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Automotive lighting systems are about to undergo a revolution, from headlights that “see” around corners to tail-lights that vary according to the braking intensity. But that’s not all – some important new safety features are in the pipeline as well. By JULIAN EDGAR Automotive lighting is undergoing a revolution. Not only are High Intensity Discharge (HID) and Light Emitting Diode (LED) light sources now being widely used but car lighting systems are also becoming increasingly intelligent. This “intelligence” ranges from headlights that swivel to “see” around corners to brake lights that illuminate by varying degrees, depending on how quickly the car is slowing. Additionally, interior lighting is now being viewed by designers as having an important impact on the interior ambience of a car and so is being given 66  Silicon Chip the attention previously reserved for picking interior trim specifications. Active headlights While some Citroen models of decades ago used swivelling headlights, such an approach never became popular. However, headlights that actively move their illumination patterns are now being revisited – and the technologies being employed are far more sophisticated than ever before. Audi’s Advanced Front-Lighting System (AFS) is one approach and is expected to be introduced into production vehicles in the near future – in fact the most basic version of the system (cornering illumination) is already present on the Audi A8 luxury model, as well as on some other cars. However, the proposed systems are even more interesting - they will have the ability to start “shining” around corners even before the car begins its turn! In the Audi system, the amount of side illumination that occurs when cornering is mainly determined by the steering angle. However, it also depends on the vehicle’s speed. For example, Audi has decided that at motorway speeds, cornering illumination isn’t as important as at slower speeds where sharper changes in direction are undertaken. In addition, the turn indicators are also used to provide an early warning as to the driver’s intentions. By then adding in speed information, the appropriate radius of the corner that the vehicle is about to negotiate can also be estimated. For example, a driver slowing down from 60km/h to 20km/h and indicating a righthand turn is probably about to negotiate a junction www.siliconchip.com.au with a small radius of curvature and so the headlights’ illumination can be directed accordingly. A “look ahead” cornering function can also be supported by the GPS navigation system. In addition to predicting the radius of the bend about to be negotiated, data from the navigation system can also be used to categorise the type of road that the car is moving along. This can be used as an additional input for deciding headlight range and when side lighting should be used; eg, to illuminate crossroads. Signals from light and rain sensors can also be used to switch on bad-weather lights or to produce a lighting pattern that reduces glare from wet roads. As the final step in the implementation of these systems, Audi expects to introduce a variable light distribution function, where the shape of the low and high beams alters depending on the type of road. A low beam that automatically spreads when the car reaches junctions, increases in reach on country roads when there is no traffic coming the other way, and “looks” around corners can all be achieved. It should be noted that in luxury cars (in which these systems will first appear), nearly all of the input sensors already exist for this sophisticated approach to vehicle lighting – road speed, navigation, ambient light and, of course, the turn indicator function. The DaimlerChrysler system While Audi has already introduced cornering lighting and are well advanced in their plans for actively moving headlight illumination patterns, DaimlerChrysler expect to launch mechanically moving headlights with-in 12 months. Developed in conjunction with Hella, the system will feature headlights that follow the driver’s steering movements, swivelling in the corresponding direction as the vehicle enters a curve. But just how beneficial would this be to night driving vision? Daimler­ Chrysler claims that when entering a curve with a radius of 190 metres, conventional dipped headlights are able to provide illumination for a distance of only 30 metres. By contrast, the corresponding distance for swivelling headlights is 55 metres! The DaimlerChrysler active lighting system uses the HID headlight www.siliconchip.com.au Head-lighting with cornering function Cornering function Dipped head-lighting Swivel dipped head-lighting Cornering function Swivel dipped head-lighting Variable head-lighting Country road lighting Motorway lighting Cornering function Urban lighting Audi’s Advanced Front-Lighting System shows the approaches likely to be introduced over the next two years. From top to bottom: (1) cornering lighting which responds to steering lock and speed inputs; (2) headlights that swivel to illuminate around corners; (3) headlight beams that actively change shape depending on the driving environment. (Audi) technology already widely used in Mercedes models. Electric motors are used to swivel each headlight, with the individual controlling microcomputers supplied with real-time information from the steering-angle and speed sensors. In addition, conventional (for HID lights!) active headlight levelling is used to reduce the chance of dazzling oncoming drivers. US automotive parts manufacturer Valeo is also working on a similar system, which they have dubbed “Bending Light”. Like the Daimler­ Chrysler system, Bending Light uses motorised headlights which swivel at angles determined by using inputs from the steering wheel angle, wheel speed sensors and (optionally) a GPS system. However, German auto-maker