Illumination – Revolving
Reexamination Certificate
2002-08-26
2004-06-15
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S331000, C362S326000, C362S027000
Reexamination Certificate
active
06749311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display (hereinafter, referred to as “LCD”) featuring low power consumption, low profile and light weight has been extensively used in electric products including cellular phones and personal computers.
However, since a liquid crystal, which is a structural element of the LCD, does not emit light by it self unlike a light emitting element such as a CRT, the LCD requires a separate illuminating means in order to observe an image. Recently, to satisfy the demand for downsizing and energy saving, a sheet-like spread illuminating apparatus of side light type (light conductive plate type) is often used.
An example of a spread illuminating apparatus of side light type is shown in FIG.
9
.
In
FIG. 9
, a spread illuminating apparatus
1
is generally constituted such that a lamp
4
is disposed along and close to an end surface
3
of a light conductive plate
2
made of a light-transmissible material. The light conductive plate
2
is shaped rectangular and has a light reflection pattern
5
formed on a major surface thereof.
The lamp
4
is generally composed of a light conductive bar
6
shaped like a slim-rectangular-prism, made of a transparent material and arranged with a surface
6
a
along and close to the end surface
3
of the light conductive plate
2
, and a spot-like light source
7
arranged to face an end surface of the light conductive bar
6
.
The light conductive bar
6
has an optical path conversion means
8
formed on a side surface
6
b
thereof opposite to the side surface
6
a
facing the end surface
3
of the light conductive plate
2
. The optical path conversion means
8
comprises a plurality of grooves
9
, for example, triangular in section, extending in a direction of thickness of the light conductive bar
6
, and arrayed in a longitudinal direction of the light conductive bar
6
(hereinafter, referred to as “stair-like type”) and makes light emitted from the spot-like light source
7
incident in a substantially uniform manner on the end surface
3
of the light conductive plate
2
. In order to make the light to uniform, the triangular grooves
9
have their depths gradually increased in proportion to an increase in the distance from the spot-like light source
7
.
Also, the spread illuminating apparatus
1
includes a frame
10
substantially U-shaped in section, having a predetermined width L1 and having a light reflection member (not shown) on its inner surface, and covers longitudinal surfaces of the light conductive bar
6
except the side surface
6
a
facing the light conductive plate
2
, and an end portion (two surfaces toward the end surface
3
of the light conductive plate
2
), thereby recovering light leaking from the light conductive bar
6
to improve the usability of the light.
The frame
10
is adapted also to securely hold together the light conductive bar
6
and the light conductive plate
2
with a predetermined strength.
Recently, the above-described spread illuminating apparatus is strongly demanded to have as large a liquid crystal screen area as possible. Accordingly, the frame is requested to have its portion minimized which covers the liquid crystal screen, and to meet this request in a compact configuration.
In the prior art shown in
FIG. 9
, if the width L1 of the frame
10
is decreased to comply with the above request, the covered area at the light conductive plate
2
is reduced making it difficult to securely hold together the light conductive bar
6
and the light conductive plate
2
.
Under the circumstances, the present applicants have proposed a spread illuminating apparatus in Japanese Patent Application 2001-8966, in which the covered portion over the liquid crystal screen is minimized and the light conductive bar and the light conductive plate are strongly held together, while miniaturization is achieved. A spread illuminating apparatus
1
A proposed in the above application includes a light conductive bar
20
and a light conductive plate
21
as shown in FIG.
10
. The light conductive bar
20
is wedge-shaped and has a larger end surface
20
a
facing a spot-like light source
7
. The light conductive plate
21
has an inclination angle (inclination angle on a light conductive plate) &bgr;, which is an obtuse angle formed between an end surface
21
of the light conductive plate
21
a
facing the light conductive bar
20
and a side surface
21
b
thereof flush with the end surface
20
a
facing the spot-like light source
7
. The light conductive bar
20
has an inclination angle (inclination angle of the light conductive bar) &agr;, which is an acute angle formed between a side surface
20
b
of the light conductive bar
20
facing the light conductive plate
21
and the surface
20
a
facing the spot-like light source
7
.
In the apparatus shown in
FIG. 10
, when the light conductive plate
21
and the light conductive bar
20
are held together by the frame
10
(see FIG.
9
), since the light conductive bar
20
is wedge-shaped, the frame
10
has a sufficiently large area to cover the light conductive plate
21
toward an end surface
20
c
of the light conductive bar
20
opposite to the end surface
20
a
facing the spot-like light source
7
. Therefore, even when the width of the frame
10
is decreased, the frame
10
retains a sufficient strength to hold together the light conductive bar
20
and the light conductive plate
21
, whereby the apparatus can be successfully downsized with an increased liquid crystal screen.
The optical path conversion means formed on the light conductive bar may comprise a plurality of grooves
20
e
and a plurality of flat portions
20
f
each connecting adjacent grooves
20
e
as shown in
FIG. 11
rather than the stair-like type shown in FIG.
10
.
However, in the prior art shown in
FIGS. 9
to
11
, the side surface
20
b
of the light conductive bar
6
facing the light conductive plate
21
and a side surface
20
d
opposite to the surface
20
b
come closer to each other as approaching the end surface
20
c
which is smaller than the end surface
20
a
. Therefore, when light introduced into the light conductive bar
20
through the end surface
20
a
travels toward the end surface
20
c
while repeating reflection at the side surface
20
b
and the side surface
20
d
(flat portions
20
f
), the angle of reflection decreases at each reflection, becomes smaller than the critical angle before the light reaches the end surface
20
c
, and exits out (leakage light) from the side surface
20
b
as shown in FIG.
12
. In other words, the light introduced into the light conductive bar
20
from the surface
20
a
cannot sufficiently travel up to the end surface
20
c
, that is, the light cannot be sufficiently kept in the light conductive bar
20
, thereby decreasing the luminance of the spread illuminating apparatus. This is also the case with the light conductive bar with the optical path conversion means of stair-like type.
In this connection, the present applicants proposed a spread illuminating apparatus, in which a plurality of wedge-shaped light conductive bars are arranged in parallel along the end surface of the light conductive plate in Japanese Patent Application No. 11-232652 (Japanese Unexamined Patent Application publication No. 2001-57106).
This spread illuminating apparatus still has the same problem as the prior art shown in
FIG. 12
in that the leakage light is generated.
A spread illuminating apparatus with a wedge-shaped light conductive bar capable of forwarding light all the way up from one end surface to the other end surface thereof (keeping light therein) is disclosed in U.S. Pat. No. 5,894,539. The spread illuminating apparatus generally includes a wedge-shaped light conductive bar
20
B as shown in FIG.
13
. The light conductive bar
20
B has
Kunimochi Toru
Suzuki Shingo
Alavi Ali
Minebea Co. Ltd.
Oliff & Berridg,e PLC
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