Plane light source unit and light guide used therein

摘要

A plane light source unit includes a tubular light source, and a light guide. The light guide has a light emitting surface and a reflecting surface in addition to a light incident face placed near the tubular light source to receive light emitted from the tubular light source. The light guide has a plurality of projections or grooves arrayed on the light emitting surface to extend parallel to each other along a longitudinal direction of the tubular light source so as to cause the light incident from the light incident face to emerge from the light emitting surface. The height or depth of each of the projections or grooves increases from the central portion to the two end portions in the longitudinal direction of the tubular light source.