Donohue, R. and Joseph, B., "Faceted Reflector Fog Lamp Eliminates Lens Fluting," SAE Technical Paper 730279, 1973, doi:10.4271/730279.
In the faceted reflector design for automotive lamps, the reflector is divided into easy-to-fabricate, circular cylindrical segments (facets) in a manner such that the reflector alone produces the beam pattern. The prescription for the facets is developed with the aid of computer programs which simulate the images from each facet and “build up” the desired light pattern mathematically, thus eliminating the normal “cut-and-try” experimental buildup.The design procedure was applied to a fog lamp with a 55 W quartz-halogen bulb and several prototypes have been constructed. The broad beam pattern from these lamps is most suitable for driving in a fog and the lamp with a clear lens offers styling flexibility. The faceted reflector concept can also be applied to headlamps, driving lamps, and signal lamps.