A novel LED lens for rotationally symmetric uniform illumination

Traditional LED (light emitting diode) packaging always adopts hemisphere lens, and can ensure high light output efficiency, but its radiation pattern yields Lambert distribution and is non-uniformity. To enable LED light sources be applied in uniform illumination system, a method to obtain freeform LED lens based on energy equipartition and tangent iteration is proposed. Firstly, according to the Lambertian distribution of LED light intensity and its rotationally symmetric peculiarity, the LED emission angle is divided into N parts in Two-dimensional coordinate system, and the energy contained in each part is equal; Secondly, the target plane is divided into N equal areas along its radii, and the discrete points are corresponding to the N parts of emission angle. So that if the energy in each divided solid angle is controlled to illuminate the equal divided area, the illumination of each corresponding micro-belt on the target plane will be uniform; Finally, to avoid the total reflection of large emission angle rays, the designed lens will refract the rays with 0~450 emission angle and reflect the rays with 450~900 emission angle. Choosing an initial point on the freeform generatrix, and using Snell equation and tangent iteration method, the coordinates of all points on the freeform generatrix are obtained, which could be rotated into the freeform surface of the lens. The simulation results using the designed LED lens show that for a rotationally symmetric target plane the illumination uniformity is near to 90% and the energy efficiency is higher than 95%.