Efficient freeform optics for street lighting applications

The recent developments in LED technology have created an attractive light source for new efficient illumination systems. However, their high luminous efficacy can only be fully exploited in combination with highly efficient optics, allowing to tailor the light into a given target irradiance. The design of freeform optics is now the privileged route to tackle this challenge: using relatively few optical components, a complex non-radially symmetric irradiance pattern can be achieved. Combining these capabilities with a high optical efficiency brings up new problems and leads to sensitive numerical schemes. We report in this paper on the recent developments of our method to design two freeform optical surfaces (either refractive or reflective) using an optimized ray mapping computation. The procedure relies on the Monge-Kantorovich theory of optimal mass transport, and the related conditions for an optimal mapping. We illustrate our procedure with the design of an efficient street lighting lens, achieving an optical efficiency over 85% while at the same time producing a homogeneous luminance pattern on the road.