The design and usage of freeform optical elements for illumination application have seen a lot of activity recently. The mathematical methods characterizing optical freeform surfaces are known and have been implemented into commercial illumination design software tools. Users of such software tools are now able to design freeform elements creating arbitrary light distributions. Freeform illumination optics couple light from a source to a target using freeform surfaces. The designer has to balance performance criteria like collection efficiency and achieving an ideal target distribution with the way that the freeform surface(s) must change. Although the increasing power of freeform illumination design tools allows freeform surface to be computed automatically, the designer must still contend with how freeform surfaces change to achieve the desired performance. This paper examines some of the common tradeoffs with special emphasis on how the shape of the freeform surfaces changes. Offsets due to Fresnel losses and limitations to the target illumination distribution generated by extended light sources are covered as well. We also give an overview about common freeform optics application in the industry.
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