Modeling and optimization of freeform lenses for LED street lighting

Freeform surfaces are widely used in optical design for LED street lighting. A proper non-symmetrical light distribution on the road can be obtained with LEDs and freeform lenses. There are some mathematical methods to model freeform surfaces: e.g. Bezier-splines, B-splines or NURBS. In this case, freeform surface will be determined by a limited number of control points. Several dozens of control points can be required for each surface. This means a large parameter space for optimization. In order to perform lens optimization efficiently, a good start system has to be defined. It can be done by using some analytical methods, which based on calculated solutions under simplified conditions (e.g. point source, lambert light distribution). Once the start system is determined, lens optimization for non-ideal optical system (measured LED ray-dataset, additional glass cover and so on) can be started. In this work, some practical examples for modeling and optimization of freeform lenses for street lighting will be demonstrated and discussed. Simulated results will be compared with measured data.