Issue: Mar 2003


LED-powered headlights are just over the horizon



by John Peter


Guide Corp. brought its prototype LED headlamp to SAE. The combination lamp offers flexibility to designers and a place for forward lighting LED technology in turn signals and fog lamp applications.
LEDs, those little light emitting diodes that light digital watches and alarm clocks, are taking over the automobile.

Advancements in technology have seen them move from stop lamps, to interior, to side marker lighting and onto the rear of the vehicle in tail light applications. They not only offer flexibility in design, but a vehicle with full LED lighting offers a potential 80-watt energy savings over one equipped with conventional bulbs. To engineers searching for power to run all of those new telematics features, thats a big energy savings.

LEDs are a perfect lighting source for rear combination tail lamps because the red and amber lights dont need to be filtered through colored plastic. A red LED offers a 10 to 15 percent energy saving over a red-filtered incandescent bulb. And LED manufacturers are developing ways to make them brighter. With LED tail lamps becoming more prevalent, how long before we see LED-powered forward lighting?

Most experts agree they are in the near future.
- I think that you could make a legal lamp now, says Michael Godwin, product marketing manager for Osram Opto Semiconductors. - The technology is there in terms of lumen output and brightness.

- Its not far away at all, adds Jim Loeffler, automotive sales manager for Lumileds, an LED manufacturer. By 2007 the technical and commercial feasibility will be there to get it done. Ron Steen, director of lighting R&D for Schefenecker sees production LED head lamps available by 2006 as standard equipment on premium segment vehicles.

I see this as the opportunity to do something really unique on the front end, Steen says. Jason Bonin, vice president for business development, lighting technology, Hella North America, agrees, saying the industry may see a couple of cars coming into the market with LED headlamps by 2005 or 2006. But he says that the technology could show up in forward signal and auxiliary lighting applications within the next 18 months. It's already been established and proven as concepts, Bonin says.

Guide Corp. and Lumileds showed a concept LED headlamp at SAE this year and DMB Refelx, a Quebec, Canada-based automotive lighting manufacturer has built prototypes for both Visteon and Valeo.

The Cadillac 16 concept, shown at this years Detroit auto show was equipped with LED head lamps that Steen says are very similar to the prototypes that his company is working on with General Motors.

Theoretically you could make an LED today thats as bright as a halogen bulb. But the conditions to do that would require the LED to be driven at a very high power level. The kind of heat generated at that power level would be fatal to an LED, so the heat needs to be dissipated. The answer is to create an LED package and implement that package into a lamp system thats very thermally efficient. The more heat you draw away, the higher you can drive the power.

There is also the issue of optical performance creating LED lighting that meets the SAE and ECE standards for beam patterns. You cant just flood light like a spotlight, Godwin says. You have to be able to cut the light off to meet the beam pattern.

The only way to get an LED headlamp on car is by having really high-efficient optics. Steen says that a traditional HID source is about 30 percent efficient, producing 3,000 lumens at the source but only putting about 800 on the road. A halogen bulb has about 1,000 lumens available, and can effectively 300 on the road.

We are trying to get about 70 percent efficient optics, Steen says. The only way that do that is by having extremely tight tolerance on the LED. The tolerance issue is going to be a significant one for the auto industry.

The LEDs biggest enemy is heat. Lumileds has developed SnapLED. The LEDs snap into a formable substrate that serves as both a power source and heat sink.

LED lighting is unique because the performance of the technology is being driven by LED suppliers, not by the auto industry. HID and halogen lighting are principle automotive applications, Bonin adds. LEDs are being born out of other applications, be it medical, commercial or residential. The environmental requirements of a typical automotive headlamp are so significantly different than any industrial, residential or general lighting application. And thats why its a strategic issue to establish a supply chain for automotive lighting.

But the rapid growth of commodity lighting will help lower the cost of the technology a fundamental issue that Bonin says is the only thing hindering the implementation of LEDs in forward signal and auxiliary lighting applications.

The Chinese semiconductor industry is in the process of installing 80 reactors in Taiwan to supply white LEDs to the general illumination industry. Steen says that as soon as they are on line and capacity goes up, the bright white LEDs are going to be cheap. And as more research dollars are pumped into the development of a brighter white LED for the general illumination industry, the auto industry will benefit. Godwin says that if the LED trend continues, the technology will see 30 times growth in brightness over the next 10 years and cost will reduce at the same factor. Once the cost is down and a business case can be made for the technology, then the benefits kick in.

