Illumination – Light fiber – rod – or pipe – Diffuser or diffusing of incident light
Reexamination Certificate
2002-03-22
2004-03-30
O'Shea, Sandra (Department: 2875)
Illumination
Light fiber, rod, or pipe
Diffuser or diffusing of incident light
C362S551000, C362S035000
Reexamination Certificate
active
06712492
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illuminating means for signboards, various kinds of reflection-type display devices and the like, and more particularly for a liquid crystal display.
2. Description of the Related Art
A liquid crystal display as a display for many electric products such as cellular phones and personal computers has been increasingly demanded due to its low profile, small occupied volume, and light weight. Since the liquid crystal display uses a liquid crystal, which does not emit light by itself, an illuminating apparatus is required when used in dark places where sufficient sunlight or room illumination is unavailable. Thus, the illuminating apparatus to illuminate the liquid crystal is desired to be compact and small in power consumption, and at the same time, high image quality is desired on the observation surface. Accordingly, there has been a growing tendency to employ a thin plate-like spread illuminating apparatus of side light type (light conductive plate type) as an illuminating means for the liquid crystal display.
FIG. 12
shows an example of a conventional side light type spread illuminating apparatus. This spread illuminating apparatus has been devised to realize a uniform spread light emission (Japanese Patent Laid-open No. 2000-11723), and the detail thereof is described below.
A spread illuminating apparatus
1
′ is disposed so as to cover an upper face of a reflection-type liquid crystal element L, and is generally composed of a plate-like transparent substrate
2
shaped rectangular in section and made of a light-transmissible material, a light source
4
disposed close to one end face
3
of the transparent substrate
2
, and a light reflection member (reflector)
12
to cover the light source
4
and a portion of the transparent substrate
2
near the one end face
3
.
The light source
4
is composed of a bar-like light conductive member
7
, and spot-like light sources
9
and
9
′ such as light-emitting diodes disposed on both ends
8
of the light conductive member
7
. An optical path conversion means
11
is formed on one face
14
of the light conductive member
7
opposite to a face
13
facing the end face
3
of the transparent substrate
2
, and is composed of grooves
15
as light scattering portions shaped, for example, triangular in section, and flat portions
16
adjacent to the grooves
15
. The interval of the grooves
15
is set to gradually decrease with the increase in distance from the spot-like light sources
9
and
9
′. Thus, the optical path conversion means
11
is formed in consideration of a balance between the distance from respective spot-like light sources
9
and
9
′ and the interval of the grooves
15
, whereby light is uniformly emitted through the face
13
of the light conductive member
7
despite the spot-like light sources
9
and
9
′ being disposed on the ends
8
of the light conductive member
7
. The optical path conversion means
11
is not limited to the above configuration but may comprise grooves without flat portions or comprise light scattering portions with a finely roughened surface and plain portions with a smooth surface.
A light reflection pattern
17
is formed on an upper face
6
of the transparent substrate
2
in parallel to the end face
3
. The light reflection pattern
17
is composed of a large number of grooves
18
substantially triangular in section and flat portions
19
adjacent to the grooves
18
, and the interval between adjacent grooves
18
is varied from position to position so as to make the illumination uniformly spread everywhere on the transparent substrate
2
irrespective of the distance from the light source
4
. Specifically, the ratio of the width (occupied area) of the grooves
18
to the width (occupied area) of the flat portions
19
is set to gradually increase in proportion to the increase in distance from the end face
3
of the transparent substrate
2
.
Further, a light reflection member
12
is disposed so as to cover the longitudinal faces of the light conductive member
7
except the face
13
and the end of the transparent substrate
2
close to the light conductive member
7
, whereby light emitted from the spot-like light sources
9
and
9
′ into the light conductive member
7
is efficiently guided into the transparent substrate
2
. The light reflection member
12
is made of a hard resin product substantially U-shaped in section, and having a metal (such as silver) vapor deposited film, a white film, etc. stuck on its inner surface, or made of a U-shape bent metal sheet such as an aluminum sheet and a stainless steel sheet, and disposed so as to cover the light conductive member
7
.
However, the above spread illuminating apparatus has a disadvantage that dark and bright fringes orthogonal to the end face
3
appear on the screen. The dark and bright fringes are attributable to the optical path conversion means
11
formed on the light conductive member
7
, which means that while light reflected at the grooves
15
of the optical path conversion means
11
is mostly emitted through the face
13
to be guided into the transparent substrate
2
, light reflected at the flat portions
16
mostly undergoes total reflection and is not emitted through the face
13
, and thus, the light is emitted through the face
13
with uneven brightness according to the pattern of grooves
15
and the flat portions
16
. Since the brightness of light guided into the transparent substrate
2
is uneven, dark and bright fringes orthogonal to the end face
3
are generated on the screen. This problem can be solved if the pattern of the grooves
15
and the flat portions
16
is finely structured but it is difficult to ensure a machining accuracy required to realize such a fine structure.
So, it was proposed that a light diffusion plate
20
be disposed between the light conductive member
7
and the transparent substrate
2
as illustrated in
FIG. 13
so as to uniform the brightness of light incident on the transparent substrate
2
. The light diffusion plate
20
is structured such that a light diffusion portion containing a light diffusion substance is formed on a thin plate, and diffuses light emitted through the face
13
of the light conductive member
7
to substantially uniform the brightness of light incident on the end face
3
of the transparent substrate
2
(Japanese Patent Laid-open No. 2000-231814).
A spread illuminating apparatus
1
″ shown in
FIG. 13
is effective in uniforming the brightness of light on an observation surface but has a disadvantage that the transmittance of the light diffusion plate
20
is low, which degrades the ratio of utilization of light from the light source
4
resulting in an increased power consumption to obtain a required brightness on the screen.
However, without the light diffusion plate, the spread illuminating apparatus still suffers the problem that the dark and bright fringes cannot be fully eliminated on the screen even when the optical path conversion means is structured finely with highest machining accuracy.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above, and an object of the present invention is therefore to provide a spread illuminating apparatus which can ensure uniform and high brightness entirely over the screen without increasing power consumption.
In order to solve the above problems, according to a first aspect of the present invention, there is provided a Spread illuminating apparatus which comprises a transparent substrate made of a light-transmissible material and a light source composed of a bar-like light conductive member and at least one spot-like light source disposed on an end of the light conductive member, disposed along and close to an end face of the transparent substrate, and having an optical path conversion means which comprises a large number of light scattering portions, such as grooves, with or without flat
Nakamura Yoshiki
Shimura Takahiro
Toyoda Koichi
Minebea Co. Ltd.
O'Shea Sandra
Oliff & Berridg,e PLC
Truong Bao Q.
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