Patent ID: 7125131

Claim:
An optical substrate comprising: a surface comprising a prism structure characterized by a cross section having a curved facet described by the equation z = cr 2 1 + 1 - ( 1 + k ) ⁢ c 2 ⁢ r 2 + dr 2 + er 4 + fr 6 , wherein z is the perpendicular deviation of the surface of the facet of the prism from a straight line originating at a first reference point and terminating at a second reference point and the coefficients of the polynomial lie within the following approximate ranges: −20 <c <20; −10 <d <10; −10 <e <10; −10 <f <10 and −1 <k is less than or equal to zero and where r the distance along the straight line from the first reference point, wherein the prism structure comprises a plurality of prisms having a prescribed peak angle, α, a height, h, a length, l , and a pitch, p, and the plurality of prisms include at least a pseudorandom peak angle, α, height, h, length, l , or pitch, p.