Double freeform surfaces lens design for LED uniform illumination with high distance–height ratio

• A novel method for the design of an LED DFS lens is proposed.
• An effective feedback method is introduced to optimize the DFS lens.
• The DFS lens can be used in high DHR lighting systems.
• A high illuminance uniformity and system efficiency is achieved.
• The DFS lens has a compact size and is eligible for production.

A practical method is proposed to design a double freeform surfaces (DFS) lens for LED sources, in order to form uniform illumination in the high distance–height ratio (DHR) lighting system. The ray mapping relationship is first established between the solid angle of the source and the target plane according to the energy conservation law and the variable separation method. A DFS lens is then constructed simultaneously and point by point to the ray mapping based on the Snell's law. Optical performance of the lens is investigated by the Monte Carlo method. A simple and effective method is utilized to optimize the lens design in accordance with the simulation results. As an example, a DFS lens with DHR of 2.5 (distance 30 mm, height 12 mm) is designed by the proposed method. Compared with the traditional methods, the illuminance uniformity is significantly improved from 67.20% to 86.43% and the size of the lens is dramatically reduced.