Design of LED refractive optics with predetermined balance of ray deflection angles between inner and outer surfaces

To improve the optical performance of LED-based lighting devices, refractive optical elements are usually used. We propose a novel technique for the computation of free-form optical elements with two refractive surfaces generating the required illuminance or intensity distribution. The proposed approach makes it possible to control the balance of deflection angles between the inner and outer surfaces of the optical element. It has been proved that for the point light source, the maximal efficiency is obtained when each refractive surface performs exactly the half of the required ray deflection. As an example, a set of optical elements producing a uniformly illuminated square region is computed. Simulation of the computed designs with extended sources has shown that the most tolerant solutions to the size of the light source are obtained in the case when the inner surface performs 60-80% of the ray deflection, and the outer surface performs the remaining 20-40%. The influence of deflection balance on the size of the optical element is discussed.