The headlights of most vehicles do a poor job of lighting up especially dark roads, according to tests performed by the Automobile Club of Southern California's Automotive Research Center (ARC). "By failing to properly light roadways at moderate speeds, a pedestrian or animal may not become visible to a driver until it's too late to stop," explained Megan McKernan, manager of the research center.
ARC's study found that halogen headlights—which the auto club says are on 80% of the vehicles on the road today—"fail to light the full distance necessary for a driver to detect an object or obstacle in the roadway, react, and come to a complete stop" on unlit roadways at speeds as low as 40 mph. While such roads are typically rural, they account for 40% of all vehicle miles traveled annually.
Halogen headlights have a tungsten filament that glows when electricity passes through it. Enclosing the filament in an air-tight chamber filled with a halogen gas improves longevity and output.
High-intensity discharge (HID) headlights, sometimes called xenons generate light by producing an arc between two electrodes suspended in an inert gas. HIDs last longer and burn brighter than halogens, but the bulbs are more expensive.
LED headlights are comprised of light-emitting diodes, semiconductor chips that produce light via electroluminescence when electricity is passed through them. They have no filament, no moving parts, and can be combined into almost any arrangement. They are much more efficient and durable than halogens or HIDs.
High-beam settings on halogen headlights improved sight distances by 28% at the testing facility, but in real-world conditions only provide enough light to safely stop at speeds of up to 48 mph—well below what people travel on many rural roads. HID and LED headlights illuminated dark roadways 25% further than halogens, but still failed to do an adequate job at highway speeds.
"While it's encouraging to see the safety benefit that newer headlight technology offers to drivers, there's still room for improvement," said John Nielsen, AAA's managing director of automotive engineering and repair. He noted that better technology is available in European vehicles, but U.S. regulations limit the light output for vehicles sold in the United States.
Drivers can enhance their vision and visibility with these tips:
- Make sure headlights and windows are clean and in good condition. Dirty headlights and windows can scatter light. And plastic headlight covers may get cloudy with age, which can limit effectiveness. Keep these elements clean and clear, and replace cracked lenses and burned-out bulbs.
- Keep headlights properly adjusted. Headlights that are properly aimed will illuminate the road better and will be less likely to blind other road users. Have the headlights checked the next time the vehicle is serviced.
- Be considerate about using your high beams. Dim the headlights when approaching other users of the roadway so as not to blind them.
- Don't use fog lights if the weather is clear. Fog lamps—used in conjunction with low beams—can be a great help in foggy conditions. Avoid using fog lights under clear conditions, as this can create glare; and never use them alone.
