Long before Edison put a filament into a glass bulb, electric light meant current jumping across an arc. The light was brilliant, but striking and maintaining a stable arc wasn’t easy or cheap. Today, High Intensity Discharge or HID headlamps are established in high-end models, and is moving toward the mid range.
What makes a “good” automotive lighting system? For years, sheer power was the yardstick for measuring lighting performance, power that was often measured in terms of energy consumption. While wattage is still a commonly quoted specification, Halogen and HID technologies let engineers tailor light quality in other important ways, says Ted Hardenburgh, product manager for Osram Sylvania Inc.: “Filament based is very limited as to out put, and as importantly, the colour. Colour temperature is the way lighting engineers measure the wavelength of light emitted, most commonly seen as the “whiteness” of the light.” Colour temperature is quoted on most product spec sheets in a special scale called Kelvin. A just like “normal” temperature scales, higher is hotter, and in terms of light output, whiter. Whiter light is optimal for clear night driving, and while halogen is a step up from conventional incandescent, HID is superior, according to Hardenburgh: “With HID you can do the chemistry to obtain a good crisp white light.”
Generating that white light is more complex, however, than heating a tungsten wire, says Hardenburgh: “It takes electronics to operate it. The systems take 12v input and convert it to an AC output; the circuit uses a higher starting voltage generated by an “igniter.” If you look at HID street lighting, it works its way on slowly. On automotive lighting, it has to be instantaneous. The igniter delivers a 25,000 volt hot start, but the ballast needs only 80 volts for continuous operation.”
From a service perspective, if you’re working on a vehicle harness with the lights on, there are potentially dangerous high-voltages present. Repair should always use the correct shielded cable, and wherever possible, disconnect power to HID units before service. Unlike some capacitor-laden devices such as video monitors, though, units are safe immediately after power is switched off.
incandescent tail, stop and turn lighting
Just as HID is changing the way vehicles illuminate the road ahead, another acronym, LED (light emitting diode) is poised to replace filament-based lighting at the stop, turn and tail positions. Already seen as the high mount third brake light on several auto models, and used extensively in commercial trucking applications, LED lighting has several advantages over incandescent lamps. The most important is safety. LED’s turn on at essentially the speed of light, compared to incandescents that must warm up to operating temperature before glowing.
The difference in stopping distances for following drivers reacting to LED brake lights is considerable, declares Matt Forner, director of product development, aftermarket, for Grote Industries: “Anywhere from 25 to 60 feet depending on road conditions.” Heat or the lack of it is another attractive feature, allowing designers more flexibility in designing reflector/lens assemblies, as well as sockets and associated wiring. Durability is another advantage, says Forner: “Filaments are affected by vibration and shock, which is a typical failure mode for incandescents. LED units are assembled in an epoxy compound, and there’s no filament to break. LED’s can burn for eleven years straight. We currently use multiple diodes to get the same light output, although with improving technology, we’re able to use one or two diodes for marker lamps, and ten for a stop/tail/turn lamp.”
The long life expectancy and flat packaging of LED packages also allow service procedures that remove the whole unit from the outside, eliminating the need for access to the back of the reflector assembly for greater rear body design flexibility. And with low power consumption, a service life measured in years combined with a failure mode that allows slow deterioration of the lamp as each LED fails, consumer acceptance of the technology should be seamless. Replacement costs, however, will be expensive compared to incandescent bulbs. The final factor from the service perspective is one that current regulations don’t take into account: What constitutes failure? With a typical unit comprising multiple LED’s, individual failures won’t leave the unit dark, but at some point it should be replaced. How many LED’s “out” are tolerable will depend on how and when Provincial regulators examine the issue.
Will HID and LED take over?
Technology is fine for luxury cars and light trucks, but will HID and LED make it to the mainstream? The answer is yes, but the real question is, when? Large players like Osram Sylvania have a strong presence in HID, and industry giant General Electric is poised to become a leading OEM supplier, suggesting that the industry expects real growth in consumer acceptance. Patrick McElhaney, general product manager, automotive segment, for General Electric relates: “It depends on the time horizon. HID lighting provides benefits to the market that are real, and over time it will become a significant proportion of the market. It’s a more expensive option; it will be many years, beyond five years, before it becomes the sole source of automotive lighting. You’re already seeing it on high-end automobiles, and that growth will accelerate, but it will take time.”
Unlike Osram Sylvania, General Electric will not offer aftermarket products immediately, and will launch products into the OE market this fall. According to McElhaney, “Car platforms are designed many years in the future, so new technology today will appear on vehicles in 2003 or 2004. The total purchase price is higher and it will take time to work through the market. In time, economies (of scale) will help, but it is a more expensive design solution.” LED technology is also a good bet for widespread application. Grote’s Matt Forner states: “They’re starting to look at it on passenger cars; it will take a couple of years. In the heavy-duty market, your return on investment is 300 percent. It’s our fastest growing market segment right now.” Will HID replace halogen in mid range applications as well as the high end? Like many other industry executives, Patrick McElhaney is enthusiastic: “Absolutely. But it will take time.”