LED Headlight Architecture that creates a High Quality Beam Pattern independent of LED Shortcomings Oliver Dross 1a , Aleksandra Cvetkovic c , Julio Chaves b , Pablo Benítez c , Juan C. Miñano c a LPI Europe, Marques de Urquijo 14, 5D, 28008 Madrid, Spain b Light Prescriptions Innovators LLC, 16662 Hale Ave., Irvine, CA 92606, US c CEDINT Technical University of Madrid (UPM), ETSI Telecomunicación, C. Universitaria, 28040 Madrid, Spain ABSTRACT One of the most challenging applications for high brightness LEDs is in automotive headlights. Optical designs for a low or high beam headlights are plagued by the low flux and luminance of LEDs compared to HID or incandescent sources, by mechanical chip placement tolerances and by color and flux variations between different LEDs. Furthermore the creation of a sharp cutoff is very difficult without baffles or other lossy devices. We present a novel LED headlight design that addresses all of the above problems by mixing the light of several LEDs first in a tailored light guide called LED combiner, thereby reducing color and flux variations between different LEDs and illuminance and color variations across the LED surfaces. The LED combiner forms a virtual source tailored to the application. The illuminance distribution of this virtual source facilitates the generation of the desired intensity pattern by projecting it into the far field. The projection is accomplished by one refractive and one reflective freeform surface calculated by the 3D SMS method. A high quality intensity pattern shape and a very sharp cutoff are created tolerant to LED to optics misalignment and illuminance variations across the LED surface. A low and high beam design with more than 75% total optical efficiency (without cover lens) and performance as latest HID headlights have been achieved. Furthermore it is shown that the architecture has similar tolerance requirements as conventional mass produced headlights. Keywords: SMS Design, Non imaging optics, LED headlight, LED combiner 1. INTRODUCTION LEDs have been applied successfully in all exterior automotive lighting devices but full headlights. Long life time of LEDs (much longer than the car use time if thermal stress is avoided), compactness, instant switch on, lower power consumption, high color temperature, and, maybe even more important, unique styling possibilities to give cars a high tech look and to distinguish them from competitors, are major drivers for the development of LED front lighting. However, the price of an LED headlight will be much higher than incandescent or even HID solutions and optical, mechanical and thermal hurdles have to be overcome before LEDs will be seen on production car front lights. The cooling of the LED has to be completely conductive as LEDs do not emit energy that is not converted into light as infrared radiation. To solve this problem, new ultra low thermal resistance LED packages on metal core PCB in contact to the lamp housing are utilized. The mechanical design, as will be shown later, is closely connected to the optical performance of an LED headlight as the light of many LEDs has to be bundled with high precision to meet legal specifications and driver comfort. The optical design that will collect the LEDs light and form a legal beam pattern must take mechanical issues as placing tolerances of LEDs into account and it must be efficient to maximize the use of the expensive and still sparse LED flux. Design approaches, developed over many decades for incandescent lighting, fail for LEDs due to their completely different optical behavior. 1 *Odross@LPI-Europe.com ; phone +34 915 401 044; fax +34 915 596 082; www.lpi-llc.com