Freeform reflector design for LED street lighting

Faceted freeform reflectors were designed for intelligent street lighting with LED cluster arrays for main traffic roads. Special attention was paid to achieve highly efficient illumination on both wet and dry road surfaces. CIE reflection tables W4 and C2 were applied in the simulation for these two conditions, respectively. The reflector design started with plane facets, then - to avoid artifacts from the images of the individual LEDs - plane facets were replaced with cylindrical facets. To get even more flexibility for the design and optimization, freeform facets were employed, modeled by extruding two different conic curves together. Besides of achieving well-proportioned road luminance distribution, the basic shapes of the reflectors were formed to control stray light caused by multiple reflections within the reflector and by reflection of light from neighbor clusters within the cluster array. The merit functions include useful transmission of light to the road as well as overall and lengthwise uniformity according to road illumination standards. Due to the large amount of variables, the optimization was carried out sequentially facet by facet. The design loops included compromising with manufacturing limitations for plastics molding and thorough analysis of conformity with DIN EN 13201 standards for ME road lighting classes. The calculated reflector profiles are realized by plastic injection molding.