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.
LED technology offers new opportunities for the future concerning styling, technology and energy consumption.

Advantages of LEDs

LEDs especially stand out for the following characteristics:

- the light temperature of the LEDs nearly achieve daylight quality
-  an extremely high lifetime lasting more than a whole vehicle life
- a significantly lower energy consumption
- more effective opportunities for the use of installation space in   headlamps
- unique freedom and variety in styling for the development of brand   characteristic styling elements within headlamps

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.
Due to their small sizes, LEDs offer the opportunity to combine both light systems for the first time.

Detailed information concerning light technology within the Audi R8 Full-LED headlamp can be found here. (at the moment only available in German)

Temperature management

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.
To protect the hottest part, the chip, cooling elements with a controlled air transportation system have been developed. The systematic direction of the warm air to the bezel of the headlamp is so simultaneously being used for de-icing and decondensation.

Reduction of energy consumption

The application of LED technology significantly contributes to the avoidance of CO2 emission and the reduction of fuel consumption.
This aspect especially gains importance with the implementation of daytime running light (DRL). DRL with LED needs 14W of energy, whereas the use of conventional vehicle lighting at day (low beam, rear lights, position lights) consumes 300W.

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)

                  Reflection system

                  Projection system

           Temperature management