Illumination – Revolving
Reexamination Certificate
1998-08-10
2001-09-18
Sember, Thomas M. (Department: 2875)
Illumination
Revolving
C362S330000, C362S331000, C362S339000
Reexamination Certificate
active
06290364
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
This invention relates to a surface light source device. In more detail, the invention relates to a surface light source device using an optical element (hereinafter referred to as “a scattering light conducting element”) having a function to conduct an incident light while scattering in a volume region. The invention can be adapted to an optional application requiring a high uniform emitting light flux, and in particular, effectively utilized as a display backlight source means of a liquid crystal display device, etc.
II. Description of the Prior Art
Conventionally, heretofore known are various kinds of surface light source devices of the type capable of emitting the light in a desired direction using the scattering phenomenon, those of which are used for a backlight source of the liquid crystal display devices or the like.
One similar type of such known surface light source devices, includes a light emitting panel in which a light incident means is provided on a lateral side of a light conducting element made of a plate shaped transparent material, a reflection element is provided on a back surface-side, and a light scattering property is given adjacent a front surface-side surface to produce a light emitting surface, and which is used as a backlight of the liquid crystal display device and the like.
Such devices are disclosed in Japanese Patent Laid Opens Sho-62-235905 in 1987, Sho-63-63083 in 1988, Hei-2-13925 in 1990, and Hei-2-245787 in 1990.
Those surface light source devices, spreading in the light emitting direction are produced by irregular reflection or mirror reflection adjacent to the light conducting element or on reflection elements, and the light scattering is not generated in a volume shape from inside of the light conducting means, Therefore, it is theoretically difficult to sufficiently raise a rate of scattering light outputted from the scattering light conducting device.
In the surface light source device, to obtain a uniform irradiation degree, a tilt depending on distance from the light incident means must be given to reflectivity of the reflection element as shown in the known disclosures above. This introduces a complicated larger type structure together with a higher manufacturing cost.
When the surface light source device is used for the backlight of the liquid crystal display devices and the like, there must be sacrificed some of requirements such as brightness, uniformity of irradiation degree, a thinner construction, and economy and the like.
As a second similar type of the known surface light source devices there is used a light diffusing plate in which particle substances having a different refractive index from an extended plate shaped transparent material are diffused into the inside of the transparent material.
The similar types of those are disclosed in Japanese Utility Model Registration Patent Application Laid Open Sho-51-89888 in 1976, Japanese Patent Application Laid Opens Hei-1-172801 in 1989, Hei-1236257 in 1989, Hei-1-269901 in 1989, Hei-2-221925 in 1990, and Hei-4-145485 in 1992.
Japanese Patent Application Laid Opens Hei-2221925 in 1990 and Hei-4-145485 disclose that a light is incident from lateral side of the plate shaped light scattering conducting element, where a reflection element is arranged on surface side of one-side, the other side surface is made a light emitting surface, and this forms a backlight source of the liquid crystal display device and the like.
In these arrangements, a light scattering arises in a volume shaped manner due to irregularity of the refractive index produced by the particle substances scattered and mixed into the inside of the transparent element.
However, various counter measures to uniform illuminance as a surface light source in those surface light source device are employed; namely, to give a gradient to a diffusing concentration of the particle substance which is diffused into the scattering light conducting element; to provide a scattering enforcement means such as mesh shape or dot shape by using light dispersing ink and the like on the back-side of the light scattering conducting element; or in some cases to give a gradient on a density of the mesh shape or the dot shape.
Conventionally, there has been employed a method comprising the step of, raising at most the light scattering power where a scattering power is lowered at a part adjacent to a light source together with the decrease of the scattering power at a portion adjacent to the light source, or raising the light scattering power at most including an enforcement layer of a mesh shape or a dot shape on the backside at a position apart from the light source.
In the background where conventionally the method as described above has been employed, in fact it is an advantage that, to avoid deterioration of illuminance apart from the light source, there must be provided a gradient of the light scattering power in any form depending on a distance from the light source in the case where the light scattering conducting light element is formed by dispersing particles having a different refractive index into the matrix, in addition to a history where it has been considered that generally a scattering enforcement means of a back surface region of the scattering light conducting element is indispensable for maintaining the required amount of scattering light, in the ordinary sized scattering light conducting element.
For another form of technique of the second similar type, it is proposed that a shape of the light scattering conducting element is made a wedge shape or a triangle roof shape, and without providing gradient to a different refractive index substance diffusion density itself within one light scattering conducting element.
For example, Japanese patent Laid Open Hei-4-140783 in 1992 disclosed the surface light source device using a plate shaped member combined by a relationship in that a light scattering conducting element (an opalescent substrate) having a mountain (L character) shaped sectional view is arranged apart from an object to be illuminated, and a transparent substrate having a complementary shape thereto is arranged in the vicinity of a side of the object to be illuminated. A light source is disposed on a lateral side of the plate shaped member. In the surface light source device, a light emitted from the light source travels mainly through the transparent substrate to be incident on the opalescent substrate, where the scattered light travels again through the transparent substrate to be emitted from a surface adjacent a side of the object to be illuminated. As a result, passing two times through a boundary surface between the opalescent substrate and the transparent substrate, this then produces a larger light loss disadvantageously.
A surface light source device has been proposed in which, using the so called injection type polymerization, the light scattering conducting element is formed into one sheet of plate shape by combining two wedge type light scattering conducting elements having different scattering powers which have allowed different refractive index substances to uniformly disperse into each polymer matrix, and thus, a light is incident from the lateral direction (see “PCT/JP92/01230”, “Polymer Reprints, Japan Vol. 41, No. 3; 1992”, p802, and “Polymer Reprints, Japan Vol. 41, No. 7; 1992”, p2945 to 2947).
In the prior art, it is difficult to raise an efficiency for light utilization of the surface light source device in that the light is incident from a lateral direction of a transparent materiel of an extending plate shape and a reflecting element is arranged on one-side surface and a light diffusion property is given adjacent to the other-side front surface. If a rise of illuminance of the light emitting surface is intended, the various enforcement means are more required with the increase of a thickness of the device, producing a disadvantage economically.
In the type using such transparent plate, in the case where a mesh or dot shaped enforcement layer is
Arai Takayuki
Koike Yasuhiro
Enplas Corporation
Sember Thomas M.
Staas & Halsey , LLP
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