Patent ID: 7857475

Claim:
A direct-type backlight device comprising: a plurality of linear light sources disposed in approximately parallel, a reflecting plate having a flat plane surface which reflects light from the linear light sources and a platy light diffusing member receiving, diffusing and emitting direct light from said linear light sources and reflected light from said reflecting plate, wherein a distance (a) between centers of the adjacent linear light sources of said plurality of linear light sources is 30 to 65 mm, wherein said light diffusing member comprises an approximately flat light incident plane on a surface facing said linear light sources and a light outgoing plane having a prism row of a plurality of aligned linear prisms extending in approximately parallel to a longitudinal direction of said linear light sources, wherein said linear prism has two inclined surfaces having an approximately equal tilt angle against a plane which is perpendicular to a thickness direction of the light diffusing member, and a cross sectional shape of the linear prism in a crosswise direction is a triangle, and wherein a relationship of (a)/7<L<(a)/4 is satisfied wherein L is a distance (mm) between a central position of one image of two images on said light outgoing plane both corresponding to one linear light source among said plurality of linear light sources, and a position at which a center of said one linear light source is projected on said light outgoing plane.