Illumination – Revolving
Reexamination Certificate
2002-03-11
2004-12-07
Husar, Stephen F. (Department: 2875)
Illumination
Revolving
C362S026000, C349S065000, C385S146000
Reexamination Certificate
active
06827458
ABSTRACT:
TECHNICAL FIELD
The present invention pertains to a planar light source device, and more particularly to a planar light source device utilizes a novel light guide pipe and light reflection sheet that are employed particularly favorably in an illumination optical system, and can be used favorably as a backlight optical system of a liquid crystal display device.
BACKGROUND ART
Recently, transmission-type liquid crystal display devices are frequently used as display devices in monitors designed for personal computers and in thin televisions and the like. In such liquid crystal displays, on a rear side of a liquid crystal element, there is normally arranged an illumination device, namely a backlight (a planar light source device). The planar light source device serves as a mechanism for converting a linear light source such as a cold cathode discharge tube, for example, into surface light.
Specifically, a method in which the light source is arranged directly below the rear side of the liquid crystal element, and a method in which the light source is arranged to a side surface and an acrylic plate or other such translucent light guide pipe is used to convert the light to the surface form to thus obtain the surface light source (a side light method), are representative. On a light radiation surface there is arranged an optical element composed of a prism array or the like, and this serves as a mechanism for obtaining desired optical characteristics.
In the conventional planar light source device using the side light method, as shown in
FIG. 44
, on one side edge or a substrate which is the light guide pipe
1
and is composed of a translucent plate, there is arranged a linear light source
2
arranged such that it lies along an end surface
1
a
of the side edge portion, and a reflector
3
is attached so as to cover the light source
2
. This serves as a mechanism in which direct light from the linear light source
2
and light reflected by the reflector
3
enter the light guide pipe
1
, into an inner portion thereof, from a light incidence end surface which is the side edge portion surface
1
a.
One surface
1
b
of the light guide pipe
1
serves as a light radiation surface, and on this light radiation surface
1
b
there is arranged a light modulation sheet
5
, on which is formed an array
4
in the form of substantially triangle prisms, of which top angles are directed toward a viewer. On the other hand, on a surface
1
c
of a side opposite from the light radiation surface
1
b
in the light guide pipe
1
, there is provided a light extracting mechanism
6
on which there are formed multiple dots
6
a
,
6
b
,
6
c
. . . printed in a predetermined pattern using light scattering ink.
In the light guide pipe
1
to which the above light extracting mechanism
6
is formed, on the surface
1
c
side that is opposite from the light radiation surface
1
b
there is provided a reflection sheet
7
in close proximity to this surface
1
c
. Further, as a different example of this type of conventional planar light source device, as shown in
FIG. 45
, the light modulating sheet
5
has the array
4
of substantially triangle prisms formed thereon, which is disposed above the light radiation surface
1
b
with the top angles of the triangle prisms facing toward the light radiation surface
1
b
of the light guide pipe
1
.
Further, a light extracting mechanism
8
, which is provided to the surface
1
c
being on the opposite side of the light guide pipe
1
from the light radiation surface, is composed of multiple protruding portions
8
a
,
8
b
,
8
c
. . . each having its surface formed as a rough surface. The planar light source devices according to the above side light method are capable of taking greater advantage of lightness and thinness, which are general characteristics of liquid crystal display devices, so they are frequently used as the backlight in liquid crystal displays of portable personal computers and the like.
However, in the conventional transmission-type liquid crystal display devices, there was the problem that the construction was still rather complicated. The reason for this was that, particularly in the planar light source device, it was not possible to obtain an illumination optical system having a simple structure and being capable of achieving the desired optical characteristics, so the structure of the planar light source device had to be made complex. The resultant increased costs and the like have prevented this type of liquid crystal display device from being widely used.
That is, in the planar light source devices shown in FIG.
44
and
FIG. 45
which were used as the backlight optical system in, say, the transmission-type liquid crystal display device, in order to make use of the illumination light from the planar light source device as effectively as possible, a prism sheet or other such optical sheet item was frequently used. Accordingly, the structure of the illumination optical system become complicated, and as a result, high costs were incurred due to difficult assembly as well as low yield.
The present invention was developed to solve the conventional problems; therefore, an object of the present invention is to provide an inexpensive planar light source device which is based on a novel, simply constructed illumination system that is superior in its efficiency of utilization of illumination light beams, uses a light reflection sheet that is a novel light guide pipe and novel light control member to thereby achieve effective utilization of light, and also has a structure that is simple and superior in easiness of assembly.
DISCLOSURE OF THE INVENTION
The present invention relates to a planar light source device, which is comprised as follows in order to solve the above-mentioned technical problem. That is, the planar light source device according to the present invention is comprising a light guide pipe formed as a plate (sheet) made of transparent synthetic resin with one surface thereof serving as a light radiation surface, and a light source arranged in the vicinity of at least one side edge portion of the light guide pipe; and light beams radiating out from the light radiation surface of the light guide pipe at the time when the light source is lit up has a peak of a distribution of radiation angles with respect to a right angle direction to the surface of the side edge portion of the light guide pipe to which the light source is arranged being within ±15° from a normal line (perpendicular line) of the light radiation surface, and a half-width of the distribution of radiation angles being within ±30°.
Further, a planar light source device according to the present invention is comprising a light reflection sheet arranged to an opposite surface side from the light radiation surface of the light guide pipe; light beams that have entered the light guide pipe from the light source are radiated out from the opposite surface from the light radiation surface, and are reflected at the light reflection sheet; the reflected light is again made to enter the light guide pipe and is radiated out from the light radiation surface of the light guide pipe; and the radiated light at that time has a peak of the distribution of radiation angles with respect to the right angle direction to the surface of the side edge portion of the light guide pipe being within ±15° from a normal line (perpendicular line) of the light radiation surface, and a half-width of the distribution of radiation angles being within ±30°.
Further, a planar light source device according to the present invention is comprising a light extracting mechanism provided to the opposite surface from the light radiation surface of the light guide pipe, and a light extracting mechanism makes a greater part of the light beams that have entered the light guide pipe from the light source radiate out from the opposite surface from the light radiation surface, and reflect at the light reflection sheet.
Furthermore, a planar light source device according to the present inven
Husar Stephen F.
Mitsubishi Chemical Corporation
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