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A Dim View: Only 1 Car Out Of 31 Is Deemed To Have 'Good' Headlights

By Bill Chappell

Published March 30, 2016 at 9:44 AM EDT

Do you see the deer? A Honda Accord four-door with halogen lights (left) was found to have "acceptable" lights, while the Mercedes-Benz C-Class, also with halogen, was given a "poor" rating, based in part on how well each car lit objects on a straight section of road.

If you're driving a Toyota Prius V outfitted with LED lights, you can breathe a sigh of relief: According to a new study of car headlights, it's the only midsize vehicle to get the top rating of "good" in a study of how 31 different cars light the road at night.

In all, the Insurance Institute for Highway Safety tested 82 different headlight configurations available on 2016 model-year cars. More than half of these setups (44) earned no better than a rating of "poor."

Researchers found that cost — and even high-tech promises of seeing around curves — had little to do with performance. BMW, Mercedes-Benz and Cadillac were all found to have poor headlight options.

From the study:

"Among the 44 headlight systems earning a poor rating, the halogen lights on the BMW 3 series are the worst. A driver with those headlights would have to be going 35 mph or slower to stop in time for an obstacle in the travel lane. A better choice for the same car is an LED curve-adaptive system with high-beam assist, a combination that rates marginal."

In at least one case, a basic light package tested better than pricier options. That's true for the four-door Honda Accord, which lit the road more effectively with halogen lights than with an optional LED system with high-beam assist, the IIHS says.

You might be wondering, as we did, if the ratings simply favor glaringly bright lights that could also create a hazard for drivers of oncoming vehicles. The IIHS says it also thought of that, giving demerits to cars deemed to cause excessive glare.

The group singles out the Kia Optima for glare, saying that while the car's curve-adaptive system gives Optima drivers better visibility, it also "produces excessive glare for oncoming vehicles on all five low beam approaches."

To conduct the study, IIHS researchers tested midsize cars on a track after dark, measuring how well the vehicles' lights illuminated the path ahead under five different circumstances: traveling straight, sharp curves to the right and left, and gradual curves to the right and left.

In addition to flagging problem areas, the study also suggested possible solutions.

"Many headlight problems could be fixed with better aim," says IIHS Senior Research Engineer Matthew Brumbelow. "This is simple enough to adjust on many vehicles, but the burden shouldn't fall on the consumer to figure out what the best aim is. Manufacturers need to pay attention to this issue to make sure headlights are aimed consistently and correctly at the factory."

Its researchers didn't adjust or retune the cars' headlights, the institute says, because most car owners don't do that, either — and because some carmakers advise against it.