Low energy consumption, long lifetime, and opportunities to achieve greater efficiency and design flexibility—these are some of the main drivers behind the introduction of the first LED headlamps with main functions (low beam, high beam) over the past few years. The design of LED headlamps makes it possible to generate full advanced front-lighting system (AFS) functionality, such as dynamic bending or adverse weather light, without any mechanical means.
By using several LED modules and variation in current to generate specific light patterns, one is able to adapt the light distribution according to the needs. This includes the adaptive high beam or glare-free high beam, which will be realized in the near future, according to Dr. Rainer Neumann of Visteon Innovation & Technology GmbH.
Taking part in the Automotive Lighting Technology Conference on April 24 at the SAE 2012 World Congress in Detroit, Neumann will detail the opportunities with the introduction of LED light sources to combine the main functions with additional features in front lighting.
LEDs have already found more widespread use across vehicle segments for center high mount stop lamps (CHMSL), rear lamps with stop/tail functions, and even daytime running lights, for which the bright white light with higher color temperature than halogen or high-intensity-discharge (HID) bulbs generates a kind of signature light even during daytime. For the main functions of a headlamp—low and high beams—there are only a few vehicles today that use LED light sources.
The market for affordable solutions that can be offered in electric vehicles and smaller vehicle segments has not yet started, but a roadmap for headlamp trends indicates that the advantages of LEDs eventually will lead to mass production for the main functions. The use of LED light sources for low- and high-beam functions in all vehicle segments is strongly correlated to the availability of LED modules for these functions. Individual design solutions will be applied in the premium segment, but the realization of a reasonable market share (15% of all new vehicles in 2020) can only be achieved in light-source designs like the halogen and HID bulbs can offer today.
The advantage of LED chips in terms of light performance is defined in the high color temperature (5500 K), which generates a homogenous carpet of light. The use of LEDs also offers the chance to generate the low beam and high beam out of several chips, making it possible to design a variable light pattern by dimming and enhancing various regions of the distribution.
An example of such a layout is based on two reflectors used to implement the various functions. (Combined solutions between projector and reflector as well as projector-only solutions are also possible.) With projectors, one needs additional shutters to generate the cutoff line of the low beam. Reflectors can reach up to 65% efficiency by using complex surfaces, as with halogen bulbs (e.g., H7).
The use of a lot of LEDs with dimming factor is responsible to organize the glare-free effect. A camera is the basis of this system, which can detect the road users with corresponding light sources, distance, and speed. The calculation of the current position of the oncoming vehicle is the information needed to direct the light around these obstacles and avoid direct glare light.
The type of LED chips varies in size from 1 x 4 mm (0.04 x 0.16 in), 1 x 2 mm (0.04 x 0.08 in), and 1 x 3 mm (0.04 x 0.12 in). The chips are placed on a plate that can be mounted on an LED carrier containing the corresponding heat sink and will be a standard part for different kinds of LED chips. The design principle with this low-weight material (aluminum or magnesium) is to make a replaceable LED solution for future applications possible.
The use of a set of LED chips or arrays with individual switching phases, as well as the dimming factors and overlapping elements, leads to more flexibility to realize AFS and glare-free high-beam concepts. The major challenge will be to offer modularized parts of LED chips and carriers, as well as electronic-control elements. This step of future development has not yet started, as the LED chips are still under development and are changing periodically in their principal structure.
This phase will be finished in one to two years, according to announcements from light-source suppliers. Additionally, with modularization, there will be the chance to introduce LED front-lighting solutions in smaller vehicles and with improved light distributions in comparison to the traditional technologies.
Individualized solutions, mainly for the premium segments, will still be under development using nonstandardized LED chips and additional technologies such as light pipes and special design lenses.
This article is based on SAE International technical paper 2012-01-0264 by Dr. Rainer Neumann of Visteon Innovation & Technology GmbH.