Patent ID: 7528901

Claim:
A backlight device comprising: a light guiding plate disposed on a drive substrate directly attached with a light source arranged such that light from the light source is emitted into the light guiding plate; and a diffusion sheet and a prism sheet superimposed on the light guiding plate, and arranged to refract the light emitted into the light guiding plate, and to emit the light from a front surface of the prism sheet, the prism sheet extending toward the light source, and covering above a gap between the light source and the light guiding plate, wherein the prism sheet includes a plurality of substantially triangular protrusions disposed on a surface of the prism sheet to extend parallel to each other, and each having a saw-toothed section; the prism sheet includes a first prism sheet disposed so that ridgelines of the protrusions having the substantially triangular section extend substantially perpendicular to the light emitting surface of the light source, and a second prism sheet disposed so that ridgelines of the protrusions having the substantially triangular section extend substantially parallel to the light emitting surface of the light source; and the first prism sheet covers above the gap between the light source and the light guiding plate, wherein the first prism sheet is provided with a slit located at a position on a center side of a position just above the gap between the light source and the light guiding plate, and the slit of the first prism sheet extends across the plurality of the protrusions having the substantially triangular section.