are, after having entered the light guide member, scattered to allow illuminating light to emerge outwardly from the light exit surface of the light guide member to thereby uniformly illuminate the liquid crystal display from behind. In recent years, demand for increase of the size of the planar lighting device with an increased surface area of the light exiting surface of the light guide member has arisen intensively along with demand for reduction in thickness thereof and, therefore, the uniformity of brightness compatible with increase in size and reduction in thickness is required.
FIG. 13
illustrates the first planar lighting device according to the prior art, which comprises a light guide member
42
in the form of a transparent resin plate such as an acrylic resin plate having a high light transmissivity and two light sources
4
such as cold-cathode tubes each positioned adjacent a corresponding end face
46
of the light guide member
42
and covered by a reflective plate
27
. This first prior art flat lighting device is such that while a reflecting surface
44
of the light guide member
42
is provided with a finely dotted irregular reflecting layer
29
formed by the use of a screen printing technique or a shot-blasting technique so that rays of light incident upon and propagating in the transparent resin plate
42
from the light sources
4
can be reflected to emerge outwardly from the light exit surface
45
. The planar lighting device in which the irregular reflecting layer is formed on one surface of the transparent resin plate has an advantage in that it can be manufactured having a reduced thickness.
There is also known the second prior art planar lighting device which comprises, as shown in
FIG. 14
, a wedge-shaped light guide member
70
prepared from a transparent resin mixed with scattering particles having an index of refraction different from that of the transparent resin, and a tubular light source such as a cold-cathode tube disposed adjacent and in face-to-face relation with one end face
70
a
of the light guide member
70
. The flat plate-like light guide member in which in place of the light guide member in the second-mentioned prior art planar lighting device wedge-shaped light guide sections are overlapped one above the other in the direction of thickness thereof as shown in FIG.
15
. This third-mentioned prior art planar lighting device shown in
FIG. 15
comprises a light guide plate
80
including a first light guide section
80
A made of a transparent resin (a non-scattering light guide region) and a second light guide section
80
B made of a transparent resin mixed with scattering particles having an index of refraction different therefrom (a scattering light guide region), and is disclosed in, for example, the U.S. Pat. No. 5,899,552.
Yet, the Japanese Laid-open Patent Publication No. 6-324330 discloses a fourth prior art planar lighting device comprising a light guide plate
90
including two wedge-shaped light guide sections
90
A and
90
B made of respective transparent resins containing a different concentration of scattering particles and, hence, having a different light scattering power, which wedge-shaped light guide sections
90
A and
90
B are overlapped one above the other in the thicknesswise direction thereof. In the third- and fourth-mentioned prior art planar lighting devices wherein the plural light guide plates having a different light scattering power are employed, as compared with the second-mentioned prior art planar lighting device, the light scattering power can be adjusted over the entire area of the light exit surface of the light guide plate and, therefore, the uniformity of brightness can easily be secured where the surface area of the light exit surface is relatively small.
The fifth prior art planar lighting device that satisfies the requirement of increase in size and reduction in thickness is illustrated in FIG.
17
. This fifth prior art planar lighting device shown in
FIG. 17
comprises a light guide member
50
formed to a shape similar to the prism-like hill corresponding to two light guide members
51
combined together, which light guide members
51
are similar to the wedge-shaped light guide sections
51
A and
51
B employed in the fourth prior art planar lighting device shown in
FIG. 16
, and two light sources
4
and
4
disposed adjacent and in face-to-face relation to opposite end faces
50
a
of the light guide member
50
.
The planar lighting device formed in a hill-like shape with a polygonal pyramid and having a light source disposed adjacent and in face-to-face relation with each end face thereof is effective to provide a high luminance when rays of light are incident thereupon through the end faces. The hill-like shape may be a shape of, for example, a triangular pyramid and a square pyramid, and an extremely flattened hill-like shape can be obtained with respect to the requirement of the thickness being reduced. As a sixth prior art flat lighting device, a light guide member formed into, for example, a hill-like shape similar to the shape of a square pyramid is shown in
FIG. 18A
in a perspective representation.
FIG. 18B
is a cross-sectional representation of the light guide member
10
taken along the line IV—IV in FIG.
18
A. This light guide member
10
includes a first light guide section (a non-scattering region)
11
having a recess of a shape similar to the inverted shape of a square pyramid and a second light guide section (a scattering region)
12
having a protrusion of a shape similar to the shape of a square pyramid.
As a method of making the light guide member used in the third to sixth prior art flat lighting devices, a method is known wherein, for example, two light guide sections are separately molded and are subsequently bonded together by the use of a bonding agent or the like.
Any of the first and second prior art planar lighting devices discussed above is suited where the light exit surface area is relatively small and, if the light exit surface is increased to increase the size of the planar lighting device, difficulty will arise in that a high brightness and a uniformity in luminance can no longer be secured. In other words, with the first prior art planar lighting device, in order to compensate for a phenomenon in which the brightness decreases with increase of the distance from the light source, the irregular reflectance is varied in unison with the light guiding distance (the distance from the end face of the light guide member), that is, the number of irregular reflecting layers is necessarily increased with increase of the distance away from the light source, and therefore, it is not easy to secure the uniformity in luminance. With the second prior art planar lighting device, since the single light source is employed, no high brightness can be obtained.
As regards the third prior art planar lighting device, as will be discussed in detail later, the first light guide section (a non-scattering light guide region)
80
A and the second light guide section (a scattering light guide region)
80
B are separately molded and are then bonded together by the use of a bonding agent or the like and, therefore, the workability is low since the both are bonded together after the molding, accompanied by increase in manufacturing cost. Also, since the bondin
Hattori Yukitoshi
Morino Masaya
Nakayama Hiroshi
Sakai Takeya
Hayashi Telempu Co., Ltd.
O'Shea Sandra
Sawhney Hargobind S.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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