Uniform Illumination for Nonplanar Surface Based on Freeform Surfaces

The shapes of target surfaces are nonplanar on many occasions such as undulating road and roof of the tunnel, while the lighting quality generated by traditional nonimaging optical lenses still needs to be further improved. As a result, a novel method is proposed for the design of optical elements generating uniform irradiance distribution on nonplanar target surfaces. A matrix is introduced instead of a single height parameter for improving the mathematical model of asymmetrical lenses, hence a modified mathematical model based on single LED chip and desired irradiance distribution of the nonplanar target surface is established. By solving the equations with the iterative method, the asymmetrical lenses can be obtained through commercial CAD tools. Three different nonplanar surfaces are used to verify the validity of the proposed method, including an inner-spherical surface, undulating surface and arched surface. The results show that the illumination uniformity of the target surface can reach over 70%, and the light efficiency is more than 83%, which are much better than that generated by traditional methods.