Patent ID: 7719635

Claim:
An optical sheet composed of transmissive material, comprising: one generally planar surface; and the other surface on which a concavo-convex pattern formed of a convex portion having a triangular top portion and a concave portion of a surface parallel to the one generally planar surface of the optical sheet is formed alternately in a generally parallel array, wherein the triangular top portion is formed in a shape of an isosceles triangle having a base parallel to the one generally planar surface, and the triangular top portion has a basic angle in a range of 40 to 45 degree, wherein the concave portion is formed by filling, with transmissive resin material, a triangular valley bottom portion formed alternately with the triangular top portion in a generally parallel array; wherein the concavo-convex pattern before the filling of the transmissive resin material is a prismatic concavo-convex pattern; and wherein a buried height of the transmissive resin material with which the concave portion in the prismatic concavo-convex pattern is filled, from the valley bottom of the concave portion in the prismatic convaco-convex pattern.