Illumination – Revolving
Reexamination Certificate
2002-07-22
2004-11-02
Husar, Stephen (Department: 2875)
Illumination
Revolving
C362S027000
Reexamination Certificate
active
06811275
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display.
2. Description of the Related Art
A liquid crystal display characterized by its small occupied volume, low-profile and light-weight has been extensively used in electric products including cellular phones and personal computers and the demand thereof has been increasing. However, since a liquid crystal of the liquid crystal display (hereinafter, referred to as “LCD”) does not emit light by itself, a separate illuminating means for irradiating the LCD is needed besides the LCD when used in dark places where sunlight or room light is not satisfactorily available. Thus, this illuminating means is required not only to be small in size and in power consumption, but also to project high quality images on an observation surface. In particular in recent years, a sheet-like spread illuminating apparatus of side light type (light conductive plate type) is often applied as an illuminating means.
FIG. 5
shows an embodiment of a conventional spread illuminating apparatus of side light type, which aimed for a uniform spread light emission (disclosed in the Japanese Unexamined Patent Application Publication No. 2000-11723) described hereinafter.
A spread illuminating apparatus
1
′ disposed over an upper surface of a reflection type liquid crystal element L is generally composed of a flat rectangular light conductive plate
2
made of a light-transmissible material, a lamp
4
disposed close to a side surface
3
thereof, and a light reflection member
12
(a reflector) covering the lamp
4
and two edges of top and bottom surfaces of one end of the light conductive plate
2
.
The lamp
4
is composed of a light conductive bar
7
and light sources (shaped spot-like)
9
and
9
such as light emitting diodes disposed at both end surfaces
8
and
8
of the light conductive bar
7
. An optical path conversion means
11
including grooves
15
substantially triangular in section and flat portions
16
formed therebetween is formed on a side surface
14
opposite to a surface
13
facing the side surface
3
of the light conductive plate
2
. Light traveling inside the light conductive bar
7
tends to be reflected mostly by means of each inclined surface forming each of the grooves
15
so as to advance in the direction substantially perpendicular to the surface
13
. Comparing with the flat portions
16
, the grooves
15
reflect more amount of light entering the light conductive plate
2
after passing through the side surface
13
. Thus, the ratio of the width of each of the grooves
15
to the width of each of the flat portions
16
is set to be proportional to the distance from each of the ends
8
of the light conductive bar
7
. Since the width of each of the grooves
15
in the optical path conversion means
11
is formed in consideration of the distance from the light source
9
, the uniform emission of light from the surface
13
can be realized regardless of the fact that the light sources are each disposed at each of the end surfaces
8
,
8
of the light conductive bar
7
.
In this connection, the configuration of the optical path conversion means
11
is not limited to the above embodiment, and the optical path conversion means
11
may comprise light scattering portions with minute ruggedness formed by roughening the surface thereof and flat portions without ruggedness.
A light reflection pattern
17
is formed on an upper surface
6
of the light conductive plate
2
in parallel to the side surface
3
. The light reflection pattern
17
comprises a plurality of grooves
18
each substantially triangular in section and flat portions
19
adjacent thereto, and the grooves
18
is spaced unevenly in order to realize the uniform spread light emission of the light conductive plate
2
irrespective of the distance from the lamp
4
. This means that the ratio of the width (occupied area) of each of the grooves
18
to the width (occupied area) of each of the flat portions
19
is set to be proportional to the distance from the end surface
3
of the light conductive plate
2
.
The light reflection member
12
covers longitudinal surfaces of the light conductive bar
7
except the surface
13
facing the light conductive plate
2
, and also covers two edges of upper and lower surfaces of the one end of the light conductive plate
2
which is close to the light conductive bar
7
in order to recover light leaking out of the conductive bar
7
and to make an efficient utilization of the light traveling within the light conductive bar
7
. The light reflection member
12
formed substantially U-shaped has, on its surfaces covering the light conductive bar
7
(inner surfaces), any one of a film on which a metal such as silver is vapor-deposited, a hard resin with a white film adhered to its inner surface, and a bent metal sheet such as a bent aluminum sheet, and a bent stainless steel sheet.
However, in the spread illuminating apparatus with the above configuration, there is a shortcoming that light-and-dark stripes are generated in the direction orthogonal to the side surface
3
of the light conductive plate
2
when observing the screen, which is due to the optical path conversion means
11
formed on the light conductive bar
7
. That is, most of light reflected by the light scattering portions
15
of the optical path conversion means
11
enters the light conductive plate
2
after being emitted from the side surface
13
, whereas most of light reflected by the flat portions
16
is totally reflected and travels within the light conductive bar
7
without being emitted from the side surface
13
. Accordingly, it is, in a strict sense, impossible to make a luminous intensity at the side surface
13
become uniform due to the above design pattern comprising the light scattering portions
15
and the flat portions
16
. As a result, the lightness of the light entering the light conductive plate
2
becomes non-uniform, and the light-and-dark stripes orthogonal to the end surface
3
are generated on the observational screen. One of the countermeasures therefor is to make the light scattering portions
15
and the flat portions
16
more minute to the level that the light-and-dark stripes can not be visually recognized. However, it is difficult to obtain a desired machining accuracy by employing this method.
Another countermeasure therefor is that, as shown in
FIG. 6
, a diffusion plate
20
is interposed between the light conductive bar
7
and the light conductive plate
2
so as to make uniform the luminance of the light entering the light conductive plate
2
. In the diffusion plate
20
a light diffusion unit containing a light diffusive substance is formed on a plate-like supporting base. The light emitted from the side surface
13
of the light conductive bar
7
is diffused when passing through the diffusion plate
20
so that the luminance of the light entering the side surface
3
of the light conductive plate
2
can be made substantially uniform (disclosed in the Japanese Unexamined Patent Application Publication No. 2000-231814).
A spread illuminating apparatus
1
″ with the diffusion plate
20
shown in
FIG. 6
is effective for making the luminous intensity uniform on an observation surface. However, the light emitted from the side surface
13
and diffused during passing through the diffusion plate
20
has a lower light transmissivity for entering the side surface
3
of the light conductive plate
2
, so that more power consumption is needed to obtain the predetermined luminance on the observation screen. Moreover, due to the complicated manufacturing steps, the working efficiency will be accordingly decreased.
In addition, even if the optical path conversion means is spaced as narrowly as possible in the hope of obtaining the desired machining accuracy without using any diffusion plate, it is almost impossible to prevent the
Kunimochi Toru
Suzuki Shingo
Cranson James W
Husar Stephen
Minebea Co. Ltd.
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