PLANAR LIGHT SOURCE

摘要

PROBLEM TO BE SOLVED: To embody a plane light source having a high contrast and high directivity capable of embodying such an extremely narrow visual field angle as the light source is hardly visible from others. SOLUTION: This plane light source includes a light transmission plate 9 which has one surface part facing a display side and other surface particularly on an opposite side and is capable of guiding the light from a light source part 3 arranged at least one flank side to the display side described above. The one surface part of the light transmission plate is at least approximately flat and such a prism array 11p in which prisms are lined up to a saw tooth form is formed in the other surface part of the light transmission plate. The ridge lines of the prism array 11p are approximately parallel with the longitudinal direction of the light source part. Such sloped parts 9c of the respective prisms which are nearer to the one surface part of the light transmission plate the furtherer from the light source part 3 exhibit the angle of inclination of the angle sharp to the one surface part of the light transmission plate. This angle of inclination is about 44 deg..