An optimisation of a freeform lens design for LED street lighting

The number of light emitting diodes (LEDs) used in a variety of applications is increasing rapidly. A good example of an application where this is happening is street lighting. The increasing use of LEDs is due to their advantages compared to other sources of illumination. However, LEDs are not without disadvantages. One of their main drawbacks when used for street lighting without an adequate secondary optic is that they tend to produce a circular footprint with high intensity at the centre and low intensity at the edge of the illuminated area, which prevents them from satisfying national and international standards for uniformity of illumination. This paper presents a new energy mapping method to design a freeform lens to generate uniform illumination of over 95% on the target plane. The lenses presented in this paper have been designed with two different entrance apertures: (i) A hemisphere subtracted aperture (ii) a flat entrance aperture.