Patent ID: 6966673

Claim:
A light distribution control device comprising a substantially plate-like or film-like light diffusion structure which transmits or reflects light and at least one surface of which has a number of ridges arranged parallel to each other, the section of each ridge taken in a direction perpendicular to the longitudinal direction substantially constituting a part of a circle, the surface of each ridge being smooth enough not to cause significant irregular diffusion of light, in a diffraction grating effect attributable to the parallel arrangement of a number of ridges, the ratio of diffraction light quantity to incidence light quantity being adjusted through selection of the angle of circumference and maximum diameter of the section of each ridge, when light is caused to enter a surface of the light diffusion structure, the projection of diffusion distribution onto a plane perpendicular to both the longitudinal direction of the ridges and the surface of the structure being substantially symmetrical with respect to the normal at the point of incidence independently of the angle of incidence of the light.