Illumination – Revolving
Reexamination Certificate
1999-12-14
2002-07-02
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S027000, C362S026000, C349S062000, C349S065000
Reexamination Certificate
active
06412969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a backlighting device and a method of manufacturing the same. More specifically, the present invention relates to an edgelight type backlighting device suitably used for a liquid crystal display apparatus and the like, and also relates to a liquid crystal display apparatus including the backlighting device.
2. Description of the Related Art
A class of backlighting devices for liquid crystal display apparatuses is generally known in which light generated from a capillary-like light source element (e.g., a cold cathode tube) disposed along a side face of a light guide unit enters into the light guide unit so as to be emitted through one face of the light guide unit. In such a backlighting device, the light source element and the light guide unit do not vertically overlay each other, enabling reduction of the size of the backlighting device along the thickness direction. In such a backlighting device, however, a space for disposing the light source element is required outside the light guide unit, which may become a dead space, i.e., a space which cannot be utilized as an effective viewing area, in a liquid crystal display apparatus incorporating such a backlighting device. Currently, there is an increasing need for an enlarged display area and a reduced module size, especially in on-vehicle liquid crystal display apparatuses and liquid crystal display apparatuses for mobile terminals.
Japanese Laid-open Publication No. 9-5742 discloses a relatively compact backlighting device having a structure shown in FIG.
12
. The liquid crystal display apparatus
100
shown in
FIG. 12
includes a liquid crystal panel
110
, and a backlighting device
120
disposed under the liquid crystal panel
110
. The backlighting device
120
includes a housing
122
for a light source element L, in the form of a notch provided in portion of each lateral end
121
a
of a light guide unit
121
. The light source element L is disposed within the housing
122
. A casing
123
covers the side faces and the bottom face of the light guide unit
121
. A light diffusion panel
124
and a prism sheet
125
are provided between the upper face of the light guide unit
121
and the liquid crystal panel
110
.
In the conventional backlighting device
120
, the light guide unit
121
is composed of a transparent resin and includes a narrow portion
126
at each lateral edge
121
a
where the light guide unit
121
meets the upper face of the housing
122
for light source element. The narrow portion
126
is provided by mixing a particulate material that has a different refractive index into the transparent resin. Between the narrow portion
126
and the housing
122
for light source element, a light amount adjusting filter means
127
is formed. The disclosure of Japanese Laid-open Publication No. 9-5742 teaches that both the luminance unevenness and the color irregularity of the backlighting device
120
were eliminated by providing the light amount adjusting filter means
127
on the narrow portion
126
of the light guide unit
121
.
As the light amount adjusting filter means
127
, the following structures (1)-(4) are disclosed.
(1) a reflective PET film (thickness 188 microns), having apertures with diameters of 0.2 mm or less directly formed therein, where the aperture ratio is 12%.
(2) a reflective PET film (thickness 75 microns), with white ink dots being printed exclusively in a portion immediately above the light source element.
(3) a transmissive PET film with a thickness of 100 microns, bearing a dotted layer of aluminum deposited on one side thereof, where the aperture ratio is about 12%.
(4) a transmissive PET film with a thickness of 100 microns, bearing a dotted layer of aluminum deposited on both sides thereof, where the aperture ratio is about 10%.
If dot printing is used in the above-mentioned method disclosed in Japanese Laid-open Publication No. 9-5742, however, for example, problems may occur during the production of the backlighting device, such as unwanted variation in luminance and color caused by uneven printing and irregular ink distribution due to the abrasion of the silk screen (currently, a silk screen must be replaced after having been used for ten thousand shots). On the other hand, if aluminum layer deposition is used, there are problems such as changes in the dot shape caused by degradation of the deposition mask, chromaticity shifting due to the oxidation of the deposited aluminum layer, and peeling of layers due to insufficient adhesion to the PET sheet.
Furthermore, for producing the light amount adjusting filter means
127
, some cost is incurred for, e.g., a dot printing machine, a vacuum deposition machine, and deposition jigs. Also, substantial cost is incurred that is associated with the abrasion of the machines and product inspection. Furthermore, the provision of the light amount adjusting filter means
127
on the narrow portion
126
of the light guide unit
121
may present serious cost problems associated with the cost for assembling, the cost for defects during the assembling due to defective parts or improper assembling, and the inspection cost.
Japanese Laid-open Publication No. 8-166513 discloses a light guide unit
130
as shown in
FIG. 13A. A
transmission adjusting section
131
is provided on the inner surface
130
b
of an extension
130
a
of the light guide unit
130
for adjusting the light transmittance. The transmission adjusting section
131
also has a light diffusion function. Japanese Laid-open Publication No. 8-166513 explains that linear advancement of the light from the light source element L and into the transmission adjusting section
131
is ensured because the inner surface
130
b
of the extension
130
a
of the light guide unit
130
, which faces the light source element L, curves in accordance with the curve of the emission surface of the light source element L in the vicinity where the extension
130
a
merges into the rest of the light guide unit
130
.
In accordance with the light guide unit
130
described in Japanese Laid-open Publication No. 8-166513 (see FIG.
13
A), however, the light emitted from the light source element L creates light rays which are scattered over a wide range of angles within the light guide unit
130
at the curved portion of the transmission adjusting section
131
, which is formed of white plastic. Therefore, in accordance with the light guide unit
130
, as shown in
FIG. 14
, some of the light rays which have been scattered by the curved portion of the transmission adjusting section
131
and reached the upper face of the light guide unit
130
may have an acute incident angle with respect to the upper face of the light guide unit
130
.
The critical incident angle (&thgr;
a
) is obtained from the following formula according to Shell's law:
&thgr;
a
=sin
−1
n
D
.
Assuming that the refractive index n of the air is 1.0, and the refractive index n
D
of the light guide unit
130
is 1.5, the critical angle (&thgr;
a
) is calculated to be about 42 degrees from the above formula. In this case, those light rays which strike the upper face of the light guide unit
130
with an incident angle larger than about 42 degrees are all reflected at the upper face of the light guide unit
130
back into the light guide unit
130
. On the other hand, among those light rays with incident angles smaller than the critical angle (&thgr;
a
), some are reflected at the upper face of the light guide unit
130
back into the light guide unit
130
, while others may proceed straight through, or be refracted at, the upper face of the light guide unit
130
. The light rays which have thus gone directly out of the light guide unit
130
create bright lines
132
. Due to these bright lines
132
, a different amount and/or direction of light may be obtained in regions of the upper face of the light guide unit
130
adjacent to the curved portion of the transmission adjusting section
131
, as compared to the other regions of th
Takahashi Nobuyuki
Torihara Hiroshi
Ukai Kenichi
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Truong Bao
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