LEDs in Exterior Vehicle Lighting

Jeff Erion, Motor Vehicle Lighting Council

LED lighting is a complete paradigm shift in vehicle lighting. Filament bulbs have been the only means for providing illumination in and on vehicles since 1910, when the first electric lamps were fitted to a production model. Now, solid-state technology provides many benefits to the auto companies for styling and packaging, as well as promising a significant environmental impact: fuel savings.

LEDs require less than one-third the energy to provide an equivalent level of light compared with incandescent light sources, so the energy savings is evident from the start. Most luxury vehicles today are using LEDs for some of their rear lighting functions, but the steady reduction in the cost of LEDs and the availability of even higher output versions could provide major energy savings for a vehicle if used in all exterior lighting applications. That means better fuel economy and a corollary reduction in air pollutants.

In 2003, the US Department of Energy (DoE) assessed the effect of broad-based use of LEDs in niche lighting applications. Estimates for energy reduction and associated fuel savings were staggering (Figure 1). The potential savings in passenger vehicles alone would account for 1.4 billion gallons of fuel per year if every vehicle in the US today used all-LED lights. Truck savings potential is more than double that amount. Add to that the reliability and associated truck uptime improvement, and the value proposition for LED lamps is considerable.

Figure 1. Power requirements for today’s vehicle lights are compared with the power equivalent for LEDs. Usage data courtesy of Visteon Corp.

Headlights added

Headlights recently were added to the list of exterior lighting applications primarily because of the development of extremely high brightness white LEDs. All of the major car manufacturers are showing LED headlights on their concept vehicles. Likewise, the major lighting equipment manufacturers are demonstrating LED headlights at equipment shows. Toyota has indicated that it is planning to introduce an LED headlight on the Lexus 600H as early as 2007. Equally exciting news comes from Audi, which plans to introduce LED headlights on its R8 model in the 2007-2008 timeframe.

Electronic control of headlights will allow various forward-lighting functions, such as high and low beam, daytime running lights and adaptive front lighting (steerable headlights) to share LEDs. It is easier to turn LEDs on and off electronically than it is filament bulbs, so only the sources required to provide a function must be illuminated or modulated. The possibility of reducing the number of bulbs used will help further reduce the amount of energy consumed.

Efficiency improving

The technologies that create automotive-capable LEDs have not evolved completely. It is expected that lumens per watt will steadily improve and that the cost per lumen will continue to decrease. The best efficiency that can be expected from an incandescent bulb is about 15 lm/W. Halogen bulbs, used solely for headlight applications, can achieve no better than 21 lm/W. Conversely, LEDs of the future will be able to attain in excess of 100 lm/W (Figure 2). These factors will drive the implementation of LEDs from their use only on upscale vehicles to use on almost all vehicles. In as little as 10 years, the incandescent bulb could be nearing extinction on cars and trucks.

Figure 2. Lumens per watt have improved from one generation of lighting technology to the next, from incandescents to fluorescents to electrical discharge lights to LEDs.

LED market trends

Implementation of LEDs on US vehicles has grown to about 20 percent of the total rear light market. The main lighting functions that use LEDs are the stop- and center high-mounted lights, primarily because of the fast “on” time of the LED, which achieves full brightness in about 3 ms, whereas an incandescent light source requires nearly 200 ms (Figure 3). This difference can result in an additional 15 ft of stopping distance at 60 mph.

Figure 3. The LED (red line) achieves full brightness much more quickly than incandescent bulbs (blue line). It can add to automotive safety when used in rear stoplights, as shown here. Courtesy of Philips Lumileds 2006.

Considering the total number of lights on the vehicle shown in Figure 1, the industry has a long way to go to achieve 100 percent LED utilization. Europe and Japan have achieved much higher implementation rates of 40 and 50 percent, respectively. European and Japanese manufacturers tend to be early technology implementers, so their vehicles typically will have more LED applications when compared with US vehicles.

Fuel impact

LED efficiency is expected to improve and to expand usage into more and more functions. Although the current fuel savings contribution by LEDs is relatively inconsequential at 5.9 percent, the long-term view looks very good, with an ultimate improvement of greater than 80 percent over incandescent lighting predicted. The 20XX picture exceeds the projection made by the DoE by about 60 percent because that study did not include the improvements in LED efficiency expected in the future (Figure 4). The department projected 1.4 billion gallons based on more than 221 million vehicles versus 2.6 billion gallons in this study.

Figure 4. The potential power impact of LED implementation is shown on vehicles in the US at five and 10 years from today, along with the longer-term potential of LEDs when all vehicles might be equipped with them. These results are based on annual watt hours/vehicle × alternator efficiency (50 percent) × engine efficiency (25 percent)/33.4 kWh/gal.

Although 100 percent use of LEDs is not expected by 2016, the direction that solid-state lighting is going in is clear. The rapid growth of LEDs into the middle vehicle segments will dramatically improve product volumes, where the real effects of expected power savings can be seen. As long as LEDs are used only on luxury vehicles, only a few percent of the market will be affected. The middle range vehicle segment will increase volumes to more than 50 percent. If hybrids, electric and alternative fuel vehicle segments grow as expected in the next 10 years, that also will benefit the growth of LED applications. These vehicles will have to reduce parasitic losses (power) to achieve the highest fuel economy or miles per charge/fuel loading. Parasitic losses come from any part of the vehicle that results in added power consumption, including friction in the drivetrain, power drain from air conditioning, heated seats, radio and even the aerodynamics of the vehicle.

The speed of introduction is currently in the hands of the vehicle manufacturers; however, environmental and fuel costs may play a larger role in the adoption rate than they do today. Complete adoption of LEDs for exterior lighting on vehicles will provide significant fuel savings in the long term and, when combined with the broader use of LEDs in commercial/industrial applications, will result in significant energy reductions in the US.

Meet the author

Jeff Erion is an automotive lighting consultant with JA Erion LLC of Plymouth, Mich., and spokesman for the Motor Vehicle Lighting Council of Research Triangle Park, N.C.; e-mail: jaerion@charter.net.