Freeform surface secondary lens for LED streetlight

Light distribution is a critical issue for using LED streetlight. Roadway illumination requires the LED streetlight to have a rectangular facular with a good uniformity on the roadway and without any light pollution and glare out of the road. The freeform surface equation was deduced according to the Snells law and etendue conservation. Then Pro／Engineer was applied for the freeform surface lens construction. With the Matlab tool, the partial differential equation was solved with the method of finite difference and the data array of the freeform surface was got. Finally, TracePro was applied to simulate this optical system, test and analyze the design result. For this design, the LED streetlight lens has an ellipsoid inner surface and a freeform outer surface. The results show the total uniformity of illumination on the roadway reaches 0.75, while the longitudinal uniformity reaches 0.85.