Halogen, xenon and incandescent bulbs used for automotive headlamp applications have high brightness filaments with precise geometry. On the other hand the energy efficiency as well as the lifetime is significantly lower compared to other light source technologies, especially LED technology.
Incandescent bulbs that are used for automotive signaling lamps have less brightness and the tolerances of the geometry are less critical. However due to the limited lifetime, it is of interest to make used of LED technology for signaling lamps.
Currently LED's are available with brightness levels comparable or even significantly higher compared to automotive halogen and incandescent bulbs. While LED's emit only in one half of the sphere, the coil of an halogen and incandescent bulb emits in the complete hemisphere. Thus the headlamp optic developed for filament bulbs does not fit to the emission pattern of a single LED. Multiple high brightness LED's have to be arranged in such geometry that the emission pattern as well as the geometry resembles the corresponding emission pattern and geometry of a filament bulb and makes efficient use of the existing automotive optical components.
U.S. 2010/0244649 A1 discloses a LED lamp unit for automotive lamps in which two LED's are mounted at two opposing sides of a common mounting plate to emit in opposed half spaces. The mounting plate is thermally connected at one side to a heat sink comprising several cooling fins. A fan is arranged at the backside of the heat sink to generate a forced air cooling of the heat sink. In the proposed automotive lamp, the two LED's are arranged inside of the volume surrounded by the reflector of the lamp whereas the large heat sink and the fan are arranged outside. Such a lamp unit requires a different construction of the lamp compared with the known constructions using halogen and incandescent bulbs.