Patent ID: 7719631

Claim:
An optical sheet comprising cylindrical lens elements which have a hyperboloidal face or a paraboloidal face and are provided successively in a row on one of principal faces of said optical sheet, wherein a Z axis is taken in parallel to a normal line direction to said optical sheet and an X axis is taken in a direction of the row of said cylindrical lens elements, and wherein a cross sectional shape of said cylindrical lenses satisfies the following expression: Z=X 2 /( R +√{square root over ( )}( R 2 −(1 +K ) X 2 )) where R is a radius of curvature of a distal end vertex, and K is a conic constant, and wherein the radius R of curvature, the conic constant K and a configuration unit width D satisfy the following numerical ranges: 0<R<D −4 <K≦ 1.