Patent ID: 7802895

Claim:
A direct-type backlight device comprising: a reflecting plate; a plurality of point light sources; and a light diffusing plate which receives direct light from said point light sources and reflected light from said reflecting plate on a light receiving surface thereof, and then diffuses and emits the light from a light emitting surface thereof, said reflecting plate, said point light sources and said light diffusing plate being placed in this order, wherein: at least either one of said reflecting plate and said light diffusing plate is provided with an image forming position adjusting member which produces images A 1 , B 1 , C 1 and D 1 of the point light sources A, B, C and D, respectively, on said light emitting surface, said four point light sources A, B, C and D being selected among said plurality of point light sources such that said four point light sources constitute a convex quadrilateral which has the smallest area and the shortest circumference length, and said images A 1 , B 1 , C 1 and D 1 being observed within a specific region which satisfies the following relationships (1) to (4) in a region surrounded by positions A 0 , B 0 , C 0 and D 0 which are positions of the projected image of the point light sources A, B, C and D on said light diffusing plate: 0.8× L ( A 0 C 0 )> L ( A 0 A 1 )>0.2× L ( A 0 C 0 ) (1) 0.8× L ( A 0 C 0 )> L ( C 0 C 1 )>0.2× L ( A 0 C 0 ) (2) 0.8× L ( B 0 D 0 )> L ( B 0 B 1 )>0.2× L ( B 0 D 0 ) (3) 0.8× L ( B 0 D 0 )> L ( D 0 D 1 )>0.2× L ( B 0 D 0 ) (4); wherein L(XY) indicates a length of a line segment XY.