Innovation: Bright idea for a car tail light you don't have to see till you have to: Optical techniques provide discreet rear signals that show only when they shine

A SAFER DESIGN for the rear light clusters on cars will make brake lights more visible, even in fog, and will overcome problems of following drivers seeing them flash when in bright sunlight. But car manufacturers may be taking more of an interest in the aesthetic applications of the new technology than in its safety factors.

John Hother of Sira, the contract research company where the light was developed, explained that the revolutionary light design makes it possible to cover the conventional red, white and orange filters with an outer mask that can be coloured to match the car's body paint. In effect, it takes the tail-light out of the way for car body designers

Sira has combined a number of simple optical techniques to make the rear light brighter and to overcome the 'sun phantom' and ''washout' experienced when bright sunlight hits existing rear light clusters. Inside the body-colour mask, the traditional single-layer red, white and orange plastic light covering has been replaced by a moulded version that is no longer smooth on its inner surface, but fashioned into a series of small lenses. These lenses channel the light from the bulb and, by way of the reflector, through some 2,000 tiny holes in the outer mask.

Concentrating the light through the lenses creates an intense central beam that can be seen from long distances. 'While the brightest part of a conventional rear light cluster today may be marginally of greater luminance, the Sira design provides a comparable light intensity over its full surface. And this makes it appear significantly brighter,' Mr Hother explained.

The tiny holes also solve the sun phantom problem, which occurs when sunlight is reflected off the internal reflectors of rear lights, making it seem to the car behind that the brake lights are on. In the Sira design, the holes in the outer skin amount to less than 15 per cent of the surface area; this means that only a fraction of the sunlight that is falling on the surface can enter the light housing itself, and there is no direct path by which it can be reflected back out. The external surface of the light also has a matt finish that virtually eliminates 'washout', which occurs when sunlight is reflected off the rear of a car, making it difficult to see from behind whether brake lights or turn indicators are on.

Sira is talking to two UK car manufacturers and one on the Continent about turning its demonstration prototype into a production model. Mr Hother said the design, which has exactly the same components as conventional rear light clusters, could be produced in volume at comparable cost.

He added, however, that because the manufacturers appear to be more interested in the design for its styling merits than its safety aspects, it will be at least five years before the new rear lights hit the road.

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