After a decade of trickling mostly into specialized applications on high-priced vehicles, light-emitting diodes (LEDs) are poised to take a much larger share of the automotive lighting market over the next few years. Proponents of the technology say that there is no light source on an automobile, including headlamps, that cannot eventually be replaced by LEDs, and recent performance improvements are hastening what they consider an eventuality. Dieter Schaper, global director of Visteon's exterior product line team, points out that because of the recent doubling of LED light output, it is now possible to replace a halogen headlamp with "a handful of LEDs," something not possible just two years ago.
Why LEDs? There are a lot of compelling reasons why OEMs are switching from bulbs to LEDs, but the chief drivers vary based on where the light is located. On the interior, reduced power consumption and warranty costs get the most attention. In many applications, LEDs use less than a quarter of the power needed by an incandescent bulb, and with electronic hardware quickly proliferating throughout interiors, every watt saved in lighting is one that can readily be used elsewhere. With operating lives of up to 10,000 hours (compared to as little as 300 hours for a bulb), LEDs essentially never burn out, which means automakers don't have to shell out $30 or so in warranty payments every time a dealership has to replace a fifty-cent bulb. "All interior lighting will end up with LED," says Mike Godwin, general marketing manager for LED products, Osram Opto Semiconductors.
For exterior applications, achieving a unique styling statement is what automakers are seeking above all else, and the clean, high-tech look of LEDs is a key differentiator that grabs attention. And the fact that LEDs can be colorless until lit complements the current trend toward clear lenses on rear combination lights. Beyond this cool factor, LED light assemblies offer the practical advantage of being much thinner than conventional units (Visteon estimates up to 55% thinner), giving designers more packaging freedom. In front lighting, an application coveted by LED suppliers, developers tout the ability of headlamp arrays to control beam patterns by automatically switching independent LED chips on and off. This leads to some unusual and desirable capabilities like side lighting that illuminates curves when turning and automatic beam leveling that prevents blinding oncoming drivers.
Cost Woes. But all of this capability comes at a cost that most OEMs have generally been unwilling to pay. In answer to the question "Can LED take over all lighting in the car?" Schaper replies, "I don't see any limitations other than the price. The hurdle is the cost; it is expensive right now. Though every automaker is fighting for market share, they are not necessarily going for high tech solutions." After all, many incandescent bulbs have remained essentially unchanged for 20 years, making them a cheap, easy standard to plug into new designs. But on a growing number of applications, OEMs are willing to pay a premium for performance and long-term cost savings. Godwin says, "In certain applications the cost curves for LEDs and bulbs have already met." He cites instrument panel and radio unit lighting as areas where reduced heat and improved warranty numbers have outweighed higher unit costs, and points out that automakers are quickly migrating to LED use in center high-mount stop lamps because of much faster system performance. (One study indicates that the 1.8 millisecond rise time of an LED translates to an extra 24 ft. of stopping distance for a car moving at 65 mph when compared to the 250 milliseconds needed by an incandescent bulb.)
Still, when looked at as a percentage of total automotive lighting, LED use is just a sliver, and an expensive one at that. So why are LED makers so bullish? They have Moore's Law on their side. Because LEDs are semiconductor chips (albeit ones usually made of indium gallium nitride instead of silicon) they benefit from Intel co-founder Gordon Moore's famous pronouncement that the number of transistors per square inch doubles every 18 months. For LEDs this means lumens generated per watt of power consumed will continue to rise at a pace that far outstrips bulb technology, while manufacturing costs should fall precipitously as volumes ramp up. "Like all chips, LEDs really rely on high-volume. The moment you get into high volumes then it really comes down in price," explains Schaper.
Too Hot. LEDs have a problem with heat. Though they are known for cool operation, as the number of lumens per chip has increased, so has the excess heat generated, and dissipating that heat has become the chief technical hurdle for further LED development. Suppliers are experimenting with cooling fins, fans and even liquid cooling, but all of these potential solutions increase complexity, part counts and cost. "We don't want to make it more complex just to get a few more lumens," says Schaper. "The way forward is to keep cost under control and keep our packaging space advantage, not lose it to a large cooling system." But there's the rub. LED developers have to increase lumen output in order to have a shot at capturing any significant portion of the forward lighting market currently dominated by cheaper halogen bulbs, but cost-effective cooling currently remains out of reach.
LED Roadmap. Still, even with thermal management challenges, the move to LEDs in automotive lighting seems inexorable. Visteon will produce a low-beam LED headlamp for an unnamed OEM beginning in 2008, and Schaper estimates that by 2010 an all-LED car (including high-beam front lighting, the final sticking point) could be on the road. The most likely future growth path is for LEDs to gradually take over interior and rear exterior lighting while providing signal and day runner lights in hybrid assemblies that continue to use halogen or xenon for the headlamps. Eventually, LEDs would move into volume headlamp production as well. LED suppliers (many of which also make bulbs) are quick to point out that it will take many years for LEDs to become the dominant light source in vehicles, but it's clear that the days of the conventional bulb are numbered.