Vehicle headlamps are among the last automotive lighting applications to successfully adopt LED technology. Compared to other lamps such as rear lights, brake lights, turn signals and Daytime Running Lamps (DRLs), headlamps have proved more difficult to realize. Although powerful white LEDs on the market today are able to provide sufficient brightness for use in main headlamp units, recent advances in thermal-management and LED assembly at the light-engine level have proved critical in enabling the latest generation of LED-based headlamps to enter production.
High-brightness white LEDs for use in headlamps promise several important advantages over current tungsten-halogen and xenon lamps. The light emitted is at a color temperature close to that of natural daylight, which can improve visibility for the driver. Moreover, the illumination pattern can be controlled accurately to prevent dazzling other drivers. In addition, given proper thermal management, reliability can be extremely high, allowing the lamp to last the lifetime of the vehicle.
An LED headlamp can also be much smaller than a conventional headlamp, giving greater freedom to car stylists, and innovative features can be built in such as selectable illumination patterns for various driving conditions. Finally, it is possible to produce all-in-one light units, which combine LED turn signal, DRL and headlamp high/low beam in a convenient sealed unit that can simplify vehicle assembly and repair.
Despite the many advantages LED headlamps have to offer, thermal design is critical to allow driving them at high current for optimum brightness while simultaneously ensuring reliability for the lifetime of the vehicle. This calls for careful choices with regard to material technologies, especially the substrate technology, as well as assembly techniques such as soldering, mechanical fixings, and thermal adhesives. Accurate and precise placement of light emitters during assembly is also required, to ensure correct optical alignment relative to the lenses and reflectors in the headlamp unit so as to maximize light output and directional control of the beam.