Today, LEDsÂ are increasingly being used as light sources for signal functions at the front of the vehicle as well. This trend will increase considerably in the coming years. The first full-LED headlamps, which also produce low beam and high beam, will be on the market in 2008. They open up new, far-reaching styling options and therefore great differentiation potential for automakers.
LEDs that produce white LED have been around for at least six years. The first applications in the front-end area were for position light and daytime running light. The rapid development of their performance now makes LEDs usable for low beam and high beam as well. In relation to this, the light colour of the white LEDs (colour temperature 5,500 K) is much closer to that of daylight ( 6,000K)Â than that of xenon light (approx. 4,000 K) and is close to what the human eye is accustomed to seeing.
The car driver does not tire as quickly and drives in a more relaxed manner their luminous efficiency is increasing rapidly: It is more than 40 lumen per watt today (lm/W), and there are already prototypes in research laboratories with approximately 130 lm/W (Luminous efficiency of Xenon light is 90 lm/W and Halogen light is 20 lm/W).
LED headlamps have a modular design
As high luminous power is required for low beam and high beam, Hella chooses multi-chip LEDs in the case of the LED headlamp. Special chip arrangements and housing geometries make it possible to produce the cut-off line without additional mechanical shading. As a result, compact headlamp systems can be realized. The light distribution is set up in a quasi-modular manner. The different light distributions are produced by means of differed optical modules that are matched to one another. Variation possibilities with regard to the arrangement and number of the modules open up new, far-reaching styling options and therefore great differentiation potential for automakers.In accordance with this principle, Hella has realized a full-LED headlamp prototype from different transmissive optical elements. The low beam is produced by six optical units. Three further units are added for high beam, a special module is sufficient for low beam. Daytime running light/position light and direction indicator with LEDs complete the full-LED headlamp, which, in the case of low beam, is already very close to the xenon values.
With reference to the number and performance of the LEDs, these and other prototypes are designed in such a way that in the year 2008, luminous power similar to that of a xenon headlamp can be achieved. In the course of this, the Hella lighting specialists take into account the performance of the white LEDs to be expected by then. This performance is increasing continuously.Hella is working with LED arrays (assemblies) as light sources for future headlamps. They consist of several individually addressable LED chips, which are arranged on a carrier substrate in accordance with a pre-defined pattern. The individual chips are triggered by means of pulse width modulation. This allows, on the one hand, the switching-on and switching-off of individual LED chips and therefore the generation of different cut-off lines, and, on the other hand, an intensity modulation in the light distribution. In addition to the mechanism-free implementation of intelligent AFS lighting functions,Â the LED arrays allow, in conjunction with forward-looking vehicle sensor technology and intelligent triggering electronics, the realization of active lighting functions such as marker light or glare-free high beam.