Illumination – Revolving
Reexamination Certificate
2001-02-23
2002-10-15
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S241000, C362S027000, C362S248000, C362S237000
Reexamination Certificate
active
06464367
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a surface light system used for backlighting of liquid crystal displays or the like, and particularly to a so-called tandem type surface light source system.
As the surface light source system, there has been known a so-called tandem type surface light source system allowed to obtain a more uniform luminous intensity over a wider area.
A configuration of a related art tandem type surface light source system will be described below with reference to
FIGS. 1A and 1B
.
Referring to
FIG. 1A
, there is shown a surface light source system
1
including a plurality (three in the example shown in the figure) of fluorescent tubes
2
a
,
2
b
, and
2
c
which horizontally extend in the direction perpendicular to the longitudinal direction of the system
1
in such a manner as to be spaced from and in parallel to each other; light guide plates
3
a
,
3
b
, and
3
c
made from a transparent material, which extend along right or left sides (right sides in the example shown in the figure) of the fluorescent tubes
2
a
,
2
b
, and
2
c
; reflectors
4
a
,
4
b
, and
4
c
disposed on the opposed sides (left sides in the example shown in the figure) to the light guide plates
3
a
,
3
b
, and
3
c
in such a manner as to surround the fluorescent tubes
2
a
,
2
b
, and
2
c
; reflecting members
5
a
,
5
b
, and
5
c
disposed under the light guide plates
3
a
,
3
b
, and
3
c
; and a lens sheet
6
disposed over the light guide plates
3
a
,
3
b
, and
3
c.
Each of the light guide plates
3
a
,
3
b
, and
3
c
is formed into a shape in cross-section which tapers as a wedge in the direction from the corresponding one of the fluorescent tubes
2
a
,
2
b
, and
2
c
to the opposed side. In the example shown in the figure, the light guide plates
3
a
,
3
b
, and
3
c
are integrated with each other.
According to the surface light source system
1
having the above--configuration, light rays emitted from the fluorescent tubes
2
a
,
2
b
, and
2
c
directly enter the light guide plates
3
a
,
3
b
, and
3
c
or are reflected from the inner surfaces of the reflectors
4
a
,
4
b
, and
4
c
and enter the light guide plates
3
a
,
3
b
, and
3
c
; the light rays, which pass through the light guide plates
3
a
,
3
b
, and
3
c
, are reflected from the reflecting members
5
a
,
5
b
, and
5
c
to direct upwardly through the light guide plates
3
a
,
3
b
, and
3
c
, and are diffused by the lens sheet
6
; and the light rays thus diffused by the lens sheet
6
light a liquid crystal display (not shown) from the back surface thereof, for example.
The surface light source system
1
, however, has a problem. At the ends and their neighborhoods, on the fluorescent tube sides, of the light guide plates
3
a
,
3
b
, and
3
c
, part of light rays, which have entered the light guide plates
3
a
,
3
b
, and
3
c
from the fluorescent tubes
2
a
,
2
b
, and
2
c
directly or by way of reflection from the inner surfaces of the reflectors
4
a
,
4
b
, and
4
c
, may be directly emerged outside therefrom without total reflection at the top surfaces of the light guide plates
3
a
,
3
b
, and
3
c.
As a result, as shown in
FIG. 1B
, at the ends and their neighborhoods, on the fluorescent tube sides, of the light guide plates
3
a
,
3
b
, and
3
c
, the luminance becomes significantly higher, so that uneven luminance portions appear in the luminance distribution of the surface light source system
1
. To be more specific, on the top surface of the lens sheet
6
, luminance becomes higher at portions near the fluorescent tubes
2
a
,
2
b
, and
2
c
, with a result that there occurs large differences in luminance between the portions near the fluorescent tubes
2
a
,
2
b
, and
2
c
and other portions. In particular, if the light guide plates
3
a
,
3
b
, and
3
c
are divided from each other, bright lines and shades occur along the division lines, thereby failing to obtain a uniform surface light source.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tandem type surface light source system allowing a uniform luminance over the surface light source.
To achieve the above object, according to a first aspect of the present invention, there is provided a surface light source system including: a plurality of bar-like light sources disposed in parallel to each other; reflecting members, each of which is disposed to surround a right or left side, an upper side, and a lower side of the corresponding one of the light sources; light guide plates made from a transparent material, each of which is disposed along the left or right side of the corresponding one of the light sources, and is formed into a taper shape in cross-section along the traveling direction of light; and reflecting sheets, each of which is disposed on the back surface of the corresponding one of the light guide plates; wherein each of at least the second and later ones of the light guide plates is, at its end portion on the light source side, integrated with a light introducing portion made from a transparent material, the light introducing portion extending from the end portion, on the light source side, of the light guide plate to a position under an end portion of the front side light guide plate adjacent to the light guide plate.
With this configuration, the system functions as a surface light source as follows. Light rays enter the light introducing portions directly or indirectly, that is, by way of reflection from the inner surfaces of the reflecting members, being subjected to total reflection from the top or bottom surfaces of the light introducing portions, and enter the light guide plates. The light rays having entered the light guide plates travel throughout the light guide plates while being repeatedly subjected to total reflection from the top surfaces of the light guide plates and to reflection from the reflection sheets located on the back surfaces of the light guide plates, and are emerged from the top surfaces of the light guide plates.
As described above, the light rays having entered the light introducing portions are not directly emerged from the top surfaces of the light guide plates, and accordingly, it is possible to suppress occurrence of locally high luminous lines at ends and their neighborhoods, on the light source sides, of the light guide plates, which luminous lines have occurred in the related art system. This makes it possible to prevent occurrence of unevenness of luminance and hence to obtain a uniform luminance over the surfaces of the light guide plates.
In this system, each of at least the second and later ones of the reflecting sheets may extend along the back surface of the corresponding one of the light introducing portions. With this configuration, when the light rays, which have been emitted from the light sources and entered the light introducing portions, are emerged downwardly therefrom without total reflection from the bottom surfaces of the light introducing portions, the light rays thus emerged downwardly are returned in the light introducing portions by the reflecting sheets.
In the system, an end plane, on the light source side, of each of the light introducing portions may be formed with its upper end tilted in the direction of the light guide plate. With this configuration, since light rays having been emitted from the light sources enter the light introducing portions while being refracted downwardly, the light rays reflected from the bottom surfaces of the light introducing portions are made incident on the top surfaces of the light guide plates at small incident angles, to be thereby less subjected to total reflection from the top surfaces of the light guide plates. This is effective to prevent occurrence of shades at boundaries between the light guide plates.
In the system, a top surface or bottom surface of each of the light introducing portions may be subjected to a coarsening treatment. With this configuration, since light rays, which have been emitted from the light sources and entered
Ito Tomotaka
Yano Tomoya
Alavi Ali
O'Shea Sandra
Sonnenschein Nath & Rosenthal
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