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Adaptive headlights give a better view of the road around curves and bends during nighttime driving. See car safety pictures.

Photographer: Tt | Agency: Dreamstime.com

How Adaptive Headlights Work

You're driving home from a weekend vacation. It's late at night, and the winding two-lane road has no streetlights. You approach a curve at 40 mph -- slow enough to make the turn, but too fast to stop suddenly if you need to. What's waiting there, just beyond the range of your headlights? A stalled car? A deer?

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With adaptive headlights, there's no guessing game. The lights turn their beams around each bend in the road, giving you a better view of what's ahead. Improved night driving isn't a trivial matter -- over 46 percent of fatal accidents in 2006 occurred at night, a number much higher than the proportion of driving done at night [source: FARS Encyclopedia, Public Roads].

In this article, we'll look at how adaptive headlights differ from standard headlights and find out how they can make nighttime driving safer. We'll also look at some headlight innovations in the works.

Standard headlights shine straight ahead, no matter what direction the car is moving. When going around curves, they illuminate the side of the road more than the road itself. Adaptive headlights react to the steering, speed and elevation of the car and automatically adjust to illuminate the road ahead. When the car turns right, the headlights angle to the right. Turn the car left, the headlights angle to the left. This is important not only for the driver of the car with adaptive headlights, but for other drivers on the road as well. The glare of oncoming headlights can cause serious visibility problems. Since adaptive headlights are directed at the road, the incidence of glare is reduced.

A car with adaptive headlights uses electronic sensors to detect the speed of the car, how far the driver has turned the steering wheel, and the yaw of the car. Yaw is the rotation of the car around the vertical axis -- when a car is spinning, for example, its yaw is changing. The sensors direct small electric motors built into the headlight casing to turn the headlights. A typical adaptive headlight can turn the lights up to 15 degrees from center, giving them a 30-degree range of movement [source: Audi].

If 15 degrees of sideward movement isn't enough, such as during low-speed turning in a parking lot or for especially sharp curves, additional lighting can supplement the headlights. Some BMW models are equipped with cornering lights. If the car has fog lights, small reflectors swivel to direct the fog lights off to the side. In the absence of fog lights, an additional side-directed lamp is installed with the headlights. When the car is moving slower than 25 mph (40 km/hour) and turning, the cornering lights can illuminate up to 80 degrees of additional area to the side of the car. When the car speeds up or finishes turning, the lights automatically turn themselves off [source: BMW].­

­The sensors in an adaptive headlights system prevent the lights from turning when they don't need to. If the car isn't moving or is moving in reverse, the adaptive headlights won't activate. This helps keep the lights from inadvertently blinding other drivers.

Read on to­ find out what other advantages adaptive headlights can provide -- and what cutting-edge technology the headlights of the future will be using.­

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Adaptive headlights are standard on BMW

Photo courtesy Ed Grabianowski

Self-leveling Systems and Future Headlight Technology

Most adaptive headlights systems also include a self-leveling system. Self-leveling headlights have an additional level sensor that determines if the car is tilted forward or back. For example, if a car is driving over a large bump, when the front of the car hits the bump, it lifts up. Standard headlights would briefly point up into the sky until the rear of the car moved over the bump and the car returned to a level position. You may have noticed this if a car driving behind you at night passed over a bump, such as a railroad crossing. The other car's headlights would flash briefly, as if the driver had blinked his or her high beams at you. This is actually the car's headlights temporarily pointing up and into your eyes instead of down at the road. With a self-leveling system, electric servomotors react to the level sensor and keep the headlights aimed down at the road, no matter the position of the car.

Self-leveling headlights are already required on new cars in Europe, and they're required on all U.S. cars equipped with bi-xenon headlights. Bi-xenon lights are so bright that they would blind other drivers if they didn't level themselves.

Adaptive headlights aren't yet standard equipment on most cars. In fact, only a few companies even offer them as options. BMW offers optional adaptive headlights on all models, while 335, 535, 7-series and M-series include them as standard equipment. Renault offers them as an option on some models, and the 2006 Volkswagen Passat includes them in the optional Luxury Package. Lexus, Audi and many high-end manufacturers also offer adaptive headlight packages.

Headlights of the Future

Auto designers are developing several innovations in headlight technology that should appear on production models in the next few years. Adaptive brake lights will allow you to see more than just the car in front of you applying the brakes. You'll also know how hard the driver is applying the brakes, giving you a good indication of trouble ahead or how much you yourself need to slow down. These brake systems will light up like normal brake lights under normal braking conditions. However, when someone presses on the brakes hard to make a more sudden stop, the brake lights shine more brightly. The lighting is progressive -- when someone really stomps on the brakes, the very brightest brake light comes on, while lesser degrees of braking force result in brightness in between "normal" and "full stop."

Single-source fiber-optic lights could revolutionize auto lighting by allowing for a wider variety of lighting options and optimal lighting configurations. A single-source system uses one light located somewhere in the inner workings of the car. Fiber-optic strands then carry the light to wherever it's needed. Instead of two headlights, a car could have a wide light-emitting pattern on the front. The fiber optics could be manipulated by small motors to allow even more versatile adaptive lighting. The drawback for the time being is that the fiber optics lose a lot of the light's intensity as they carry it, so a very bright single-source is needed [source: Smart Motorist].

For more information on adaptive headlights and other topics you might be interested in, check out the links on the next page.

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Lots More Information

Related HowStuffWorks ArticlesMore Great LinksSources
  • Audi. "The 2008 Audi A8: Features and Specifications." http://www.audiusa.com/audi/us/en2/new_cars/Audi_A8/A8/Model_Features.html
  • BMW. "Redefining the Speed of Light." http://www.bmw.com/com/en/newvehicles/mseries/m5/2007/allfacts/ ­ergonomics_ahc.html
  • National Highway Traffic Safety Administration. "Fatality Analysis Reporting System." http://www-fars.nhtsa.dot.gov/Crashes/CrashesTime.aspx
  • ­Opiela, Kenneth S. "Driving after dark: researchers at FHWA are striving to improve nighttime visibility, making roads safer for motorists and pedestrians." Public Roads, Jan-Feb, 2003­. http://findar­ticles.com/p/articles/mi_m3724/is_4_66/ai_97723968 ­
  • ­­Smart Motorist. "History of Modern Lighting." http://www.smartmotorist.com/lig/lig.htm