Planar lighting device

A planar lighting device comprising:

• linear light sources arranged in parallel to each other;
• a light guide plate comprising a flat light exit surface, a rear surface opposite to said light exit surface and parallel grooves formed in said rear surface, for accommodating said linear light sources, respectively, wherein a cross-section of said light guide plate perpendicular to said parallel grooves has a rear surface profile of said rear surface such that convex portions are formed at respective portions where said parallel grooves are formed, while concave portions are formed between adjacent parallel grooves, and a thickness of said light guide plate in each concave portion decreases from each parallel groove toward either midpoint between adjacent parallel grooves and is thinnest at said midpoint;
• and
• a support member arranged in a side of said rear surface of said light guide plate, for supporting said light guide plate,
• wherein said support member has a first surface facing said rear surface of said light guide plate and a second surface opposite to said first surface, and
• wherein a cross-section of said support member perpendicular to said parallel grooves of said light guide plate has a first surface profile on a side of said support member facing said light guide plate such that a profile of a portion facing each convex portion of said rear surface profile of said light guide plate is identical to a profile of each concave portion of said rear surface profile of said light guide plate, while said second surface of said support member is a flat surface.