Application of heterogeneous microlenses for solid state lighting

In this paper, variable separation mapping design method and solving differential equation method were adopted to obtain freeform surface for a square target plane and circular target plane, respectively. Starting from the freeform lens constructed by these methods, we would keep the light field intensity uniform.

We then utilized heterogeneous micro lens array (MLA) to approximate the shape of the freeform lens. We adjusted the curvature radius and size by the simulation results. Through optimization process, we could achieve a uniform light intensity of ight emitting diodes using heterogeneous MLA. The thickness of direct-lit backlight unit is 2 mm thick. This design achieved 96% efficiency and 90% uniformity. It covers an area of 49 square centimeters .