Florian Fournier, William Cassarly and Jannick P. Rolland published a paper, ‘Fast freeform reflector generation using source-target maps,’ in Optics Express 18(5), 5295-5304 (2010)
Abstract: We propose a freeform reflector design method based on the mapping of equi-flux grids between a point source and a target. This method imposes no restriction on the target distribution, the reflector collection angle or the source intensity pattern. Source-target maps are generated from a small number of target points using the Oliker algorithm. Such maps satisfy the surface integrability condition and can thus be used to quickly generate reflectors that produce continuous illuminance distributions.