Multi Chip on Board LEDs versus Assembly of Chip Size LEDs: Impact on Optics Design for Headlamps

Dr.Alexander Guenther

LEDApplications Engineering

OSRAMOpto Semiconductors GmbH

Regensburg,Germany

Abstract— In the last years,multi chip on board LEDs became state-of-the-art to generate low beam and highbeam systems. These systems often consist of one light source and one singleoptics system. On top, recent LED development enabled multi chip SMT LEDs inthese systems. Alternative approaches use an assembly of several chips size SMTLEDs to create a single light source. The latter method offers the possibilityto create light sources more flexibly than with fixed multi chip devices. Inthese compound light sources the single LEDs are placed close together. The compoundlight sources can draw upon existing optical concepts usually used with multichip LEDs to accomplish low beam and high beam function with a single opticalsystem.

Besidedifferences of processing of afore mentioned systems also differences in theoptics design need to be considered. Due to the different structure of themulti chip and the compound light source optical differences already occur onlight source level.

Onone hand side, the mean luminance of both light source types is different. Thiswill be evaluated theoretically, by simulation and confirmed by exemplary measurement.

Onthe other hand, due to the dark gaps between the individual LEDs of thecompound light source, higher efforts are necessary to achieve homogeneousluminous intensity distribution. This leads typically to smaller luminousintensities that can be compensated for if the size of the optical system isenlarged compared to a system with multi chip LED light source.

Thisdependence of luminous intensity and size of the optical system in connectionwith the different light source types is analyzed in detail. Theoreticalconsiderations and simulation results will show the impact on size andperformance of a headlamp system if a compound light source or a multi chip LEDis used. (Abstract)

Keywords-LED;automotive lightging; multichip; SMD; SMT;Optics design; luminace; forwardlighting