Illumination – Revolving
Reexamination Certificate
2001-12-13
2003-12-30
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S339000, C362S330000, C362S026000
Reexamination Certificate
active
06669350
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a planar light source system using a substantially point-shaped light source such as an LED light source or the like used for a liquid crystal display device or the like, and particularly to a planar light source system which is used for mobile electronic equipment such as a cellular phone, a portable information terminal or personal digital assistant (PDA), an electronic organizer, a game machine, a note type personal computer or the like and is designed to be enhanced in miniaturization and reduced in power consumption, and a light deflecting device used therefor.
DESCRIPTION OF THE RELATED ART
Demands for mobile electronic equipment such as a cellular phone, a portable information terminal or personal digital assistant, an electronic organizer, a game machine, a note type personal computer, etc. has been recently enhanced, and a light source which is reduced in power consumption and designed to have a thin body and also provides high and uniform luminance has been required as a back light source for a liquid crystal display device for such a mobile electronic equipment.
An under-lighting type in which plural linear light sources such as fluorescent lamps or the like are arranged in a housing or an edge-lighting type in which a linear light source is disposed at a side end surface of a planar light guide has been hitherto known as a back light source device used for a liquid crystal display device, a signboard, a traffic direction board or the like. With respect to the under-lighting type back light source, it is difficult to reduce the weight of the light source portion and also reduce the thickness of the light source portion, and also there occurs a see-through phenomenon that fluorescent lamps or the like used as a light source are seen through a display panel.
Therefore, the edge-lighting type has been more frequently used as a light and thin back light source device. Such an edge-lighting type light source device is a planar light source system as described below. That is, according to the planar light source system, a plate-shaped transparent material such as an acrylic resin plate or the like is usually used as a light guide, and a light source is disposed so as to confront the side end surface of the light guide. Light emitted from the light source is introduced into the light guide through the side end surface (light incident face) thereof, and the light thus introduced into the light guide is emitted in a planar shape from a light emission face of the light guide by using a light emission function such as a light diffusing portion formed on a front surface (light emission face) or back surface of the light guide. The light thus emitted by the light emission function is generally emitted in a slant direction to the emission face of the light guide, and thus it is general that an emission direction controller such as a prism sheet or the like is mounted on the light guide to deflect the light in the normal direction of the light emission face of the light guide.
For example, JP(A)-2-84618 or JP(U)-3-69174 has proposed a planar light source system in which a directional light emission structure such as a mat-finished surface or the like is formed on at least one of the light emission face of the light guide and the back surface thereof and a prism sheet having many linear elongated prisms arranged in parallel to each other is mounted on the light emission face. In such a planar light source system, the distribution of the emission light excessively expands, particularly in the vertical and parallel directions (more particularly, in the parallel direction) to the light source, and thus it does not sufficiently satisfy the requirements for low power consumption and high luminance.
Besides, from the viewpoint of reduction in power consumption and miniaturization, an LED light source is being used in a planar light source system for mobile electronic equipment or the like. Such a planar light source system using an LED light source is disclosed in JP(A)-9-81048 or JP(A)-9-152360. According to the disclosure of the former publication, an LED light source is disposed at the side end surface of a light guide, and one of the main surfaces of the light guide is set to a mat-finished surface while linear elongated prisms extending linearly are disposed on the other surface in parallel to the light incident edge. Further, according to the disclosure of the latter publication, an LED light source is disposed at the bottom surface side of a light guide having a prism shape on the back surface thereof, and light incident from the bottom surface is guided with use of a mirror.
According to these planar light source systems described above, light is directed in the normal direction of the emission face of the light guide by the action of the prism shape provided to the light guide. However, since the linear prism extending straightly is formed in parallel to the light incident edge, light emitted from the LED light source in a slant direction cannot be directed in the normal direction of the light emission face of the light guide, so that an area located in the slant direction is dark and thus luminance unevenness occurs.
Furthermore, JP(A)-7-320514 proposes that an LED light source is disposed at the corner portion of a light guide and a diffusing light guide is used, and JP(A)-8-184829 discloses that both the surfaces of a light guide are roughened. However, according to these planar light source systems, light is emitted in a slant direction to the light emission face, and thus the luminance is lowered in the normal direction which is an usual observation direction.
Still furthermore, JP(A)-11-232918 and JP(A)-11-329039 proposes that a diffusion pattern is formed on the back surface of a light guide so that it is disposed discretely and arcuately with respect to a point light source. However, it is impossible for the formation of such a diffusion pattern to efficiently emit light propagating through the light guide in the normal direction of the light emission face of the light guide, so that sufficient luminance cannot be achieved.
Still furthermore, JP(A)-11-167028 or JP(A)-2001-143512 proposes that many elongated prisms or V-shaped grooves are concentrically formed on the front surface or back surface of a light guide with a point light source positioned at the center in a planar light source system using the point light source. By forming such a concentric pattern on the light guide, light can be emitted uniformly over the overall light emission face of the light guide to thereby suppress occurrence of luminance unevenness. However, according to these planar light source system, emission light from the light guide is emitted directly or through a light diffusion film, and the distribution of emission light from the planar light source system has low directionality, so that a planar light source system having high luminance cannot be achieved.
Besides, there is also proposed a planar light source system comprising a light guide having a light diffusion pattern such as a dot pattern or the like printed on a light emission face thereof, a light diffusion film disposed on the light emission face of the light guide, and two prism sheets disposed on the light diffusion film, wherein each of the prism sheets has many linear elongated prisms arranged in parallel to each other, each elongated prism having a right-angled isosceles triangular section, and two prism sheets are arranged so that the elongated prisms thereof are perpendicular to one another. However, according to this planar light source system, it is difficult to efficiently emit directional light emitted from an LED light source in the normal direction, and also the distribution of emission light is excessively expanded, so that the luminance in the normal direction and the light utilization efficiency are lowered.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a planar light source system which is suitably used as a planar ligh
Chiba Issei
Hayashi Yasuko
Yamashita Tomoyoshi
Lee Guiyoung
Mitsubish Rayon Co., Ltd.
Morgan & Lewis & Bockius, LLP
O'Shea Sandra
LandOfFree
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