Patent ID: 7316498

Claim:
An optical substrate comprising: at least one prism structure, each of the at least one prism structures having a first surface characterized by a first surface structure function modulated by a second surface structure function, the first surface structure function having characteristics to provide that each of the at least one prism structures has a cross section with at least two curved sides to provide defocusing diffusion to light incident on the substrate, both the first surface structure function and the second surface structure function encompassing the two curved sides, the second surface structure function having characteristics to provide additional diffusion to the light incident on the substrate, wherein each of the at least two curved sides is defined by an equation z = cr 2 1 + 1 - ( 1 + k ) ⁢ c 2 ⁢ r 2 + ∑ i = 1 N ⁢ a i ⁢ r i where a i are coefficients and N is a positive integer greater than 1, z is a perpendicular deviation of a surface of the curved side from a straight line originating at a first reference point and terminating at a second reference point, and where r is the distance along the straight line from the first reference point.