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Status Report, Vol. 49, No. 7 | October 9, 2014 Subscribe

Adaptive headlights help drivers spot objects earlier; glare not excessive

Headlights that swivel around curves in response to steering input allow drivers to spot a hard-to-see object on a dark, curvy road about a third of a second earlier than they would with conventional headlights, a new IIHS study has found.

The experimental study of adaptive headlights was conducted with volunteer drivers on a rural road near the Institute's Vehicle Research Center in Ruckersville, Va. It compared drivers' ability to spot objects on the roadside in vehicles with fixed halogen headlights, fixed high-intensity discharge (HID) headlights and adaptive HID headlights. The results suggest that HID lights, whether fixed or adaptive, have a small advantage over halogen ones, and adaptive HID lights improve visibility over either type of fixed headlight.

HID lamps began appearing in luxury vehicles in the 1990s and have gained popularity because they improve visibility by casting a whiter light and illuminating the driver's peripheral field more than halogen lamps. Adaptive headlights were first introduced in the 2004 model year. As of the 2014 model year, they were standard on 14 percent of models and optional on 22 percent.

Earlier research by HLDI showed that vehicles equipped with optional adaptive headlights had lower rates of insurance claims under most coverage types than the same vehicles without the technology (see Status Report special issue: crash avoidance, July 3, 2012). The benefits were greater under property damage liability insurance, which covers damage to someone else's vehicle or other property, than they were for collision insurance, which covers damage to the insured vehicle. Injury claim rates also were lower.

"We already had evidence that adaptive headlights are reducing crash damage and injuries," says David Zuby, IIHS executive vice president and chief research officer. "This study fills in some of the gaps in our knowledge about how they help."

In the IIHS study, 20 volunteers drove a pair of 2013 Mazda 3 small cars. One car had adaptive headlights with HID bulbs. The adaptive lighting system could be turned off, making the headlights fixed HID lights. The second vehicle had fixed halogen lights.

Each participant drove an 8-mile round trip with each of the three types of headlights. The driving was done at night on a two-lane road with no markings. Aluminum targets, measuring 8 by 12 inches, were placed at various locations on the side of the road. Half of the targets were highly reflective, and half were less reflective. As they drove at 30 mph, the drivers were tasked with pushing a button each time one of the targets came into view.

With adaptive headlights, the drivers spotted low-reflectance targets located inside of curves as much as a third of a second earlier, or about 15 feet sooner at 30 mph, than with regular headlights. Response times also were shorter for low-reflectance targets on the outside of curves, but these results weren't statistically significant. As expected for a system designed to help drivers negotiate curves, there was no difference between adaptive and fixed headlights when the targets were on straight stretches of road.

HID lamps also appeared to help visibility even when they were fixed. In this case, the benefit was seen with high-reflectance targets on straight sections of road. HLDI's 2012 analysis of Mercedes-Benz features also indicated a benefit from fixed HID over halogen lamps. Together these observations indicate that the advantage of adaptive systems is partly due to their steerability and partly a result of using HID instead of halogen lamps.

When it comes to improved headlight systems, it's important to consider how changes affect other drivers on the road. The IIHS researchers conducted a separate study to compare the glare from the Mazda's halogen, fixed HID and adaptive HID headlights. The 20 volunteers were asked to rate the glare from approaching vehicles on a scale of 1 to 9, with 1 being unbearable and 9 barely noticeable. They also rated a fixed high-beam headlight system to serve as a benchmark for excessive glare.

Participants rated the HID low beams as slightly more glaring than the halogen lamps, but neither was excessively glaring. There was no difference between adaptive HID low beams and fixed HID low beams. Measurements taken from light meters located near the participants supported their subjective ratings.

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