US Patent 7771104 Planar lighting device

The absolute value of the light amount is increased by providing main light sources and auxiliary light sources on four sides of a light guide plate having a flat and rectangular light exit plane whereas the amounts of light emitted by LED chips of the main light sources and the auxiliary light sources are adjusted such that illuminance is highest near the central area of the light guide plate to obtain a high-in-the-middle, bell-curve illuminance distribution for light emitted by the light guide plate. A planar lighting device achieving a reduced thickness and weight and capable of emitting an increased amount of illumination light is provided.