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http://www.consumerreports.org/cro/c...view/index.htm
Blinded by the light
Glare from those chic blue HID headlights has many drivers seeing red. Here’s why some lights can be a problem and what you can do.
Odds are, you love high-intensity discharge (HID) headlights if they’re on your vehicle. Lighting tests we’ve begun as part of our vehicle evaluations show that low-beam HID lights flood the roadway with a wider, brighter, more uniform light than regular halogens. But drivers on the receiving end of that light describe it in less-than-glowing terms.
When the National Highway Traffic Safety Administration (NHTSA) announced that it was looking into complaints about glare from HID lights, high-mounted sport-utility-vehicle lights, and fog lights, most of the roughly 4,000 responses that poured in complained about HIDs.
The numbers are especially significant considering that HID-equipped vehicles account for only about 1 percent of U.S. cars and trucks sold.
Automakers note that HID headlights meet current federal standards and attribute the complaints about them to a tendency for drivers to stare at the lights’ distinctive blue-white hue.
But our research and headlight tests of 41 vehicles--some with halogens, some with HIDs--show that HIDs do produce more glare, which is the temporary annoyance or blindness caused by bright light in your field of view. Dirty glasses or contact lenses can increase glare. Experts also say its effects become more noticeable after age 50. While HIDs’ blue hue is part of the glare problem, much of it lies in how their brighter light is distributed.
NHTSA is expected to begin proposing new standards for headlights later this year. Areas under study include the effect of blue light on the eye and the degree to which SUVs’ high-mounted lights cause glare. High-mounted HID lights can be especially glaring; we estimate that they zap vehicles ahead with up to 30 times more light than car-height halogens. Our HID-equipped 2003
BMW X5 and 2003
Range Rover SUVs prompted many oncoming drivers to "flash" us with high beams, even though we were using low beams that were properly aimed.
Glare isn’t the only headlight concern. Accident data and our test results suggest that even bright lights may not be bright enough where it counts. While we’re still gathering the data needed to include headlight Ratings in our vehicle scores, we found some strong performers so far. We also found the HID lights on the
Audi TT and halogen lights on the
Chrysler Sebring and
Pontiac Grand Prix unimpressive.
Varying headlight performance and glare are reasons to perform a nighttime test drive before buying a new vehicle. Here’s what HID headlights do well, and why some are so annoying. We also detail what you can do to protect yourself from glare, and how you can encourage NHTSA to set standards for safer lights.
HID headlights vs. halogen headlights STARK CONTRAST An HID beam’s sharp edge between light and dark causes the beam to “flash” other drivers when the car travels over uneven surfaces.
FADE-OUT Halogens tend to produce a more gradual shift from light to dark.
(Both photographs show headlights projected against a wall.)
More light, but mostly to the side
Unlike standard halogen bulbs, which produce light by heating a tungsten filament, HID bulbs send a high-voltage arc across two electrodes. This excites a gas, usually xenon, inside the bulb and vaporizes metallic salts, which sustain the arc.
The result is two to three times the light of halogens while using one-third less energy. Carmakers add that HID bulbs should last much longer than halogen bulbs. But at about $600 per vehicle, those benefits come at a cost.
What the law allows. Federal standards allow high beams to throw lots of light far ahead, but limit low-beam levels for oncoming drivers to minimize glare. Carmakers typically channel an HID’s extra light toward the sides to stay within those standards.
Side light has its benefits. "You’re more likely to see objects on the right side of the road," says Mark Rea, director of the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, N.Y.
But neither HID nor halogen lights may provide enough light down the road on their low beams, says Michael Flannagan, senior associate research scientist at the University of Michigan’s Transportation Research Institute. "Each year, some 2,300 pedestrians are killed at night in the road, not on the shoulder," says Flannagan, who analyzed 11 years of nationwide crash data to calculate the effect of darkness on pedestrian fatalities. His 2001 study found that pedestrians are killed at four times the rate in darkness as in daylight.
