配光是LED路灯应用的主要技术问题之一。道路照明要求LED路灯在路面为均匀性良好的矩形光斑，在道路外无污染，无眩光。采用Snell定律和光源扩展度守恒原理确定自由曲面的解析方程，借助Matlab工具，采用差分法求解建立的偏微分方程，得到自由曲面的数据组，用作图软件Pro/Engineer为自由曲面透镜建模，通过计算机仿真软件TracePro进行光路仿真检验设计结果，并对所得结果进行分析。设计一款内表面为椭球面，外表面为自由曲面的LED路灯透镜，实现了路面光照总均匀度0.75，纵向均匀度0.85的效果。

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.