Illumination – Revolving
Reexamination Certificate
2000-07-12
2002-06-18
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C349S065000, C362S551000, C362S561000
Reexamination Certificate
active
06406160
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sheet-like light source device. More particularly, it relates to a sheet-like light source device which is employed as a backlight of a liquid crystal display device, wherein the sheet-like light source device is capable of eliminating irregularities in brightness generated at peripheries of electrode portions of a rod-like light source such as a lamp.
A sheet-like light source device as illustrated in
FIGS. 5 and 6
is conventionally used a backlight in a liquid crystal display device. Such a conventional sheet-like light source device is composed of a lamp
21
serving as a rod-like light source, a lamp reflector
22
serving as a tubular reflection member, a light-conducting plate
23
, and a reflecting sheet
24
serving as a planar reflecting member. The lamp
21
mainly comprises a cold-cathode tube (CFL), and light emitted from the lamp
21
is made incident on the light-conducting plate
23
, either directly or via the lamp reflector
22
. A transparent material is used as the light-conducting plate
23
, and polymethyl methacrylate (PMMA) exhibiting high transmission rate of light is generally used. As illustrated in
FIG. 6
, light which is made incident on a light-incident surface
23
a
of the light-conducting plate
23
at an angle of &thgr;
21
is refracted, and its angle &thgr;
22
within the light-conducting plate
23
will be in a range of 0 to 42° owing to Snell's law of fraction. Light will thereafter hit against a front surface
23
b
or rear surface
23
c
of the light-conducting plate
23
, wherein the incident angle &thgr;
23
is represented by 90°-−&thgr;
22
and will be in a range of 48 to 90°. Since a total reflection angle of PMMA is 42°, &thgr;
23
will be a total reflection angle. In other words, all of light made incident from the light-incident surface
23
a
of the light-conducting plate
23
will satisfy a total reflection condition and will not be emitted from the front surface
23
b
or rear surface
23
c
of the light-conducting plate
23
. The rear surface
23
c
of the light-conducting plate
23
is thus devised to emit light therefrom to the front surface
23
b
by forming a scattering portion
25
generally through white printing. Light will be scattered when hitting against this scattering portion
25
to thereby break the total reflection condition of light within the light-conducting plate
23
, so that light will be emitted from the front surface
23
b
which is a display surface side of the light-conducting plate
23
. This scattering portion
25
is made of a material which does not perform absorption, but only perform scattering of light. Light which has been scattered at the scattering portion
25
will be also scattered to the rear surface
23
c
which is a non-display surface side of the light-conducting plate
23
, so that a reflecting sheet
24
is placed on the rear surface
23
c
for reflecting this light to the front surface
23
b
on the display surface side. The reflecting sheet
24
is generally disposed to extend to the interior of the lamp reflector
22
as illustrated in FIG.
6
.
Accompanying downsizing of personal computers in these years, narrow framing (that is, decreasing the width of frame
26
as illustrated in
FIG. 7
) of liquid crystal display devices is also being strongly wanted. However, the lamp
21
includes not only an essential light-emitting region but also a region which does not emit light such as electrode portion
21
a
, wherein the latter affects the display portion of the backlight (wherein the electrode portion
21
a
is illustrated to be drawn outside of the frame
26
for ease of understanding in FIG.
7
), so that irregularities in brightness X are generated in proximities of both ends of the lamp
21
at which luminous energy is decreased. If it should be possible to effectively eliminate such irregularities in brightness X, the length of the lamp
21
can be shortened up to a dimension of the display portion. In other words, the outer diametric dimension of the backlight can be reduced which is an extremely important technique for achieving narrow framing.
A conventional method which is taken for eliminating irregularities in brightness X is a method for increasing the scattering portion
25
formed on the rear surface
23
c
of the light-conducting plate
23
of FIG.
6
through printing. However, light-conducting plates are becoming popular in these years which are of a type with no scattering portion
25
being formed on the rear surface
23
c
of the light-conducting plate
23
through printing.
As a method for eliminating irregularities in brightness X without printing, there is disclosed a technique wherein the light-incident surface of the light-conducting plate is formed as a coarse surface for increasing the amount of scattered light in approaching both lateral ends of the light-incident surface (see Japanese Unexamined Patent Publication No. 160036/1997); however, employing this technique requires an additional process of forming the coarse surface using sandpapers or the like after injection molding of the light-conducting plate.
The present invention has been made in view of the above problems, and provides a sheet-like light source device capable of effectively eliminating irregularities in brightness X without performing printing and capable of being easily manufactured.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a sheet-like light source device of side-light type comprising a light-conducting plate made of a light-transmitting material, at least one rod-like light source disposed proximate to a light-incident surface comprising at least one lateral side end portion of the light-conducting plate, a tubular reflecting member covering portions other than a surface facing the light-conducting plate of the rod-like light source, and a planar reflecting member disposed proximate to a position facing a rear surface of the light-conducting plate,
wherein sloped surfaces which are inclined with respect to the light-incident surface of the light-conducting plate are formed proximate to positions of the light-incident surface of the light-conducting plate at which a luminous energy of the rod-like light source is decreased.
It is preferable that the sloped surface is inclined with respect to the light-incident surface at an angle of not less than 6°.
It is preferable that the sloped surface increases in width in approaching the positions at which the luminous energy of the rod-like light source is relatively decreased.
It is preferable that angles formed by the sloped surface and the light-incident surface of the light-conducting plate increase in approaching the positions at which the luminous energy of the rod-like light source is relatively decreased.
It is preferable that the positions at which the luminous energy of the rod-like light source is decreased are positions at which the electrode portions on both ends of the rod-like light source are located.
It is preferable that the sloped surface is formed on a front surface side and/or rear surface side of the light-incident surface of the light-conducting plate.
REFERENCES:
patent: 5961197 (1999-10-01), Watai et al.
patent: 5986727 (1999-11-01), Fukui et al.
patent: 5997148 (1999-12-01), Ohkawa
patent: 6199994 (2001-03-01), Watai
patent: 6217184 (2001-04-01), Koike et al.
Advanced Display Inc.
Choi Jacob Y.
O'Shea Sandra
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Light incident surface with sloped surfaces does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light incident surface with sloped surfaces, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light incident surface with sloped surfaces will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2977074