Patent ID: 6819372
Filing Date: 2004-11-16
Classification: G02B

Abstract:
A back light device comprising:a light source; a lightconductor in a substantial plate form comprising a front face, a back face and side end faces, light radiated from the light source and made incident on the one of the side end faces being output as a first diffused light having a peak oblique lo the normal standing on a light outputting surface therefrom which is the front face; at least one light diffusing sheet for receiving, on its face, the first diffused light output from the light outputting surface of the lightconductor, and outputting a second diffused light having a directivity from a light outputting surface of the diffusing sheet opposite to the face of the diffusing sheet, the light outputting surface of the light diffusing sheet being rougher than the face of the at least one light diffusing sheet, the tight diffusing sheet has a haze value of 30% or more and shifts the direction of the maximum intensity of the second diffused light toward the direction of the normal standing on the light outputting surface of the diffusing sheet by virtue of the rougher light outputting surface; a polarized beam splitting sheet which receives the second diffused light from the light outputting surface of the light diffusing sheet, through which one polarized light component of the second diffused light is transmitted, and on which the other polarized light component is reflected; and a light reflecting sheet which is arranged on the back face of the lightconductor and is for reflecting a light into the lightconductor, the light diffusing reflectivity of the light reflecting sheet being 70 or more.