BMW is developing a headlight system that is even more sophisticated. Their socalled “pixel headlights” use 480,000 individually-controlled and microscopically-sized mirrors to take over the reflector function. This approach allows the headlights’ beam patterns to be precisely tailored to the driving conditions, allowing dazzle-free perSeptember 2003  67 indicating a left-turn by replicating a left-turn arrow as part of the headlight beam. One interesting potential stumbling block to the introduction of some aspects of these breakthrough headlight systems is legislation – many of the functions mentioned above are illegal in many countries! Rear lighting Headlights which automatically change their beam width, angle and reach are all possible when inputs to the system include GPS. With nearly all luxury cars sold today fitted with integrated GPS navigation systems, such an approach is quite feasible. The safety benefits of this type of system would be enormous. (Audi) The BMW pixel light system, which is an ongoing research program of the German car maker, uses 480,000 individually-controlled microscopic mirrors in place of a conventional reflector. The shape of the beam is completely programmable. (BMW) manent high-beam illumination. It also allows specific headlight illumination patterns for bends, city environments, motorways and bad weather. Additionally, road lane markings can be illuminated with their own sub-beams. BMW also somewhat bizarrely suggest that navigation instructions could be given to the driver by means of altering the pattern of lighting – eg, 68  Silicon Chip While not quite as startling as headlight development, rear lights are also undergoing major changes. One area of development is in “intelligence” – making the rear lights automatically do what is required of them to improve their primary function of communicating with other road users. For example, the frequently forgotten or misused rear foglights can be almost immediately replaced with tail lights that vary in their intensity, depending on weather conditions. The light intensity will be highest for daylight fog or spray and lowest in clear night conditions. Sensors built into the lights could be used to detect environmental conditions, contamination (eg, dirt) on the lenses and even the speed and separation of following traffic. The latter input can be used to decrease the brightness of rear lights working in “fog mode” as approaching traffic draws near. By using pulse width modulated LEDs, the tail lights’ intensity can be easily and cheaply varied over a wide range. Typically, three times as much current is needed to provide adequate daytime illumination as at night. Another intelligent technology is automatically flashing the hazard lights (ie, all indicators working simultaneously) after emergency braking has been detected (some cars already do this if an airbag deployment has been detected). The currently clearly-defined shape of rear lights may also no longer continue. If matrices of LEDs are used to form the rear lights, their shape can be dictated by software commands, changing depending on the function being enacted (eg, brake light or indicator, or both) and even from model to model. The brake light can therefore vary in shape, depending on whether it is being used simultaneously with the reversing lights or alone, for example. Finally, the surface area of a brake This diagram shows how swivelling headlights can dramatically extend the range of night vision. In this example, conventional dipped headlights are able to provide illumination for a distance of 30 metres in a curve with a radius of 190 metres; swivelling headlights add another 25 metres of range! (Daimler­ Chrysler) light that illuminates can be dictated by how fast the vehicle is slowing. BMW’s concept car X-Coupe has brake lights in which only the outer rings illuminate under gentle braking. However, as the pedal pressure increases, the illumination spreads inwards until, under full braking, the entire area is illuminated. Interior lighting When you consider it, interior lighting in cars remains very primitive – the illumination of the instruments and controls is usually varied using just a manual brightness control, while the rest of the cabin is lit using only a couple of discrete lights. However, with less legal impediments standing in the way, changes in this area could occur very quickly. In addition to the introduction of coloured LEDs, electroluminescent (EL) foils can be used to provide uniwww.siliconchip.com.au By using matrices of LEDs, the shape of the tail-light and its brightness can be altered depending on the function it is performing. This approach also allows model-to-model styling variations, software-driven changes from day to night and the use of a large and easy to see brakelight on all models. (Audi) form, glare-free lighting. Already used in the interiors of aircraft, EL foils are suitable for highlighting contours or uniformly illuminating strips. (EL foils are driven by an AC supply, meaning that some form of ballast is required – which in turn may have associated electromagnetic compatibility issues). Fibre-optic light pipes are also starting to make inroads into cabin illumination – for example, the technology is ideally suited to illuminating from within the shift pattern on a gearknob. The psychological aspects of in-cab- in illumination are also being considered. For example, Audi suggest that at night and in dark environments, the interior lighting should create a perception of space, “so producing a feeling of well-being”. When the car draws to a stop at night and the driver moves to leave the vehicle, EL strips could dimly illuminate the shape of the inner door, providing the same visual cues normally used when exiting in daylight. Such a “psychological” approach is already being taken on the Mercedes Arrays of red LEDs are already being used in