Prism array used in the surface light source device and image display apparatus using the surface light source device, the surface light source device

摘要

PROBLEM TO BE SOLVED: To provide a surface light source device having high directivity by forming a surface light source device of a back light type in such a manner that the directions of the light emitted from a light transmission plate are aligned to one direction. SOLUTION: Light condensing patterns 58 of a relatively large average angle of inclination are formed on one surface, for example, exit surface 56, of the light transmission plate 52 arranged with a wire-shaped light source 54 on an incident side face 53. The other surface is provided with deflection patterns 57 of the relatively small average angle of inclination. The reflected light is deflected to the angle decreasing little by little in the direction perpendicular to the exit surface 56 when the rays in the light transmission plate 52 are reflected by these deflection patterns 57. The rays are emitted in a direction nearly parallel with the exit surface at a small elevation angle with the exit surface 56 and further the rays spreading laterally are condensed to one direction by the light condensing patterns 58 when the reflection is repeated and the angle of the rays exceed the critical angle of total reflection.