Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-06-07
2003-08-26
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S064000
Reexamination Certificate
active
06611303
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a backlight device for use in the LCD device.
2. Description of Related Art
FIG. 1
shows a conventional backlight device for use in a LCD device. As shown in
FIG. 1
, the conventional backlight device
1
comprises a light source
10
, a U-shaped lamp holder having a lamp reflector
16
, and a light waveguide plate
40
. The light source
10
is located adjacent to an end
40
a
of the light waveguide plate
40
, and most of the light source
10
is surrounded by the lamp holder
15
. The end
40
a
constitutes a surface through which the incident light from the light source
10
is emitted.
The emitted light from the light source
10
is directed toward the surface
40
a
of the light waveguide plate
40
by the lamp reflector
16
. The light waveguide plate
40
directs light either toward a prism sheet
20
or a reflector
50
. The light reflected by the reflector
50
is emitted toward the observer through a prism sheet
20
, a diffusing sheet
30
and a liquid crystal panel (not shown) in the form of an information.
The aforementioned backlight device is disclosed in the prior art, for example, the Japanese Patent Publication of Application No. 6-118246. The prior art prism sheet
20
has a plurality of convex portions
33
for collecting the light emitted from the light waveguide plate
40
. The convex portions
33
of the prism sheet
20
can have a fan shape (FIG.
1
), a regular triangle shape (
FIG. 2
a
), an isosceles triangle shape (
FIG. 2
b
), or a half-circle shape (
FIG. 2
c
). Therefore, the prism sheet
20
having a plurality of the convex portions
33
collects the light emitted from the light waveguide plate
40
not to be scattered so that the regularly directional light is emitted toward the diffusing sheet
30
.
However, even though the prism sheet
20
having a plurality of the convex portions
33
is arranged, light loss may occur. For example, as shown in
FIG. 2
a
, part of the emitted light from the light waveguide plate
40
is total-reflected only to be directed downwardly, and then the light reflected on the reflector
50
again is directed upwardly, having a large refraction angle with respect to the vertical direction.
Further, if the prism sheet is used together with a cholesteric liquid crystal; (CLC) polarizer, the color change property and light efficiency may decrease. In general, a directional vector of a CLC layer has a helical structure. When a right-handed circularly polarized lightis incident to the CLC layer having a-left-handed helical structure, the CLC layer reflects only a light having a wavelength that satisfies a Bragg reflection condition. Using such a principle, the CLC polarizer can use even light lost in an absorbing type polarizer, thereby remarkably improving light efficiency. In the same way, when a CLC color filter is used, the light efficiency is much improved.
However, when an incident angle of the circularly polarized light is greater than 20 degrees, the transmitted light is produced in the form of not circularly polarized light, but eliptically polarized light. Besides, a wavelength of the transmitted light is different from that of the incident light, thereby lessening the color change property and the light efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a backlight device for a liquid crystal display device such that the light collecting efficiency and light illumination are much improved.
In order to achieve the above object, the present invention provides a backlight device for a liquid crystal display device, which includes a light source; a light waveguide plate having an end portion and a front portion; a lamp holder having a lamp reflector, the lamp holder surrounding most part of the light source, the lamp reflector reflecting light to the end portion of the light waveguide plate; and a first prism sheet located on the front portion of the light waveguide plate, the prism sheet having a plurality of convex portions, the convex portions having an inclined line portion and a curved line portion, the inclined line portion having a predetermined angle with respect to a direction vertical to the front portion of the light waveguide plate.
The angle of the inclined line portion is less than 20°. The light waveguide plate has a plurality of convex or concave hole dots. The light waveguide plate has a plurality of V-shaped convex or concave bars.
The backlight device further includes a reflector, arranged under the light waveguide plate and a diffusing sheet, interposed between the light waveguide plate and the first prism sheet; a second prism sheet having a plurality of convex portions, the second prism sheet arranged on the first prism sheet; a cholesteric liquid crystal polarizer arranged on the second prism sheet; and a quarter wave plate arranged on the cholesteric liquid crystal polarizer.
REFERENCES:
patent: 586247 (1897-07-01), Soper
patent: 720386 (1903-02-01), Wadsworth
patent: 720987 (1903-02-01), Wasworth
patent: 5418631 (1995-05-01), Tedesco
patent: 5961198 (1999-10-01), Hira et al.
patent: 6011601 (2000-01-01), Kojima
patent: 6011602 (2000-01-01), Miyashita et al.
patent: 6023316 (2000-02-01), Yano
patent: 6079841 (2000-06-01), Suzuki
patent: 6104455 (2000-08-01), Kashima
patent: 6130730 (2000-10-01), Jannson et al.
patent: 6196691 (2001-03-01), Ochiai
patent: 6215936 (2001-04-01), Yoshikawa et al.
patent: 6356391 (2002-03-01), Gardiner et al.
patent: 6118246 (1994-04-01), None
patent: 06331981 (1994-12-01), None
English language Abstract of JP 6-118246.
Lee Jong-hoon
Lee Seehyung
Park Chul
Birch & Stewart Kolasch & Birch, LLP
Kim Robert H.
LG. Philips LCD Co. LTD
Nguyen Dung
LandOfFree
Backlight device for a liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Backlight device for a liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Backlight device for a liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3090215