Illumination – Revolving
Reexamination Certificate
2002-11-15
2004-07-13
Husar, Stephen (Department: 2875)
Illumination
Revolving
C349S065000
Reexamination Certificate
active
06761461
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 with a liquid crystal display.
2. Description of the Related Art
A liquid crystal display (hereinafter referred to as LCD), which is small in power consumption, low in profile, and light in weight, is heavily used in electric products such as a personal computer (hereinafter referred to as PC), a cellular phone, and the like, and is increasingly demanded.
Since a liquid crystal of the LCD does not emit light by itself, the LCD requires an illuminating means to radiate light on the liquid crystal when used in a place where sunlight or interior lighting is not fully available.
A PC, particularly notebook-type PC, and a cellular phone are required to be lower in profile and smaller in power consumption, and the requirements are fulfilled by a spread illuminating apparatus of side light type, an example of which is shown in
FIG. 10
(disclosed in Japanese Patent Application Laid-open No. 2000-11723).
In
FIG. 10
, a spread illuminating apparatus
1
is disposed over a front shoe F (upper side of the figure) of a reflection-type liquid crystal element
2
. The spread illuminating apparatus
1
comprises: a light conductive plate
3
shaped substantially rectangular and made of a light transmissible material; a light conductive bar made of a light transmissible material; and spot-like light sources
5
,
5
such as light emitting diodes (LEDs).
The light conductive plate
3
has a major surface
6
(upper aide in the figure, hereinafter referred to as “top surface”) which is an observing surface, and another major surface
7
(hereinafter referred to as “bottom surface”) which faces the reflection-type liquid crystal element
2
.
The light conductive bar
4
is disposed with its side surface
8
positioned close to or in contact with an end surface
9
of the light conductive plate
3
, and has the light sources
5
,
5
disposed on its both end surfaces
10
,
10
, respectively. The light conductive bar has an optical path conversion means
12
formed on its side surface
11
opposite to the side surface
8
facing the end surface
9
of the light conductive plate
3
. The optical path conversion means
12
comprises a plurality of grooves
13
substantially triangular in section and a plurality of flat portions
14
present between adjacent grooves
13
,
13
, and is adapted to guide light rays emitted from the light sources
5
,
5
toward the end surface
9
of the light conductive plate
3
.
The light conductive plate
3
has a light reflection pattern
15
formed on the top surface
6
. The light reflection pattern
15
comprises a plurality of grooves
16
shaped substantially triangular in section and extending parallel to the end surface
9
of the light conductive plate
3
and a plurality of flat portions present between adjacent grooves
16
,
16
, and is adapted to reflect light rays exiting out from the light conductive bar
4
toward the bottom surface
7
.
In the spread illuminating apparatus
1
thus structured, light rays emitted from the light sources
5
,
5
and introduced into the light conductive bar
4
have their optical paths changed at the optical path conversion means
12
, and travel into the light conducive plate
3
through the end surface
9
.
The light rays introduced into the light conductive plate
3
repeat reflections and reflections at the light reflection pattern
15
and other portions, progress toward an end surface opposite to the end surface
9
, and exit out in the meantime from the bottom surface
7
to illuminate the reflection-type liquid crystal element
2
disposed close to the bottom surface
7
, whereby the reflection-type liquid crystal element
2
performs emission (indirect emission) display function.
In the above described spread illuminating apparatus
1
, the light rays emitted from the light sources
5
,
5
are consumed while traveling inside the light conductive bar
4
, and have their amounts decreased. To overcome this problem, a spread illuminating apparatus was disclosed in Japanese Patent Application Laid-open No. 2001-35222.
The spread illuminating apparatus disclosed therein is shown in
FIG. 11. A
light entry face
21
is provided at a corner
18
of a light conductive plate
3
so as to be substantially orthogonal to a line
20
(hereinafter referred to as “diagonal line”) defined by connecting the corner
18
and a corner
19
diagonally opposite to the corner
18
. A spot-like light source
5
, for example an LED, is disposed close to or in contact with the light entry face
21
. A light reflection pattern
15
A is formed on a top surface of the light conductive plate
3
. The light reflection pattern
15
A comprises a plurality of arced grooves
16
A and a plurality of flat portions
17
A present between adjacent grooves
16
A,
16
A. The arced grooves
16
A correspond to partial circumferences of circles which are concentric with one another about the light source
15
and which have respective different radii. Since this spread illuminating apparatus eliminates the light conductive bar
4
used in the apparatus shown in
FIG. 10
, light rays emitted from the light source
5
are introduced immediately into the light conductive palate
8
, thereby preventing the loss of light conventionally incurred due to light traveling inside the light conductive bar
4
.
Light rays are desired to exit out from the light conductive plates
3
in a uniform manner so as to ensure excellent illumination precision. For example, in the spread illuminating apparatus
1
disclosed in the aforementioned Japanese Patent Application Laid-open No. 2000-11723 (see FIG.
10
), the grooves
16
of the light reflection pattern
15
have their depths increasing and/or have their in-between intervals decreasing with an increase in the distance from the light conductive bar
4
. With this structure, light rays are reflected at the light refection pattern
15
toward the bottom surface
17
in a larger amount at a portion farther from the light conductive bar
14
, whereby uniform emission is ensured all over the light conductive plate
3
.
This is the case with the apparatus shown in
FIG. 11
, and the arced grooves
16
A have their depths increasing and/or have their in-between intervals decreasing with an increase in the distance from the light source
5
in order to ensure uniform emission all over the light conductive plate
3
. In this case, however, as shown in
FIG. 12
, the brightness decreases from an area positioned at and near the diagonal line
20
(hereinafter referred to as “diagonal line area”) toward an area positioned circumferentially away from the diagonal line area, specifically the brightness decreases with an increase in the emission angle &phgr; made by the light direction line with respect to the diagonal line
20
. This happens because the LED as the light source
5
has a light emission characteristic shown in
FIG. 12
, where with a datum luminous intensity defined by the luminous intensity of an LED whose emission angle &phgr; of a direction along the paper surface of
FIG. 11
(X—X direction in
FIG. 12
) is 0° and whose emission angle (referred to also as “&phgr;” for the sake of convenience) of a direction orthogonal to the paper surface of
FIG. 11
(Y—Y direction in
FIG. 12
) is 0°, the ratio of the luminous intensity (relative luminosity) of the LED at a prescribed emission angle &phgr; (X—X direction or Y—Y direction) to the datum luminosity intensity is taken along the ordinate and shown as a function of the emission angle &phgr; taken along the abscissa. As shown in
FIG. 12
, the relative luminosity decreases gradually as indicated by the solid line while the emission angle &phgr; (X—X direction) increases from 0°, hence the area corresponding to a larger emission angle &phgr; has a lower luminous intensity in the spread illuminating apparatus shown in FIG.
11
.
SUMMARY OF THE INVENTION
The present invention has been made
Egawa Motoji
Mizutani Hitoshi
Suzuki Shingo
Cranson James
Husar Stephen
Minebea Co. Ltd.
Oliff & Berridg,e PLC
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