Car headlights are a gas, gas, gas

By T. Uncle

STATISTICS tell us that a large percentage of road accidents happen at night.

The figures also reveal that more than half single-vehicle fatalities occur after dark, even though most drivers spend 75 percent or more of their time behind the wheel during daylight hours.

It is an accepted fact that accident risks more than double at night.

The message is clear: improve after-dark driving conditions and the chances of survival on the roads will also improve.

At the 15th International Technical Conference on the Enhanced Safety of Vehicles held in 1996, in Melbourne, Australia, car lighting expert Dr. Burkard Woerdenweber from Hella KG in Germany said that a major reduction in nighttime fatalities could be expected in the next few years as new lighting technology is adopted by the car industry.

He cited developments such as "intelligent" front lighting, which adapts according to prevailing conditions, "ambient" interior lighting, which differs from conventional "point" illumination by identifying control location via "contour" lighting, and gas discharge headlamps as being the most significant of the technological changes that will become commonplace within the next few years.

Already, gas discharge, or Xenon, after the gas used in the bulb, headlamps are being adopted by various prestige car manufacturers.

Touted as being far more effective, yet less power-hungry than the quartz halogen headlights widely used by today's carmakers, gas-discharge headlights are the flavor of the moment with carmakers trying to convince would-be buyers of the superior technology built into their products.

Carmakers such as BMW, Mercedes-Benz and, most recently, Lexus with its GS300 model, have adopted gas-discharge headlights in order to gain a safety edge at night, as well as a marketing advantage.

Exactly what is a gas-discharge light? And how does it differ from the familiar quartz-halogen system that was only widely adopted a decade or so ago and itself was a major advance over previous lighting systems?

Basically, the big difference between a quartz halogen light and a gas-discharge light is that, instead of using a white-hot tungsten filament to provide the light source, the gas-discharge light uses an electric arc between two electrodes operating in a metal vapor mixture. In a way, not dissimilar to the principles operating a conventional fluorescent tube.

By doing this, the bulb does away with the failure-prone filament -- it is also more compact -- taking up little more space than a matchstick.

As well as this, it uses considerably less energy: Hella claims a gas-discharge light only requires 35 watts to produce twice as much light as a 55 watt halogen globe.

On top of this is an increased operational life due to the lack of a fragile filament.

It is claimed a gas-discharge globe has a life expectancy of about 2,000 hours, which essentially means it should last the life of the vehicle.

Hella says the more powerful "source luminance" of the electric arc allows the light pattern to be controlled more effectively, giving a more uniform spread and more precise aiming.

The company says up-close light can be reduced to minimize reflective glare on wet roads and that the "cut-off" point can be tailored to minimize glare for oncoming traffic.

The color of the light produced is also close to daylight, with a more bluish hue than the reddish-white luminance produced by quartz-halogen systems.

There is a downside, of course.

For example the manufacturing costs are high, because even though they consume less energy when operating, gas-discharge lights require considerable energy to start the discharge process.

The power required to light the discharge -- 12,000 volts -- is similar to the voltages used in a car's ignition system, while during the warmup stage, the bulb needs about 100 watts before settling down to a steady 35 watts.

To perform all these functions, the German lighting manufacturer had to develop a special electronic control unit that was small and relatively inexpensive, as well as being safe to handle.

However with the economies of scale that come with high-volume manufacture, it can be expected that the cost of installing gas discharge lighting will become gradually lower.

The world's drivers will welcome that.