A surface light source device used in an LCD includes a panel-shaped light guide plate, a pair of light sources for emitting light, and two pairs of light source holders. The original plate includes a substrate and N patterns differing from one another in shape. The supports may be used on a flat surface such as a floor or may be mounted on an independently positioned pair of rails for mounting between a mattress and a box spring by means of posts which are removably received in an opening in the crescent shaped supports and adjustably locked in an opening in each rail.