IIHS tests headlights; only Prius v earns 'good' rating [Video]

Midsize cars from BMW and Mercedes-Benz all received \'marginal\' or \'poor\' ratings.

The Insurance Institute for Highway Safety's first-ever headlight tests have resulted in just one 'good' rating from a field of 31 midsize vehicles with 82 different headlight configurations.

The Toyota Prius v was the only car to receive a 'good' mark, and only when equipped with the Advanced Technology Package at the highest trim level -- $8,400 above the base price.

The IIHS placed light sensors along its test track to evaluate low- and high-beam performance on five different approaches: straight, sharp left/right turns and gradual left/right curves. Results for low beams are weighted more heavily, while headlights with too much glare cannot earn a rating above 'marginal.'

"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," said IIHS senior research engineer Matthew Brumbelow. "In contrast, someone with the halogen lights would need to drive 20 mph slower in order to avoid a crash."

At the other end of the spectrum, the halogen lights on the BMW 3-Series were deemed the worst among 44 headlight systems to earn a 'poor' rating. A driver would have to be traveling no faster than 35 mph to stop for an obstacle in the travel lane. BMW's upgraded LED curve-adaptive lighting is better, but not good enough to earn above a 'marginal' score.

Other cars in the 'poor' category include the Buick Verano, Cadillac ATS, Chevrolet Malibu, Hyundai Sonata, Kia Optima, Nissan Altima, Volkswagen Passat and Mercedes-Benz C-Class and CLA.

"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," concluded IIHS chief research officer David Zuby.