Design of LED Collimating lens for uniform illumination with freeform surface

The collimating lens used for uniform illumination has been widely used in lighting engineering as the LED secondary optics. A novel lens structure including four freeform surfaces is designed in this paper, the freeform surfaces can be constructed by an iterative process, which is based on nonimaging optics and geometrical optics. This method can be used not only for Lambertian-type LED source, but also for near-Lambertian-type LED source. Since the LED source is regarded as a point source during the design process, in order to verify the feasibility of the design method, an LED chip whose size is 1 mm *1 mm is used in the simulation. Three lens models with different initial parameters are established for optical simulation. The simulation results show that the total optical efficiency is greater than 87%, the uniformity is greater than 0.93, and the full width at half maxima (FWHM) is approximately 2 * 2 degrees. The performance difference of the three models is small, which indicates that the initial parameters have little effect on the lens performance under certain conditions.