Direct-type backlight device

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.