Patent ID: 7688507

Claim:
A diffusion sheet that diffuses light incident thereon from a light incident side and causes the light to outgo from a light outgoing side, characterized by comprising: a plurality of approximately trapezoidal columnar unit lens portions disposed such that long-axis directions thereof are in parallel with each other, wherein all surfaces of the unit lens portions, which correspond to long bottom segments of approximately trapezoidal sections of the unit lens portions vertical to the long-axis directions thereof, are disposed on a light-incident-side flat surface; and a plurality of light absorbing portions interposed between adjacent unit lens portions of the plurality of unit lens portions to absorb external light incident from the light outgoing side, wherein the plurality of unit lens portions are arranged such that a part of the light incident on the unit lens portions from the light incident side is totally reflected on surfaces of the unit lens portions corresponding to side segments of the approximately trapezoidal sections vertical to the long-axis directions of the unit lens portions, and a section of each of the light absorbing portions vertical to a long-axis direction thereof interposed between adjacent unit lens portions of the plurality of unit lens portions is formed in an approximately triangular shape, and a vertex of the section on the light incident side thereof is composed of a curved line segment having a radius of curvature of at least 1 μm.