Light pipe, planar light source unit and reflective liquid-crystal display device

Abstract

A light pipe having a plate-like substance having an upper surface, a lower surface opposite to the upper surface, an incidence side surface, and an end surface opposite to the incidence side surface, the plate-like substance including a light output device formed in the upper surface so that light incident on the incidence side surface is made to exit from the lower surface through the light output device, the light output device being constituted by fine grooves arranged discontinuously so as to face the incidence side surface, each of the fine grooves having a length of not larger than 250 &mgr;m and a depth of not larger than 50 &mgr;m and not larger than ⅕ as large as the length, each of the fine grooves being constituted by a combination of an optical path changing slope inclined to the lower surface at an angle in a range of from 35 to 48 degrees and a steep slope facing the optical path changing slope and inclined to the lower surface at an angle of not lower than 60 degrees. A reflective liquid-crystal display device having a planar light source unit including a light pipe defined above, and a reflective liquid-crystal display panel disposed on the lower surface side of the light pipe.