Optical: systems and elements – Diffusing of incident light
Reexamination Certificate
1997-05-27
2001-08-14
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Diffusing of incident light
C359S707000, C359S831000, C349S065000, C362S035000
Reexamination Certificate
active
06275338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a light regulation device for regulating the travelling direction of light. and more particularly to a light regulation element for regulating the travelling direction of the light emitted from a surface light source device.
2. Description of Related Art
Where a surface light source device is applied to the backlight of a liquid crystal display, a range in which the display contents of the liquid crystal display can be clearly and visually recognized, that is, a view angle, and a brightness observed when the display screen is watched are affected by the travelling direction and spread of the light emitted from the surface light source device.
The more diffused the light emitted from the surface light source device, the wider the view angle becomes, but the darker the display becomes.
On the contrary, the less diffused the emitted light, the narrower the range of view angle becomes, but the larger the quantity of the light travelling in a specific direction becomes. When the display is watched in a direction corresponding to the light travelling direction, the display is observed to be bright.
On the contrary, when the direction in which the display is watched is largely deviated from the light travelling direction, the contrast of the display is lowered to cause the display contents not to be visually recognized.
Thus, where a surface light source device is applied to the backlight of a liquid crystal display, it has been necessary to change the diffusion state and travelling direction of the light emitted from the surface light source device in such a manner that the view angle and the display required for the liquid crystal display are adapted to the watching direction.
Also, where a surface light source device is used for a local illumination for illuminating a specific area, the more diffused the light, the wider area the device can illuminate, but the lower the illuminance becomes. On the contrary, the less diffused the light, the narrow area the device illuminates, but the higher the illuminance becomes.
Of course, also for the local illumination, the regulation of the light travelling direction is important, so that the light is required not to proceed in an undesirable direction.
According a conventional a method of changing the diffusion state and travelling direction of the light emitted from a surface light source device, both a diffusion element are arranged and a light regulation element are arranged on the emission surface of a surface light source device.
FIG. 5
illustrates an example of the configuration of a conventional surface light source device. Referring to
FIG. 5
, a cylindrical light source
2
is arranged along an incident surface
1
b
of a light guide
1
. Arranged on an emission surface
1
a
of the light guide
1
are a light regulation element
3
and a diffusion element
6
in a state in which they are overlapped in a manner not to completely contact to each other. Arranged on the surface on the side opposite to the emission surface
1
a
of the light guide
1
is a reflection element
4
.
The light emitted from the light source
2
enters the light guide
1
from the incident surface
1
b
of the light guide, and part of the light while travelling in the light guide
1
is emitted directly from the emission surface
1
a
. And another part of the light is reflected by a rough surface (not shown), or an ink print portion or the like formed on the light guide
1
, and emitted form the emission surface
1
a.
The light emitted from the emission surface
1
a
penetrates the light regulation element
3
. The light travelling direction is bent by the action of many protrusions
3
a
provided on one surface of the light regulation element
3
, whereby the light travelling direction is regulated in a desirable direction. Then, the light penetrates both a very narrow gap
10
(shown exaggeratedly in
FIG. 5
) formed between the light regulation element
3
and the diffusion element
6
and then the diffusion element
6
, whereby the diffusion state of the light can be changed to a desired one.
However, for the surface light source device shown in
FIG. 5
, it is necessary to arrange both the light regulation element
3
and the diffusion element
6
on the emission surface
1
a
of the light guide.
If foreign matters such as dirt and dust adhere onto optical parts, or a flaw occurs thereon, the performance thereof will be remarkably deteriorated. Particularly for a surface light source device as shown in
FIG. 5
, there has frequently occurred a problem in that foreign matters are caught between the light regulation element
3
and the diffusion element
6
in the manufacturing process thereof.
Also where the surface light source device is assembled, individual parts must be checked to make sure there is no flaw or dirt, and then assembled with meticulous care. As a result, an increase by only one in the number of parts causes the manufacturing cost to be significantly increased.
Further, means for fixing both the light regulation element
3
and the diffusion element
6
are necessary, so that the size of the surface light source device tends to be large.
Further, a fact that the gap
10
consisting of an air layer exists between the light regulation element
3
and the diffusion element
6
generally means that, a layer having a refractive index much smaller relatively exists between the light regulation element
3
and the diffusion element
6
. Therefore, although the gap
10
has an effect of diffusing the light, the gap
10
also causes the light utilization efficiency to be decreased due to the reflection on the interface with both the elements
3
and
6
.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to provide a light regulation element which is easily manufactured. And, another object of the present invention is to provide a light regulation element which, while regulating the travelling direction of a light emitted from a surface light source device, can convert the light to a diffused light which can satisfy a view angle required for the liquid crystal display. A still another object of the present invention is to provide a light regulation device which can be also applied to a surface light source device for local illumination.
In order to achieve these objects, there is provided a light-penetrable light regulation element having at least one light regulation surface. The shape of the light regulation surface of the light regulation element includes a plurality of concave and convex shape segments (protrusions) for bending the travelling direction of the light penetrating the light regulation element. And, at least either of the light regulation surface or the surface on the side opposite to the light regulation surface is covered with a light diffusion layer, and it is desirable that the turbidity of the layer falls within a range from 1900 cm
−1
to 2400 cm
−1
. The light diffusion layer may include a portion in which the air exists.
Generally, the regulating of the light travelling direction and the allowing of the light to be diffused are opposed to each other. A fact that the light becomes diffused means that the light travelling direction is disturbed, and the regulating of the light travelling direction means the regulating of the light diffusion.
Therefore, it is necessary to set the light diffusion ability of the light diffusion layer provided on the light regulation element so as to obtain a desirable balance with the ability to regulate the light travelling direction.
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Arai Takayuki
Watai Kayoko
Enplas Corporation
Nguyen Thong
Staas & Halsey , LLP
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