Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-02-17
2003-01-07
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S065000
Reexamination Certificate
active
06504589
ABSTRACT:
This application claims the benefit of Japanese Patent Application No. 09-48563, filed in Japan on Feb. 18, 1997, and No. 09-215464, filed in Japan on Jul. 28, 1997, both of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a backlight device and, more particularly, to a backlight device for use in liquid crystal display devices and the like.
2. Discussion of the Related Art
Recently, liquid crystal display (LCD) devices having a backlight system are becoming increasingly popular. The LCD devices modulate polarized light obtained by transmitting light through a polarizing plate through a liquid crystal layer.
FIG. 11
shows the typical structure of a conventional backlight system and an LCD device. Light emitted from light source
21
is incident on light guide
22
and propagates by undergoing multiple total internal reflections. A portion of the light traveling through the light guide
22
is diffused by light diffusers
23
and is emitted from the light guide. A portion of the light emitted downward from the light guide
22
is reflected by reflection sheet
24
and returned to the interior of the light guide
22
. The light emitted upward from the light guide
22
is diffused by diffusion sheet
25
, and is converged by prism sheet (or lens sheet)
26
to enter liquid crystal cell
30
interposed between polarizing plates
31
and
32
.
FIGS. 12 and 13
show other types of conventional LCD devices having a backlight system.
The backlight device of
FIG. 12
is structured such that the order of diffusion sheet
25
and prism sheet
26
is reversed from that of FIG.
11
and the prism surface of the prism sheet is facing the light guide
22
.
The backlight of
FIG. 13
is structured such that an additional prism sheet
26
a
, which has a plurality of triangular column prisms arranged in a direction perpendicular to the arrangement direction of the triangular column prisms in prism sheet
26
, is placed over the prism the sheet
26
.
However, currently used light polarizing plates absorb approximately half of the incident light, and thus have low efficiency in light usage. That is, in order to have sufficient luminance, more light needs be incident on the light polarizing plate. However, increasing the light intensity of the light source causes a variety of problems, such as increased power consumption of the light source and adverse effects on the liquid crystal due to heat generated from the light source, which degrade the display quality.
To solve these problems, the following techniques have been proposed. A polarization light splitter is provided for splitting unpolarized light from a light source into two linearly polarized light beams having the polarization directions orthogonal to each other. One of the split polarized light beams is directly used for illumination while the other polarized light beam is used indirectly. In other words, these techniques improve light usage efficiency such that, of the two linear polarization components of light, one component is incident on the liquid crystal cell, and the other component is reflected by the polarization light splitter, returned to the light source side, and is reflected again to reintroduce it to the polarization light splitter. Some of the recent developments along this direction are as follows.
(1) In Japanese Laid-Open Patent Application No. 04-184429, an unpolarized light beam from a light source is split by a polarization light splitter into two linearly polarized light beams having polarization directions orthogonal to each other. One of the polarized light beams is emitted directly towards the liquid crystal cell. The other is returned to the light source side, converged, and then is reflected for re-use as light for illuminating the liquid crystal cell.
(2) A backlight system disclosed in Japanese Laid-Open Patent Application No. 06-265892 has a beam deflector disposed over a planar light guide to direct light emitted from the planar light in a direction approximately perpendicular to the surface of the planar light guide. A polarization light splitter is located over the beam deflector.
(3) A backlight system disclosed in Japanese Laid-Open Patent Application No. 07-261122 has a polarization light splitter located on the light emitting surface side of a parallel light generating device, which is constructed of a light scattering guide that includes a portion having a wedge-shaped profile.
However, these conventional technologies have the following problems. The backlight system of (1) is intended for use with a projection LCD device. Since the structure of the illumination device requires a large amount of space, it cannot be applied for a planar thin LCD device.
The backlight system of (2) is suitable for constructing thin devices. With a polarization light splitter layer fabricated on the inclined sides of a columnar prism array having a plurality of triangular shaped elements, superior efficiency in light usage can be obtained. However, the structure of the polarization light splitter is complicated and, in particular, it is difficult to form the polarization light splitter layer on the inclined sides of the triangular shaped elements. Therefore, the device is not suitable for mass production.
In the technology (3), if the parallel light generating device of the light guide is constructed of a finely designed light scattering guide that includes a portion having a wedge-shaped profile, superior efficiency in light usage can be obtained. However, it is difficult to design and manufacture such a light scattering guide having the desired function. Therefore, this device is not convenient for general use.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a backlight device that substantially obviates the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a backlight device that has a polarized light splitting film with a relatively simple, thin structure suitable for mass production and that has high efficiency in light usage.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the backlight device of the present invention includes a light source; a light guide for receiving light from the light source at one end and for emitting directional light that has its maximum strength in a first predetermined direction; a polarization light splitter having a planar multi-layer structure; and a beam deflector disposed between the light guide and the polarization light splitter for deflecting the directional light from the light guide light towards the polarization light splitter in a second predetermined direction along which the polarization light splitter has its maximum polarized light splitting effect. As a result, the light usage efficiency from the light source can be improved. In addition, the polarization light splitter of the present invention has a planar shape suitable for manufacturing thin, compact backlight systems and LCD devices.
It is desirable to use a light guide having a plate-like shape. Light diffusing means may be provided in the light guide. Light diffusing means for the light guide may include a light diffusing layer that is in optical contact with the emitting surface of the light guide or formed by roughening the emitting surface or the opposite surface of the light guide. A light guide having light scattering (diffusing) property by itself may also be used as the light diffusing means. In addition, it is desirable that the light deflector be a
Arakawa Fumihiro
Kashima Keiji
Dai Nippon Printing Co. Ltd.
Morgan & Lewis & Bockius, LLP
Parker Kenneth
LandOfFree
Backlight device and 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 and liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Backlight device and liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052204