"The farther drivers can see straight ahead on low beams, the better," says Flannagan. We agree. Unfortunately, while many HID lights we tested were among the better performers, even the best didn’t outdistance the best halogens.
What we found. We compared 31 cars and trucks with halogen lights and 10 with HIDs, measuring their ability to light the road ahead and along the sides as well as checking them for glare (see
Headlight testing).
Six out of 10 vehicles with HIDs and 9 out of 31 with halogens reached the 400-foot marker on our test course with low beams, compared with an average of 335 feet for all models tested.
The farthest so far: the inexpensive, halogen-equipped
Mazda Protegé5. Its low beams illuminated our 600-foot marker without creating a glare problem.
Both types of lights produced our worst performers. The HID-equipped
Audi TT’s low beams lit only to our 200-foot marker, while the halogen-equipped
Chrysler Sebring and
Pontiac Grand Prix provided weak, nonuniform light.
Little room for error. While even 200 feet of lighting may sound like enough, it may not be. Based on typical reaction times and braking distances, drivers traveling at 50 mph need 237 feet to see a pedestrian, hit the brake pedal, and stop in time. Wet or icy roads and higher speeds increase braking distance, while fog, glare, and fatigue reduce visibility.
GLARE: WHY HIDs CAN CAUSE MORE
Ironically, the same attributes that tend to endear HID headlights to many drivers who have them can account for the lights’ added glare. The major ones:
That blue hue. Experts say that the blue-white tint of high-density discharge headlights can be uncomfortable for oncoming drivers. "The short wavelengths that make the light blue seem to be more glaring," says Rea. He adds that glare increases with age as eyes grow more sensitive to scattered light.
When side light shifts. An HID’s added side light can be a problem on winding roads as right curves aim that light at oncoming drivers.
More wet-weather glare. Added light directly in front of an HID-equipped vehicle can be reassuring from the driver’s seat. But lots of foreground light can also reflect off wet roads and up toward oncoming traffic, creating more glare for drivers coming toward you.
A sharper cutoff. HID headlights tend to define the top of their beams with a sharp horizontal line, compared with most halogens’ smoother fade to darkness. Bumpy roads can cause that sharp beam to flash at oncoming drivers and in the mirrors of cars ahead as it bounces in and out of view.
Glare can be a problem even on smooth, multilaned highways when HID-equipped SUVs are in the left lane. Our test staff found that the higher-mounted lights on those vehicles tended to accentuate HID lights’ sharp cutoff and wide right-side lighting, causing the light to shine directly into the mirrors of vehicles in the right lane.
A BRIGHTER COURSE
In a new nationwide NHTSA survey of 4,321 drivers, 30 percent of respondents found glare from headlights disturbing. "That’s a pretty good chunk," says Michael Perel, the NHTSA research engineer who ran the survey.
In January 2003, Perel told a conference of researchers that new rules may reduce the maximum height for all headlights. NHTSA may also require self-leveling, which adjusts HID beams based on load so they don’t point upward when the vehicle is full. Self-leveling is required in Europe, where HID headlights are currently on 25 percent of all vehicles.
What NHTSA can do. According to Flannagan of the University of Michigan, HID headlights have the potential to provide better forward visibility without more glare if their reflectors and lenses redirected some of the extra light. While the industry lighting engineers we spoke with acknowledged some challenges, they tended to agree.
We think NHTSA should take the following steps:
Require better lighting straight ahead for all headlight low beams.
Adopt the European standard requiring HID headlights to be self-leveling.
Require a smoother, more gradual low-beam cutoff for HID and other headlights to address a key source of glare.
Consider having carmakers chemically alter HID bulbs. Or use color-correcting lenses, which move an HID light’s white spectrum more toward yellow, like that of conventional halogen headlights.
Better control foreground light levels for HID headlights.
Reduce the maximum height of low-beam headlights on SUVs and pickups to make it more in line with the lights on lower passenger cars.
. WTF, compare some real HID cars like mercedes and BMW.
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