Are your headlights doing the job? Probably not, says auto safety study.

A nonprofit that tests cars for safety for the first time tested headlights. It found that the lights on only one of 31 midsize cars are up to snuff.

For people who struggle to see while driving at night, the Insurance Institute for Highway Safety has found that the problem is likely not you: it’s your car.

"If you're having trouble seeing behind the wheel at night, it could very well be your headlights and not your eyes that are to blame," David Zuby, executive vice president and chief research officer at the institute, and industry trade group that tests and rates car safety, said in an announcement.

For the first time ever, the nonprofit that regularly tests cars for crash safety has tested the headlights of 31 midsize 2016 cars and found that only one, the Toyota Prius V, has “good” headlights. This means, for example, that its headlights were able to illuminate a straight road well enough for the driver to see a pedestrian, bicyclist or other hazard up to 387 feet ahead. At that distance, the vehicle could be traveling up to 70 miles per hour and still have time to brake.

Among the lowest-rated headlights were the ones on the BMW 3 series, which were able to illuminate only 128 feet ahead, reports The Associated Press. In order to stop for a pedestrian in time, the driver would need to be traveling under 35 miles per hour.

Overall, the headlights on 11 cars (including Audi A3, Nissan Maxima, and Volvo S60 ) were rated “acceptable,” on nine cars (including Acura TLX, BMW 3 series, and Subaru Legacy) they were rated “marginal,” and on ten cars (including Buick Verano, Cadillac ATS, and Kia Optima) they were rated “poor.”

The institute’s ratings are based on a series of tests that measured the light from both low beams and high beams while the vehicles were driven on a test track at night. The testers drove them straight, in a sharp left curve, a sharp right curve, a gradual left curve and a gradual right curve. They also measured the amount of glare the cars cast on oncoming vehicles.

“We found the same light bulb, depending upon what reflector or lens it's paired with and how it's mounted on the vehicle, can give you very different visibility down the road," Mr. Zuby told the AP.

There was no winning lighting technology, the institute found. Whether carmakers used LED lights or halogen, high-beam assist or curve-adaptive headlights – which pivot in the direction the car is turning – did not determine how well the cars performed. The more expensive cars didn’t perform better either.

Even the star performer, the Prius V, rated well only with the LED lights and high-beam assist, a technology that automatically turns high beams on and off as it senses if other cars are around. But that lighting combination comes in a premium package that consumers have to purchase separately. The basic Prius V equipped with halogen lights and without high-beam assist received a poor rating by the institute.

This would imply that a more expensive package with LED lights is better, but that’s not necessarily true. While the Prius V LED headlights package rated highly, the same combination in a four-door Honda Accord – LED lights with high-beam assist – were rated as only acceptable. And while the Prius with the halogen lights rated as poor, and the BMW Series 3 marginal, the four-door Honda Accord with halogen lights rated as acceptable.

“Just looking for the LED lights wouldn’t guarantee that you have a good-rated vehicle,” Matthew Brumbelow, a senior research engineer at the institute, told The Christian Science Monitor in an interview. “There are so many things that go into designing a good headlight,” he said.

Headlight-related visibility is not regulated by the National Highway Traffic Safety Administration, which makes vehicle safety rules.

The nearly 50-year-old federal standard for headlights is based on how much light comes out of the light source, not on how the light is projected down the road, as the AP reports.

With about half of traffic deaths happening either in the dark, in dawn, or dusk conditions, says the institute, it’s time to upgrade headlights.

“Up until now, [car] manufacturers didn't have a visibility metric,” says Mr. Brumbelow. “What we’re hoping is that by giving them this new metric, this new target to shoot for, that it will improve visibility of headlights across the board,” he says.

The institute will do regular headlight testing from now on and is already testing SUVs and pickup trucks, the ratings for which will come out later this year.