LED in headlamps
In rear lamps, applications with red and yellow LEDs already are state of the art in lighting technology. In headlamps, especially white LEDs are necessary that for main functions must provide a better light performance. White LEDs have already been used for signal functions like position or daytime running light in some serial projects. With the development of the first Full-LED headlamp for Audi R8, Automotive Lighting set up a world premiere. For the first time, all light functions of a serial headlamp are being realized in LED technology, these are low and high beam, daytime running light, turn indicator and position light.
Advantages of LEDs
LEDs especially stand out for the following characteristics:
Function of LEDs
LEDs are based on semiconductor technology. The light is emitted directly out of the semiconductor substrate when a forward voltage is applied. The colour depends on the band-gap energy of valence and conduction band for the materials forming the semiconductor. The amber colour is directly generated by the LED by Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material. Through the luminescence conversion process, white light is generated. A blue diode in combination with an applied converter material, the colour blue and yellow, the combination of which is perceived as white light.
Technical implementation in headlamps
To achieve the targeted light patterns with LED applications in headlamps, two conventional opportunities are available that are already implemented in filament and also in gas discharge lamps. Either the light of the LED is redirected through a reflector in order to achieve the light pattern on the road. Or, alternatively compact systems can be applied that project the light in the street using a lens.
In contrast to Halogen or Xenon systems, LEDs emit "cold" light meaning that no infrared radiation is being produced. Due to the high efficiency, 20% of the input energy are transformed into visible light (for comparison a filament bulb only transforms 5%) - the rest of the energy generates heat within the semiconductor chip. Luminous flux, colour and forward voltage are dependant on the temperature. As soon as the allowed temperature is exceeded, the lifetime of the LED will be badly affected or in worst case will be destroyed.
Reduction of energy consumption
The application of LED technology significantly contributes to the avoidance of CO2 emission and the reduction of fuel consumption.
Outlook and trend
LED technology within the external vehicle lighting is still in its infancy. Future fields of activity are to be found especially in the implementation of adaptive light systems and in the further optimization of energy consumption.
Full-LED headlamp of Audi R8
Styling freedom for LED applications in headlamps
enabling a brand characteristic appearance of every headlamp
Design of a LED module
Further information for LED technology in headlamps can be found here. (at the moment only available in German)