Patent ID: 8118469

Claim:
A surface illuminating device comprising: a plurality of linear light sources arranged in parallel to each other in a plane; a light-transmissive optical sheet including a luminance-distribution control layer formed on a light exit surface of the optical sheet, the luminance-distribution control layer decreasing unevenness in luminance of light emitted from the linear light sources; and a reflection surface positioned opposite to the optical sheet with the linear light sources interposed therebetween, the reflection surface reflecting the light emitted from the linear light sources, wherein the luminance-distribution control layer of the optical sheet includes a plurality of protrusions, the protrusions having ridgelines extending substantially in parallel to an extending direction of the linear light sources and being arranged continuously in an arrangement direction of the linear light sources, and wherein, in a range of 0≦x≦L/2, inclination angles of some or all the protrusions increase relative to a Z direction as the protrusions are located farther from the position of x=0 in the X direction, where an X direction represents the arrangement direction of the linear light sources, a Y direction represents the extending direction of the linear light sources, the Z direction represents a direction orthogonal to the X and Y directions, an inter-light-source distance L represents a distance between the centers of adjacent linear light sources from among the linear light sources, and x=0 at the centers of the linear light sources and increases to L/2 at the center positions between adjacent linear light sources.