LED light sources are finding ever increasing application in illumination. LEDs have many advantages, such as high efficiency, long life, compactness, directional light emission, mechanical resistance, low-temperature operation, light color control and low UV or IR emissions. These and other advantages make them very well suited for general illumination applications as well as flashlights, car headlights, backlights, or frontlights. In most applications, LEDs are combined with optics to direct their light output. Brighter LEDs have a smaller emission area and, therefore, may be coupled to smaller optics. This is very important in many applications where compactness is crucial, particularly automotive headlamps. When LED brightness is insufficient, it can be augmented by recirculating part of the emitted light back to the LED's emitting surface. This increase in brightness comes at the expense of a reduced flux-emission. As an example, the brightness of an LED with a diffuse reflectivity of 70% may be increased by nearly that much if it is coupled to a high-efficiency recirculating optic. Such augmentation, however, comes at the expense of a flux reduction, as much as 50%. Several optical geometries are explored in this paper to achieve that recirculation together with raytracing results using on a simple model of an LED. Also a number of optical architectures will be shown that escape the classical nonimaging etendue limit associated with traditional optics.

Date Published: 2 September 2008
PDF: 12 pages
Proc. SPIE 7059, Nonimaging Optics and Efficient Illumination Systems V, 705902 (2 September 2008); doi: 10.1117/12.794626

Published in SPIE Proceedings Vol. 7059:
Nonimaging Optics and Efficient Illumination Systems V
Roland Winston; R. John Koshel, Editor(s)