Modeling and design of diffuse transmissive free-form surface based on LED collimation effect

Abstract

An indirect illumination pattern with light-emitting diodes (LED) and diffuse transmissive free-form surface was proposed, and in this paper, we designed an ultra-compact rotational symmetric lens with double free-form surfaces based on the edge-ray principle. Based on the Lambertian characteristic of LEDs and ideal diffuse transmissive surface (e.g. frosted glass), a mathematical model was constructed. The coordinates of profile curve of the transmitting part are calculated by Matlab according to the Snell’s law and iterative method at first. Then the TIR lens model is established with Solidworks. The diffuse transmissive free-form surface is constructed by solving a series of equations numerically. The inner surface was elliptic and the outer surface was diffuse transmissive free-form. Furthermore, to keep the optical system compact and provide enough space for the LED, the size of the designed lens model was also greatly reduced. Finally, the results show better uniformity and higher efficiency comparing with the single diffuse transmissive free-form surfaces and flats, and the size of the lens was dramatically reduced. The Monte-Carlo ray-tracing result shows an illumination circular area with a clear cut-off at R = 150 mm at the target plane in a distance H = 600 mm for the near-field illumination. The uniformity within the target illumination area is greater than 86%.