The Item of this paper is perceptibility (being seen) only. It does not deal with quality of light distributions of headlamps (seeing).
Vehicles are (like everything else) perceptible because of their contrast to the ambience. This contrast depends on many parameters like e.g. colour of vehicle and ambience, colour distribution, relative luminances, luminance distribution, and so on. It is of mayor importance for the person who perceives a vehicle that he recognises if the vehicle is moving or not. The person can decide most of his next actions in traffic out of this basic information.
So the first fundamental demand on vehicle lighting is to show always clearly that a vehicle is present and if it is moving or not.
The next level of importance is the indication of the intention of the driver. Using the lighting devices of a vehicle is one of the few possibilities to communicate with the environment. The better the driver uses it and the better the signal quality, the clearer the communication. Information is e.g. the indication of turning, braking, reversing but also â€œleave my laneâ€, â€œI am parking wrong and I knowâ€, â€œThanks for giving wayâ€ and so on. Some would say this is misuse, but beyond doubt it is communication.
The second fundamental demand on vehicle lighting is to allow for clear communication with other road users.
A mayor improvement of the perceptability of cars during daytime can be reached with light because contrast to the ambience and luminance of the object (car, motorbike) are the crucial factors for conspicuity.
Today the illuminated surface of new headlamps varies roughly 1:10 (Low Beam Amin1 ï‚» 30 cmÂ² und Amax2 ï‚» 300 cmÂ² ). The luminances Imax1 / Imax2 are less different, about 1:2 , the illuminaces Emax1 / Emax2 on the observers eye are roughly the same 1:2 in static cruising condition (no acceleration or deceleration). A bigger bright surface is more conspicuous than a smaller one of the same brightness. This leads to the implication that cars and especially motorbikes with bigger headlamp surfaces are better detectable in bright ambience than with smaller ones.
Special Daytime Running Lights (DRL) improve again the situation. The minimum surface allowed of DRL is ADRLmin = 40 cmÂ² today. The luminous intensity is 400 cd ï‚£ IDRL ï‚£ 800 cd in Europe. In USA the max value is up to 3000 cd. DRL is operating when the engine is running or at least signal 15 is on.
The ideal solution to improve perceptability of cars in traffic is the usage of DRL with LEDs as light source. Longest lifetime, low energy consumption and higher luminous intensities combined with a very conspicuous colour. The colour temperature is about 5500K and much higher than incandescent lampÂ´s colour temperature. The different spectral distribution (compared with a Plank radiator) multiplies the effect of conspicuity. The mandatory position lamps can be easily integrated into the DRL. The luminous intensity of the DRL could be controlled e.g. by pulse-width-modulation of the supply voltage to create a position lamp.
In 2007 or 2008 the first full LED headlamps will be introduced into the traffic. The low beam will be excited by 6 to 12 LEDs in all probability. The added lit surface is similar to a mid size to big standard low beam headlamp. The conspicuity of a car with LED headlamps is by the mentioned reasons higher than the conspicuity of a car with halogen and Xenon headlamps.
Next priority is the direction indicator. Single cars are equipped with LED direction indicators. The available LEDs are much too expensive and the technical characteristics like e.g. lumen output and colour stability are poor. A lot of additional complexity has to be handled. The direction indicating signal without any visible time lag produced by LED is the benefit for the big effort. Switching on and off is highly conspicous and perceptable. The biggest benefit occurs in the case of hazard warning. The alertness of oncoming or following drivers is clearly higher than with standard systems.
An Intelligent Rear Light, which was presented at the SIA conference VISION 2002, is based on LED tail lamps. Other additional benefits may follow.
Dr.-Ing. Wolfgang Huhn, Audi Electric/Electronic, General Manager Lighting and Switches Development, Ingolstadt, Germany.
1981 â€“ 1986 Studies at Darmstadt University of Technology, Electro-Mechanics and Lighting Technology. Doctors Degree 1999 (Doctoral Thesis Supervisor Prof. Schmidt-Clausen)
1987 â€“ 2000 BMW Munich, Responsibilities in chronological order: Pre-Development Lighting, Head of Lighting Development, Electro-Mechanics Small Platform, Head of Assembly-Planning E/E.
2000 â€“ 2004 AUDI AG Ingolstadt, Head of Lighting and Switches Development.