LED headlights found in 31 different midsize car models evaluated delivered a relatively mediocre performance out in the first headlight ratings conducted by The Insurance Institute for Highway Safety in the U.S.

Recent advances in headlight technology make it a good time to focus on the issue. In many vehicles, high-intensity discharge (HID) or LED lamps have replaced halogen ones. Curve-adaptive headlights, which swivel according to steering input, are also becoming more widespread.

Research has shown advantages for the new headlight types, but they don't guarantee good performance. The Institute's headlight rating system doesn't favor one lighting technology over the other, but simply rewards systems that produce ample illumination without excessive glare for drivers of oncoming vehicles.

The Toyota Prius v’s LED projector low and high beam headlights earned the only good rating out of all 31 car models evaluated.

The best available headlights on 11 cars earn an acceptable rating, while nine only reach a marginal rating. Ten of the vehicles can't be purchased with anything other than poor-rated headlights.

A vehicle's price tag is no guarantee of decent headlights. Many of the poor-rated headlights belong to luxury vehicles.

One good rating out of 82

Vehicles can be equipped with different headlights, so there are a total of 82 headlight ratings for 2016 models even though there are only 31 vehicles. The Institute is rating every possible headlight combination as it becomes available from dealers.

The Prius v earns a good rating when equipped with LED lights and high-beam assist. To get those headlights, consumers must purchase the advanced technology package, which is only available on the highest trim level. When equipped with regular halogen lights and without high-beam assist, the Prius v earns a poor rating.

"The Prius v's LED low beams should give a driver traveling straight at 70 mph enough time to identify an obstacle on the right side of the road, where the light is best, and brake to a stop," says Matthew Brumbelow, an IIHS senior research engineer. "In contrast, someone with the halogen lights would need to drive 20 mph slower in order to avoid a crash."

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.

Curve-adaptive systems don't always lead to better ratings. The Cadillac ATS, Kia Optima and Mercedes-Benz C-Class all earn poor ratings even when equipped with adaptive low and high beams.

In the case of the Optima, a big problem is glare. Its curve-adaptive system provides better visibility than its non-adaptive lights, but produces excessive glare for oncoming vehicles on all five low beam approaches.

One of the best headlight systems evaluated has none of the new technology. The basic halogen lights on the Honda Accord 4-door earn an acceptable rating, while an LED system with high-beam assist available on the Accord earns only a marginal rating.

LEDinside breaks down LED headlight performance in IIHS Study

Of the 24 car models offering LED headlights tested, nearly 45.83% (11 car models) received marginal rating, followed by 28.17% (7 car models) that were given an acceptable rating. LEDs headlights outperformed halogen lights, but ratings indicated HID headlights delivered slightly more reliable performance. This suggests LED headlight performance is somewhere in the middle, and has room for further improvement.

Only the Toyota Prius V LED headlight was given a good rating review, while four car models including luxury car brands BMW 3 series, Audi A3, 2016 Lexus ES 350 and 2016 Mercedes C-Class were given poor ratings. The BMW 3 series and Audi A3 headlights used LED reflector designs, while Lexus and Mercedes C-Class headlight designs were LED projectors.

In general, Japanese car brands LED headlights received better review ratings than German luxury car brands in this study.

(Source: IIHS)

So how does LED lighting technology compare to traditional automotive lighting? Overall, LED headlights outperformed halogen headlights, which received the worst ratings out of all three headlight technologies combined. Of the 35 halogen headlights tested about 85.17% received a poor rating, four headlights received a rating of marginal and only one headlight option from 2016 Subaru Outback passed with acceptable.

But when compared to HID headlight technology, LEDs are still lagging slightly behind. Of the 24 HID headlights tested, 33.33% (8 HID models) received ratings of acceptable, another third of the headlights were rated as poor, and 29.17% (7 HID models) performance was marginal.

According to IIHS, The ability to see the road ahead, along with any pedestrians, bicyclists or obstacles, is an obvious essential for drivers. However, government standards for headlights, based on laboratory tests, allow huge variation in the amount of illumination that headlights provide in actual on-road driving. With about half of traffic deaths occurring either in the dark or in dawn or dusk conditions, improved headlights have the potential to bring about substantial reductions in fatalities.

For further information on the research method the institute used to evaluate the headlights please see here.