Patent ID: 7033736

Claim:
A method for making a structured screen that provides a desired spread of incident light, said structured screen comprising a substrate and a plurality of microstructures distributed over at least one surface of said substrate, said method comprising: (a) selecting a location on said at least one surface of the substrate for each of said plurality of microstructures; (b) selecting a configuration for each of said plurality of microstructures; (c) calculating the spread of the incident light for the selected locations and the selected configurations of steps (a) and (b); (d) comparing the calculated spread of step (c) with the desired spread and, if necessary, repeating at least one of steps (a) and (b), and step (c) until the comparison between the calculated spread and desired spread satisfies a specified criterion; and (e) producing a plurality of microstructures having, to an accuracy of better than 10·λ n , the locations and the configurations which, in step (d), resulted in the satisfaction of the specified criterion, where λn is the nominal operating wavelength for the screens, wherein at least some of the microstructures comprise a curved microlens portion or a triangular portion or a pyramidal portion.