From Chicago Tribune

http://www.chicagotribune.com/classified/a...,1990272.column

Bob Weber
Car light, car bright
Automakers look ahead as lamps evolve

Published January 13, 2003


Though they taught us about the Dark Ages, that period in Europe when education and the population declined between 400 and 900 A.D., most schoolteachers fail to cover the Dark Ages of automobiles, when cars didn't have lights.

The earliest motor vehicles didn't need lights because they were driven only during the day.

When lights first appeared on cars, they were candles, useful only to alert others a car was approaching. Oil lamps and lanterns did little to illuminate the road and, like candles, could be easily blown out.

Lanterns gave way to acetylene gas headlamps with parabolic reflectors, the kind of reflectors in flashlights.

Carbide (calcium carbide) chunks in the lower chamber of an hourglass-shaped affair generated acetylene gas as water dripped from the chamber above. Once ignited by a flint-and-wheel device much like a cigarette lighter, the acetylene burned with a bright white flame from a jet in the center of the reflector.

The enlightenment, as it were, occurred when electric lights appeared on cars around the turn of the century. Early electric lights were bright, but unlike today's headlamps, did little to focus the light. Glare from oncoming traffic was a problem.

To overcome the early glare problems, some cars added cable controls so the light assembly could be "dipped" when there was oncoming traffic. In many parts of Europe, what we call the high-beam is the standard beam, which is "dipped" to the low beam for oncoming traffic. By 1915, red rear lamps and yellow brake lights had been introduced.

Introduced in 1938, the incandescent sealed-beam lamp, similar to ones we use today, was a major advancement in longer-life lighting because this new "sealed" lamp better protected the filament, the wire that gets hot and glows to provide the light, and prevented weather damage. Also, the reflector was better protected. But it was still an incandescent light source. Over time, the light output declined and the filament burned out.

In 1962 the first halogen headlamp was introduced in Europe and by 1971 the first double filament--for high and low beam--halogen bulb was approved worldwide. A halogen bulb is an incandesent bulb with a halogen gas that allows filament to burn brighter.

The most common halogen bulb, dubbed the H4, could be replaced without replacing the headlight lens and reflector. There were some problems, however, installing the bulb in glass assemblies while early plastics tended to yellow and scratched easily.

In the late '70s the halogen sealed beam became popular on dometic cars and significantly changed automotive lighting.

Halogens quickly became popular with motorists who preferred a whiter light that illuminated objects closer to their natural color. Halogen lights also provide more consistent performance as they age.

The new star in the automotive universe is high-intensity discharge lighting. Introduced in the European market in 1991, HID lights made their debut in the North American market on the 1996 Lincoln Mark VIII.

HID bulbs have no filaments, generating light from a discharge between two electrodes in a small "arc tube" filled with xenon and mercury. The electrical discharge excites the mixture, creating a brilliant white light that is even closer to natural sunlight than are halogens. Many people say the light almost looks blue. HIDs do create more light in the shorter wavelengths of the blue end of the spectrum than other lamps.

HID lights are a bit like the arc lights used for movie premiers and shopping-center grand openings. HID systems generate three times the light output of a halogen bulb. It is more constant over time and can last up to 10 times longer than today's standard halogen lamps.

Because they provide improved down-road illumination, HIDs are quickly becoming the light source of choice. As the technology matures and costs are reduced through wider adoption of the product, HID will make its way into mainstream vehicles.

Though these lights require higher voltages--about 30,000 volts to strike an arc and 80 to sustain it--they consume less overall energy because the current (amperage) draw is lower. To put it in perspective, typical halogen lights draw about 55 watts while HIDs draw slightly more than 40 watts, savings in power of more than 25 percent.

The drawback to such bright, full-spectrum light is glare, especially when there are reflections such as from wet roads.

Lighting engineers and the government are working on the problem. Don't be surprised to see regulations calling for self-leveling lights, similar to those in Europe, on American autos. At least the headlights will remain properly aimed, even if the load in the car changes.

Experts from OSRAM Sylvania told us that we may see LED (light-emitting diode) headlights in two or three years. Selected GM models already have a night vision system, but the next big thing may be even infrared-sensitive windshields to help drivers see down the road.