Secondary optical design for LED illumination using freeform lens

The purpose of the secondary optical design for light emitting diodes (LED) illumination is to rearrange the direct output of LED and then achieve the desired illumination. Usually a lens is applied to realize this function in an LED illumination system, and a freeform lens can do better than the traditional spherical ones. The method in this paper can be used to design a freeform lens in short time, just less than 10 seconds. And this freeform lens is constructed using the numerical solutions of a set of first-order partial differential equations, which are deduced from the Snell's law according to the conservation of energy. Using an LED as the source while immersing it in the lens, a uniform rectangle can be gotten through single refraction, and with uniformity near to 90%. The rectangular illumination also has a relatively clear cut-off line with little blur at the edge. This method can shorten the designing time and improve the performance of LED illumination system. Furthermore, not only rectangle, but other illumination figures can be achieved by freeform lens designed by this method, which can broaden the scope of freeform lens's usage.