Chicago — The venerable filament-type tail- and headlight bulb — which succeeded candles and oil lamps as the state of the art for automotive exterior lights early last century — may finally be garaged in the next decade, as a new breed of brighter LEDs is designed in to vehicles.

Two LED suppliers said last week that they are working on 100-lumen designs that would replace incandescent bulbs in light assemblies on a one-for-one basis (as opposed to the diode clusters now required to replace a single incandescent bulb). And a tier-one supplier said it is talking to several automakers about employing LED-based headlights as soon as the 2008 model year.

The bright new LED technology is seen as an alternative not only to incandescent bulbs but also to the current crop of tiny LEDs, which must be employed in groups of as many as 60 to provide sufficient brightness for rear exterior lights. By offering a higher output, the new LEDs could migrate from center high-mount stop lamps to lights, brake lights and turn signals on the rear of vehicles. LEDs could also, for the first time ever, begin to serve in headlight assemblies.

"This is a monumental change for the auto industry," said Jeff Erion, R&D manager for exterior systems at Visteon Corp. (Dearborn, Mich.), which recently demonstrated a working LED-based headlight assembly.

"Since 1914," he said, "there has been only one way to create light on a car. Now we're looking at a technology that can replace every filament bulb on the exterior of every vehicle."

Proponents of the technology say that LEDs are superior to incandescent bulbs because they respond far faster (thereby giving neighboring drivers more time and distance to react to the flash of a brake light or directional signal), last the life of a vehicle, are more energy-efficient and better resist vibration.

Suppliers of automotive lighting assemblies, however, say LEDs must clear some hurdles before achieving widespread use. "In terms of cost, LEDs and bulbs are not at all comparable," said Jianz-hong Jiao, general manager for engineering technology at North American Lighting Inc. (Framington Hills, Mich.), a subsidiary of Keito Manufacturing Co. Ltd. of Japan. "It's a matter of a few cents vs. a few dollars.

"There are also some issues of durability — not in the LEDs themselves, but in the associated electronic devices, such as circuit boards. Those still need to be looked at."

Still, LEDs have been making steady inroads on the rear exterior of vehicles over the past few years, particularly for use in center high-mount stop lamps.

Suppliers estimate that between 80 and 90 percent of the high-mount lamps in current Asian models use LEDs. Seventy to 80 percent of the high-mounts on European models and more than 50 percent of those on U.S.-made vehicles are said to employ LEDs as a light source.

Further, the new breed of brighter products is expected to take LEDs into rear-vehicle applications, where they have been used only sparingly up to now.

In stop lamps, for example, LED use over the next few years is expected to grow far beyond its current market penetration of about 2 to 3 percent. The same is expected for turn signals.

"All luxury vehicles in the next two to three years will have LED signal lamps," predicted Erion of Visteon.

The key to such success is the availability of brighter LEDs. At least two suppliers — Lumileds Lighting (San Jose, Calif.) and Osram Opto Semiconductors, Inc. (San Jose) — are working on 100-lumen designs that could be employed in production vehicles as soon as the 2007 model year. The brighter designs are said to be 10 to 20 times more powerful than existing products, which typically range from 1 to 5 lumens in the smallest devices. Lumileds executives said their company already markets 30-, 42- and 50-lumen products as the Luxeon line.

When the 100-lumen products reach the market, a single such device will reportedly be capable of replacing dozens of smaller LEDs. In approximately a decade, suppliers expect vehicles to employ 10 or more of the diodes (six in back, four in front) on the exterior, ultimately creating an annual market for at least 160 million exterior LEDs in the United States alone.

Lumileds engineers say they plan to accomplish all that by using two key types of semiconductor materials: indium gallium nitride and aluminum indium gallium phosphide. AlInGaP, they say, is the key material for creating red, orange and amber LEDs, which are mostly employed in the vehicle's rear exterior. InGaN emits blue light and, when combined with a phosphor conversion technology, can be made to produce white light.

"You have to have the best materials, you have to get the best phosphor and you need to apply the phosphor in a way that creates a very robust white emitter, if you want the best optical solution," said Leonard Livschitz, director of automotive business development for Lumileds.

Another key to creating brighter devices, engineers say, is larger semiconductor dice. "Efficiencies approaching 100 lumens are realistic as we get to larger and larger dice," noted Jonathan Wafer, product-market ing manager for visible LED lamps at Osram Opto Semiconductor. "To get that kind of output, you take the big chips and drive them hard, with currents approaching 1 amp. Then, the challenge becomes an issue of system thermal management."

Suppliers claim the higher-power devices are critical to the LED's success in exterior lighting applications because they let automakers cope more with packaging constraints.

"Hypothetically, you can always use LEDs to light up any function," Livschitz said. "But space is limited at the rear of the vehicle, so you're better off with one device that offers higher power."

For suppliers of automotive LEDs, the holy grail is the headlight. Most suppliers expect to see the first all-LED-illuminated vehicle reach the market within five years.