| 摘要 |
PURPOSE:To obtain uniform display free of a difference in brightness by providing a columnar light guide part for guiding irradiation light to a flat diffusion part and a inversely conic reflecting plate for reflecting the irradiation light from the light guide part toward the outer circumference of the diffusion part, and allowing the respective part to meet specific requirements. CONSTITUTION:When the radius of the light guide part 4 is (a) and its height is (d), an inequality tantheta>2na/h h; frequency of reflection within height (h) holds for a critical angle theta. With regard to the reflecting surface 3d for guiding the irradiation light which travels to the surface of the diffusion part 3 at an angle alpha of incidence less than the critical angle to its outer circumference, an inequality b>a(2nt+t+h)/h (t; thickness of diffusion part 3) holds. Thus, the external diameter of the light guide part 4, the height and thickness of the diffusion part 3, the diameter of the reflecting surface 3b formed thereupon, and the critical angle determined by materials are considered when value determined by said two inequalities is selected to obtain the efficient guide. |
