Patent ID: 7510308

Claim:
A diffusing sheet that is used in a surface light source device of direct type including a light source unit having a plurality of light sources arranged in parallel, and that diffuses light from the light sources in the light source unit to make the light uniform, the diffusing sheet comprising: at least on its light-emerging side surface, a diffusion lens array having a plurality of unit lenses that allow light from the light sources in the light source unit to be diffused and to emerge from the unit lenses, wherein the diffusion lens array includes at least two different types of a unit lens that are regularly arranged on a sheet face, each of the two types of a unit lens at least is in one shape selected from a shape equivalent to a part of an elliptic cylinder having an elliptical section and a shape equivalent to a part of a spheroid having an elliptical section, and a major axis of the elliptical section of each of the unit lenses is perpendicular to the sheet face.