Headlight safety
An illuminating look at headlight safety

Headlights make night driving possible, especially on unlit roads. They aren't perfect, though: A study conducted by engineers at the Automotive Research Center and the AAA National Office found that many headlights may not provide adequate illumination when driving at higher speeds—or, in some cases, speeds as low as 40 mph.1

The reasons for this include variations in power between types of headlights, deterioration of older headlight housings, and the need to prevent glare from affecting oncoming traffic. Headlight shortcomings have serious safety implications: Only 25 percent of driving takes place in darkness, but 50 percent of crashes occur in that same period.

How light type affects safety

Halogen reflectors/projectors

Halogen lights are the most common, with more than 80 percent of all vehicles on the road today using them. Halogen bulbs work just like household incandescent bulbs: Electricity runs through a metal filament, which heats up and glows brightly. There are two methods used to focus that light and prevent glare. Reflectors, the older kind, use mirrors, while newer projectors add a lens and other mechanisms for a more focused beam. Halogen bulbs have short lifespans but are extremely cheap.

High-intensity discharge lamps

Often recognizable by their blue or white tint, high-intensity discharge bulbs provide more light with less electricity than halogens. Instead of a filament, HID lights use a sealed tube containing a gaseous mixture of xenon and metal salts. Running an electric arc through the tube heats the gas into light-emitting plasma, similar to a fluorescent bulb, but brighter. HID bulbs last longer than halogens but are more expensive.

Light-emitting diodes

LEDs have been around for decades in alarm clocks and other simple devices, but recent advances have brought them to the cutting edge of headlight tech. Distantly related to the silicon chips that run computers, LEDs create light by running electricity through a chemically treated semiconductor that releases photons. Their simplicity makes them extremely bright, efficient, and long-lived, with the trade-off that upfront costs can be much higher than for other bulbs.
  • Research revealed that even the most advanced lights operating at maximum brightness were still only safe up to 55 mph on unlit roads. That's because even with the best headlights, object visibility at night is reduced by as much as 60 percent compared to daytime driving. For less advanced headlights, such as common halogen reflectors, drivers can only go up to 48 mph on unlit roads before they're outrunning their high beams, and only 39 mph before outrunning low beams.

  • Halogen reflectors


    Low beam range: 300 feet
    Highest safe speed on unlit road: 39 mph

    High beam range: 400 feet
    Highest safe speed on unlit road: 48 mph

  • Halogen projectors


    Low beam range: 400 feet
    Highest safe speed on unlit road: 45 mph

    High beam range: 500 feet
    Highest safe speed on unlit road: 55 mph

  • High-intensity discharge lamps


    Low beam range: 400 feet
    Highest safe speed on unlit road: 45 mph

    High beam range: 500 feet
    Highest safe speed on unlit road: 55 mph

  • Light-emitting diodes


    Low beam range: 450 feet
    Highest safe speed on unlit road: 52 mph

    High beam range: 500 feet
    Highest safe speed on unlit road: 55 mph

Other safety considerations

Cleanliness

AAA’s study of headlight effectiveness used clean systems with clear lenses. Older lamps, however, may be less effective because of “hazy” plastic lenses or other deterioration.

 

  • AAA testing found that restoring headlights with commercially available products doubles their maximum light intensity, and reduces glare-producing light scatter up to 60 percent.
  • Despite the benefits of headlight restoration, another recent AAA survey discovered that only 20 percent of Americans have performed such service.

High beams

High beams increase the distance that drivers can see, but motorists often don't use them when they should. 

 

  • The study found that on average, high beams provided 28 percent more forward illumination than low beams.
  • Nearly two-thirds of U.S. adults who drive at night say they do not regularly use their high beams. This is despite the fact that America’s rural roads, which usually lack overhead lighting, account for 40 percent of vehicle miles traveled annually.

Glare

Glare from other vehicles’ headlights can reduce visibility. The issue can present itself in a number of ways.

 

  • Discomfort glare is uncomfortable or distracting, but doesn't substantially reduce the driver’s ability to drive safely. Common sources include cloudy headlight covers, the unusual tints and shapes of HID and LED lights, and poorly aligned headlights.
  • Disability glare creates a substantial reduction in a driver’s vision, and thus their ability to drive safely. Eye health issues such as cataracts are a common cause of disability glare for older drivers.
Ways to stay safe

 

If possible, use high beams. Sometimes it’s impractical, such as when there are many oncoming vehicles, but otherwise, using high beams is substantially safer than not.

 

Check that your car’s plastic headlight housings are clear. If they have begun to go hazy or cloudy, get a do-it-yourself restoration kit.

 

If purchasing a new car, look into what type of headlights it has. Some models may use halogen lamps on the “base package,” swapping them out for more effective HID or LED lamps on pricier trims.

 

Monitor your speed when traveling at night on unlit roads. It’s easy to lose track of how fast you’re going on a dark, wide-open highway, but it’s dangerous to outrun your lights. Don’t overestimate how far down the road you can really see; highway signs and markers are visible from much farther away than a non-reflective person, animal, or object is.

 

If you are 60 or older and have problems with headlight glare, have your vision examined. You may need treatment for cataracts or other eye issues.