One of the buzz phrases amongst European OEMs at the moment is Advanced (or Adaptive) Front-lighting System (AFS) in which the key parameters are road run, road type, weather conditions, and driver requirements. The objective is to provide the driver with the best possible visibility by varying the light distribution over time without dazzling oncoming traffic. Those with good memories may recall the Citroen that had the headlights that followed the front wheels as they turned left or right. A great idea, but no other manufacturer thought it worthwhile pursuing. The final nail in the concept’s coffin was legislation that required headlamps to be fixed in the straight-ahead position on cars.
The lighting components on a car are governed by stringent international standards: ECE in Europe and Japan and FMVSS in the U.S. However, in a move that sees legislation finally catching up with technology, they are about to be swept away, thereby removing the constraints that have been placed on car designers and engineers for years. “In 2003, we expect to have a more general allowance for swivelling beams,” says Wolfgang Hendrischk, head of headlamp development at Hella, “and from around 2005 we expect full AFS legislation. This will allow us to change the car’s light distribution according to whether it is in a town with good street lights, going along unlit roads cross country or on a freeway.”
Research is currently under way to assess the best methods of distributing the forward lights once it is permitted. The old Citroen method, though, is not thought necessarily to provide the best answer. “We think that swivelling both headlights may be a little bit too dramatic for some situations,” says Hendrischk, “so the other alternative is keep one of the lamps steady and just swivel the in-board one. A compromise between those would be to swivel both but at different angles—the in-board one swivelling into a wider angle and a little less on the outboard one. However, Hella has several AFS projects on its hands so we are quite happy if everybody has a slightly different approach about its use.”
“The first requirement designers and engineers are faced with when designing an adaptive headlamp system is ‘variability’—in other words, taking visible changes during operation into account,” says Dr. Wolfgang Huhn, head of lighting and switch development at Audi. “The impressions evoked by the dynamic changes in the headlamps at the front of a vehicle are just as striking as the changing expressions of a human face due to eye movement. If the focus is on technical aspects to the exclusion of all else, the automobile may seem to take on a menacing aspect. This is why Audi integrates design and technology, but also takes psychology into account, as well. All possible states and transitions between the positions are evaluated and finalised not only by engineers and designers, but also by psychologists and potential customers.”
A further function of the future is increasing the headlamp levelling at higher speeds. If the vehicle is on a freeway, it will be possible to give the driver a better view without causing glare. The next stage envisaged will be additional scope for moving the dipped beam while the longer-term aim is to provide variable-shape light distribution. “In this way,” says Dr. Huhn, “various implementations of the light-dark boundary will be possible and so the light functions for urban roads, country roads and freeways.”
The use of video systems to determine the run and width of the road or the use of navigation systems are other ways of enhancing the potential of AFS. If the run of the road is known in advance, the light distribution can be adapted beforehand. The intention is to let the light guide the driver’s gaze into a curve. The evaluation of the video images will not only make it possible to predict the further run of the road but also predict the position of other vehicles. However, some of the challenges still to be confronted are the robustness of the equipment, the limited aperture angle of the camera and the camera technology itself.
There are also open questions relating to the human aspects of the cornering functions problem, says Dr. Huhn. “When and in what direction should the dip beam be swivelled?” he asks. “What is the optimum relationship between the radius of curvature and the slew angle? Do both or only one of the headlamps need to be swivelled into the curve? To answer these questions, Audi is undertaking extensive trials involving test persons. A specially equipped vehicle makes it possible to vary the various light-specific and control-specific parameters in a precise way.”
While attention has been focused on the front lights of the car, it has not been at the expense of the rear lights. “Rear lights allow the driver to communicate with the driver behind,” says Dr. Huhn. “These signals must, therefore, be clear and easy to see without being annoying or even a nuisance. There is, of course, a range of regulations that rear lighting has to meet. On the other hand, rear lighting is a key design feature of a vehicle. This defines the boundary conditions for future technical solutions and optical design.”
Audi has set itself the target of making rear fog lamps obsolescent in the foreseeable future. “The brightness of an adaptive tail light of this kind will be tailored to the prevailing conditions and replace the rear fog lamp,” says Dr. Huhn. “The light intensity will be highest for fog or spray and lowest for high visibility at night.” The basis for this innovation is LED rear-light technology. By, for example, pulse-width modulating the power supply, the luminance of LEDs can be easily varied over a wide range.
Another field of development is integrating contamination and visibility sensors in the headlamp. “This headlamp should be able to detect fog, spray, rain and snow, contamination on the lamp window and even the separation and speed of following traffic,” says Dr. Huhn. “Using this data in conjunction with the vehicle data, it will be possible to adapt light output from the rear of the vehicle intelligently.”
Design, currently static with the emphasis on the non-illuminated state, says Dr Huhn, can in the future be defined by, and make use of, the variable shapes and brightness that the new vistas opened up by what LED matrices offer. “Software-driven design of this kind will even make it possible to provide variants for different models. Changes could be made with a software upgrade. What all rear-light variants have in common is a large, easily seen brake light. If multi-coloured LEDs are used, variations on the red functions, the flashing light and the reverse light would be possible.”