I have mentioned before that I am a fan of (and a subscriber to) the French language ‘Le Mans Racing’ magazine - and an article caught my eye in the most recent edition, that I thought might interest my readership here. It is all about the emergence of LED headlamp technology, and I translate (and paraphrase) it below:
It was well-publicised by Audi, praised by the drivers who used it and also criticised by GT drivers who spoke of being blinded, but LED headlights hit the headlines in the recent 24 hour of Le Mans. They also achieved an historic victory.
Since their invention, car headlights have always evolved - from traditional tungsten bulbs to halogen. In both cases though, the same principle is used - a filament (wire) in a glass bulb. For a few years, xenon headlights have become more widespread. The bulb consists of two electrodes sitting in xenon (a gas) under high pressure. An auxiliary system that generates a high voltage of 20,000 volts starts the illumination of the gap between the two electrodes; then the voltage is reduced to 85 volts as soon as the beam is started.
A few years ago LED headlights appeared in concept cars at shows and exhibitions, giving designers greater freedom - enabling them to design cars that did not have merely round headlamps. And this year, for the first time, LED headlights appeared in competition, fitted on certain cars in the 24 hours of Le Mans. LEDs (Light Emitting Diodes) consist of a semi-conductor which converts electric current directly into light, and a lens ensuring that the light forms a beam. One can also put a mirror behind the LED (like in a traditional headlight).
There are several advantages.
The delay to illuminate an LED is extremely short - between 2 and 10 milliseconds - this is especially useful when flashing headlights, compared to 150ms to 300ms for halogen lights.
Since about 80% of the energy is converted to light, compared to 20% for traditional bulbs (the rest is converted to heat), headlights with equal brightness consume much less current.
The temperature of the emitted light is 6000 Kelvin, which amounts to a very white light, comparable to daylight. This is identical to that produced by xenon headlights (but compares to only 3000K for halogen, which are slightly yellowish). But the light is more diffuse, less violent than xenon and the lighting is more “comfortable”, and permits better distinction of the features of the road. In fact, halogen headlights produce a luminosity of 1500 lumens, xenon bulbs about 3200 lumens and a headlight with 6 LEDs produces about 1500. The light produced is therefore less bright than xenon, and therefore induces less glare.
The additional weight of xenon lights is also an important consideration - the combination of the weight for the projection equipment and the bulb itself is around 1.1 - 1.2kg, compared to 650g for a headlight consisting of 9 diodes. The integration into the bodywork is also simpler: no big projector to install, less heat generated, a flexible and adaptable shape along with a reduced volume; and it is the last two reasons that are important in racing circles.
In summary, then, LEDs are light, easy to install, use a little less current than xenon and a lot less than halogen and produce a less violent and a slightly less glare-inducing light than xenon but more homogenous and comfortable than halogen.
Victory at Le Mans
Only three models of car - all LMP1 - were equipped with LED headlamps at this year’s 24 hours. Of course there were the three Audi R18’s and in addition two of the four Oak Pescarolos. The 2011 version of the Peugeot 908 had a mixed lighting system, with a single LED lamp situated above the more traditional xenon lights. Although the LEDs of Audi and Oak came from the same supplier (Osram), the installations were completely different on the two cars. The implementation on the Audi was specific to the R18. On each side of the car was a double vertical beam, with 5 diodes on the outside of the headlamp and three on the inside. Behind these diodes were placed many mini-reflectors. Only the outside part was illuminated during the daytime.
Oak Racing replaced the three traditional Xenon headlights on each side of their Pescarolos by three LED
projectors, supplied by the RaceTech Harnessing. One of these had six diodes, and the other two had just three, all equipped with lenses to focus the light.
In the final classification, with one Audi followed by three Peugeots, the four first positions were occupied by cars using LED headlights.
Finally, note that this technology, which is already present on the rear lights of some road cars, will be rapidly used for road headlamps - and this has already been authorised by the EU.
Apologies for the slightly clunky English - that’s why I am not a professional translator. In any event, I found it interesting, as is RaceTech Harnessing’s website: http://www.racetechharnessing.co.uk/. I get the impression that in a few years' time we will look back on 'bulb' technology as something very quaint. Remember when number plates used to be black and white?