Over the last decade, changes in automotive lighting have been confined to a few main technologies - the use of High Intensity Discharge (HID) and Light Emitting Diode (LED) light sources. In addition, free-form reflectors and projector-style headlight designs have been developed.
However, the scene is now set for some major changes in the next 2-3 years, with companies planning the introduction of active systems that alter headlight beam spread and range on the basis of road type and vehicle speed, variable intensity rear lights that completely remove the need for separate switchable foglights, and interior lighting that alters to match environmental and driving conditions. In addition, night vision systems incorporating laser and other technologies are likely to make an impact.
Adaptable Front Lighting
Headlights that automatically adjust to match the driving conditions have long remained an engineering dream. Despite the use many years ago by Citroen of headlights that turned with the steering wheel, no other manufacturer has since taken up the challenge. However, this is very likely to change in the next few years with the introduction of the Audi Advanced Front-Lighting System (AFS).
Audi's AFS is expected by the company to be introduced on 2003 models - it should revolutionise night safety. One function that cars equipped with the system will have is the ability to illuminate around corners, in some cases even before the corner is reached! The system uses a number of inputs, which vary with the situation being encountered.
- Side illumination when cornering - or when crossroads are arrived at - is determined primarily by steering angle.
- The activation of the cornering light function also depends on the speed at which the vehicle is travelling; Audi has decided that at motorway speeds cornering illumination isn't as important as at slower speeds where sharper changes in direction are undertaken.
- The indicator signal can be used to provide early warning as to the direction in which the driver intends to turn. On the basis of other inputs (such as vehicle speed) the appropriate radius of corner that the vehicle is to traverse can be estimated. (For example, a driver slowing down from 60 to 20 km/h and indicating a right-hand turn is probably about to negotiate a junction where the radius of curvature will be small.)
- A "look ahead' cornering function can be supported by the navigation system. In addition to predicting the tightness of the bend about to be negotiated, data from the nav 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 into best deciding headlight range and when side lighting should be used, eg to illuminate crossroads.
- Signals from light and rain sensors can be used to allow the switching on of bad-weather lights or the reducing of glare from wet roads.
Cars fitted with HID headlights already use sophisticated headlight levelling techniques in order that they not dazzle oncoming drivers, but active headlight levelling of both the high and the low beams is likely to become more widespread. In addition, Audi expect to introduce a variable light distribution function, where the shape of the low and high beams will alter, depending on the type of road that is being driven. 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.
In addition to vehicle speed and navigation inputs being used to determine the type of road, video camera systems that monitor the presence of other traffic and precisely measure the width of the road can also be used. If the left-hand edge of the road can be determined accurately, for example, the shape and spread of the beam can be tailored to illuminate it.
However, AFS is still in development. Questions that remain to be answered include:
- When and in what direction should the dipped beam be swivelled?
- What is the best relationship between the radius of curvature and the slew angle?
- Do both or only one of the headlights need to be swivelled into the curve?
It should be noted that in luxury cars - in which the systems will be first introduced - nearly all of the input sensors already exist: road speed, navigation, ambient light and of course indicator function. Importantly, one potential stumbling block seen by Audi is that current legislation and automotive design standards are not keeping up with the technology - many of the functions mentioned above are currently not legal!
Intelligent Rear Lighting
While developing an active headlight system is quite complex, making the rear lights intelligent is much easier. The frequently forgotten or misused rear foglights, for example, can be almost immediately replaced with taillights that vary in their intensity, depending on the atmospheric conditions. The light intensity will be highest for daylight fog or spray and lowest in clear night conditions. Sensors built into the lights can be used to detect environmental conditions, contamination (eg dirt) on 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 LEDs, the tail lights' intensity can be easily and cheaply varied over a wide range, using pulse width modulation techniques. Typically, three times as much current is needed to provide adequate day-time illumination as at night.
Another intelligent technology is the flashing of the hazard lights (ie all indicators working simultaneously) after emergency braking has been detected. By using inputs from the ABS, the time before the vehicle is completely stopped can be calculated, and the hazard lights switched on as the car draws to a stop.
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. So the brake light can be a different shape, depending on whether it is being used simultaneously with the reversing lights or alone, for example.
Finally, the rear numberplate can be illuminated from behind by means of electro-luminescent (EL) foils. DaimlerChrysler is experimenting with fine electro-luminescent foil applied behind the numbers, which are placed on a transparent material. This produces an evenly bright and clearly visible illuminated surface. In addition, the transparent foil on which the registration number is printed features a special coating that also reflects the light from the headlamps of following vehicles.
Interior Lighting
When you consider it, interior lighting in cars remains very primitive - the illumination of the instruments and controls varied with just a manual brightness control, and the rest of the cabin lit with only a couple of discrete lights. With less legal impediments standing in the way, changes in this area may occur very quickly.
In addition to the introduction of coloured LEDs, EL foils can be used to provide uniform and glare-free lighting. Already used in the interiors of aircraft, EL foils are suitable for highlighting contours or uniformly illuminating strips. 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-cabin 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.
Laser Vision
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. DaimlerChrysler has been trialing such systems in commercial vehicles, and are now moving to normal cars for further testing.
Other night vision systems being developed simply detect the heat energy given off by living objects - excellent for spotting the pedestrian but not so good for seeing a sign that has fallen across the road. The DaimlerChrysler Active Night Vision system instead illuminates the road ahead by the use of infrared lasers built into the car headlights. 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 energy is invisible to oncoming drivers, the beams can be aimed much higher, helping to give the system a range nearly four times that of conventional low-beam headlights. A digital camera records the illuminated image, projecting it onto a dashboard-mounted LCD or heads-up display.
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 that the camera is subjected to. The laser is pulsed 30 times per second, with each pulse being 8 milliseconds 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, the recording of other light sources is minimised.
Ah, 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 just 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!
Conclusion
While some of these technologies will remain expensive and so be confined to luxury and other costly cars, other technologies can be introduced very cheaply immediately. Intelligent, variable intensity tail-lights and more sophisticated cabin lighting are two that you can expect to see in production very shortly. The intelligent taillight is also a technology that would be relatively straightforward to introduce as an aftermarket retro-fit, too....
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