The LEDs are easily integrated into other electronics systems. Their low power consumption makes them an ideal application for hybrid vehicles.

Osram designed a prototype LED fog lamp for Fords Tonka truck concept. The unit measures 20 by 10 centimeters. Hellas Jason Bonin says that applications like this could show up on production vehicles in the next 18 months.

While the first LED headlamps may look very similar to todays halogen or HID-powered stock, LEDs will most likely change the way we design cars in the future.

Since they are point source you can do a lot with the styling, says Phillip Reismiller, director of research and development for Guide Corp. With an HID you have one light source, but with LEDs you have multiple light sources, so you have a lot of possibilities. What you are talking about is package size, thin technology, says Michael Rohnert, director of sales and marketing for Osram Sylvania, the ability to wrap, being able to do some different dimensional stuff.

The projector units that are used in conventional headlamps are about 400 mm deep, which is taking up a lot of the engine compartment and eliminating some of the offsets that stylists can work with. We really have not tried to wring out thickness from it a whole lot yet, Steen adds, but we can get LED lamps down to 100 to 150 mm in depth.

By reducing the big optic and big pocket needed for a bulb you not only save space, but also reduce some of the manufacturing costs. A smaller lighting package would use less plastic and require fewer parts for assembly making it easier to build into front end modules.

Rohnert says that getting thinner is of real interest to automakers. Osram developed an LED fog lamp for the Ford Tonka truck concept that is less than an inch thick and Schefenecker is launching a production 10 mm thick peel-and-stick LED stop light.

My dream, says Schefeneckers Steen, to have the first peel-and-stick headlamp.

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Making LEDs

Its not rocket science, but its close.

LEDs (Light Emitting Diodes) are semiconductors made by a process called metal organic vaporphase epitaxy, the same type of process used to make computer chips. The LED chips are grown atomic layer by atomic layer in controlled laboratory conditions.

Inside the reactor, temperature, pressure and the mixture of the gasses are finitely monitored as the layers build into a chip that has the proper energy well to create light. LEDs come in several varieties. The two used most for automotive lighting applications are Indium Gallium Nitride (InGaN) that produces the green and blue colors and Indium Gallium Phosphide (InGalP) that produces red, yellow and orange.

Mixing all three chips together will give you white. Another way to make white is by adding a phosphor to a blue chip. The light emitted from these chips falls in the visible light spectrum. Blue is at the lower end of the spectrum and green and red fall at the higher end. Thats why the red chips look brighter than the blue ones. Because red LEDs are used extensively outside of the automotive industry in applications such as traffic lights and railway signals, the rapid advancements in the material system used to create red chips have helped to increase their units-per-wattan industry measurement for brightness.

Increases in brightness have also come through experimentation. There are two mechanisms built into each chip, a mechanism that creates light and a mechanism that extracts light. Growing thinner chips increases the efficiency, and experiments have shown that by flipping the chip upside down, the efficiency for extracting light is increased, which makes them even brighter.

LEDs can also be designed to create light in the invisible side of the spectrum. Infrared diodes work the opposite of an optical chip, absorbing infrared light and turning it into an electrical impulse. This type of chip is used in crash avoidance systems.
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Where Do We Go From Here?

Organic LEDs offer a world of opportunities.

While LED technology has already taken over the vehicle interior, a new technology promises to make them smaller and add some interesting functions. OLED, or organic LED is created through photolithography, where the LEDs are imbedded in a chemically-coated film, creating something similar to pixels. A computer can control how different regions, or single pixels are lit and what color they will be.

Osram is currently working on the Polymer OLED technology with Three-Five Systems, a manufacturer of flat panel screens and liquid crystal displays. The technology is well-suited for handheld devices like PDAs and cell phones, but theoretically you could apply a large sheet of the film on a window that would be transparent until an electrical charge was sent through it. In essence, you are picture window becomes your television screen Michael Godwin, product marketing manager for Osram Opto Semiconductors, sees this technology as perfectly applicable for automotive instrument panel and layered over the instrument cluster.

Real estate wise, you want to put more stuff on the IP. Theres benefit in a material thats transparent, until you need to see it, Godwin says. You can use the technology to create flexible instruments, or better yet, a navigation screen.


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