Designing optical free-form surfaces for extended sources

Abstract

LED lighting has been a strongly growing field for the last decade. The outstanding features of LED, like compactness and low operating temperature take the control of light distributions to a new level. Key for this is the development of sophisticated optical elements that distribute the light as intended. The optics design method known as tailoring relies on the point source assumption. This assumption holds as long as the optical element is large compared to the LED chip. With chip sizes of 1 mm² this is of no concern if each chip is endowed with its own optic. To increase the power of a luminaire, LED chips are arranged to form light engines that reach several cm in diameter. In order to save costs and space it is often desirable to use a single optical element for the light engine. At the same time the scale of the optics must not be increased in order to trivially keep the point source assumption valid. For such design tasks point source algorithms are of limited usefulness. New methods that take into account the extent of the light source have to be developed. We present two such extended source methods. The first method iteratively adapts the target light distribution that is fed into a points source method while the second method employs a full phase space description of the optical system.

Irradiance tailoring for extended sources in 3D by implicit integral equation solution

“…The difficulty, as identified by Wester et al [15], is in efficiently evaluating the integral in Eq. 1.…”

Illumination design for extended sources based on phase space mapping

“…Lightemitting diodes in particular exhibit a large etendue due to their extended emission area and Lambertian intensity pattern, which needs to be considered during illumination design. 8,9 Solar applications, especially concentrators, are limited by the size of the sun. Lasers, especially poor quality lasers or lasers with pointing tolerances, have nonvanishing etendue, which needs to be considered.…”

Direct design of aspherical lenses for extended non-Lambertian sources in three-dimensional rotational geometry

“…However, there is still no effective direct method that can be applied to the rotational cases or the freeform cases for extended non-Lambertian sources. Some illuminance compensation approaches [16][17][18][19] can be applied to rotational cases or freeform cases for extended non-Lambertian sources under certain conditions. The key to these compensation methods is iteratively using illuminance compensation to improve the performance of a design created by a zero-étendue method during each iteration.…”