the brakelights of a number of cars. Their lower current consumption, faster illumination time and greater longevity gives them major advantages over traditional incandescent lamps. This is the rear light assembly of a current Mercedes SL-Class. (DaimlerChrysler) www.siliconchip.com.au SL-Class. The interior of this car uses: • Illuminated driver and passenger footwells, generating “a pleasant sensation of spaciousness”; • Night lights in the door handle recesses that light up the border indirectly, helping passengers to open the doors in the dark; and • A lamp integrated into the housing of the rear vision mirror which casts a gentle light over the centre console. To conserve energy (and to ensure that the right mood is created), a special sensor in the SL-Class detects The BMW 5-Series brakelight design uses high-intensity LEDs that shine into optical tubes that stretch around the rear lights. (BMW) September 2003  69 Laser Vision: Using Infrared To Overcome The Glare In this prototype DaimlerChrysler system, small ancillary infrared-laser headlights illuminate the road ahead of the car. A video camera relays the image to a dashboard LCD screen which the driver can view. The infrared light is invisible to oncoming drivers, so the beams can be aimed much higher than would be the case with visible light. (DaimlerChrysler) This graphic clearly shows how the infrared beam can be aimed much higher than conventional lights. Tricky time-referenced pulsing is used so that if the oncoming car is equipped with the same system, its video camera isn’t blinded. (DaimlerChrysler) A limiting factor in all forward night vision is the capability of the human eye to distinguish objects, especially when being subjected to the glare of oncoming vehicles. However, if a quick check of a dashboard LCD screen could be made to see if that glimpsed pedestrian really is about to step off the edge of the footpath in front of the car, safety would be substantially improved. At least one company, Daimler­ Chrysler, is testing such a system. Four additional small infrared-laser headlights, a video camera mounted on the roof and an LCD screen mounted in the instrument panel comprise the visible parts of the system. Each laser is only pinhead in size and is matched with a special diffuser lens that ensures a wide, evenly distributed cone of infrared light. Because the infrared 70  Silicon Chip This simulation shows how a pedestrian, normally invisible behind the glare of an oncoming car, can be clearly seen with the infrared laser system. (Daimler-Chrysler) energy is invisible to oncoming drivers, the beams can be aimed much higher, helping to give the system a range that’s nearly four times that of conventional low-beam headlights. Another benefit of using a narrow-band infrared light source is that filters can be used over the video camera lens to reduce the glare of oncoming headlights. In fact, the blinding effect of these lights can be decreased by a factor of 50–100, while still allowing the reflected laser light to pass. In addition to this filtering technique, another approach is used to reduce the glare to which the camera is subjected. This involves pulsing the laser at 30 times per second, with each pulse being 8ms long. The video camera’s shutter is tied to this pulse rate and with each dark period lasting three times as long as the bright period, interference from other light sources is minimised. But what if the laser-light car meets another coming the other way? Won’t the pulsing of the other car’s laser system then have the wrong affect? Incredibly, the system takes this into account. Using precise time reference and compass direction signal inputs, the laser output pulsing is configured so that cars travelling in opposite directions have their laser pulses separated as widely as possible! The DaimlerChrysler system is thus fundamentally different to other night vision systems that simply detect the heat energy given off by living objects. One big advantage of this system is that it can detect obstructions on the road that are at the same temperature as their surroundings. www.siliconchip.com.au Front interior light Centre-console illumination Interior door-handle illumination Reading light Rear interior light Footwell illumination Centre-console illumination Reading light Outdoor lighting Door trim illumination Entry illumination Active rear reflector Door pocket illumination Footwell illumination Door-handle illumination Interior lighting is becoming increasingly sophisticated as car makers strive to create the right psychological signals for relaxed night-time travelling, in addition to providing the basic required illumination. This Audi A8 has illumination of the door pockets, door handles (inside and out), door trims, footwells and the ground beneath the open doors – in addition to the normal instrument, controls and cabin lights! (Audi) Mercedes and Volvo vehicles are now being fitted with exterior entrance and exit lighting, switched on when the car is unlocked by the remote. This is a very effective approach and given that it costs little to integrate a light source into the underside of the rear vision mirrors, can be expected to be adopted by other makers. (DaimlerChrysler) ambient light levels, the electronic control module then using this input to determine the illumination intensity of the various interior lights. In summary, the future for car lighting looks exciting. Intelligent front www.siliconchip.com.au side-lighting, variable intensity taillights and more sophisticated cabin lighting are just three new automotive lighting technologies that you can expect to see on production cars in SC the near future. DaimlerChrysler has almost standardised on the use of LEDs mounted in the rear vision mirrors for the side repeater indicators. The wraparound design allows both front and side recognition. (DaimlerChrysler) September 2003  71