The Insurance Institute for Highway Safety (IIHS) tested all of the headlight configurations available on 31 midsize cars. The results were abysmal. Despite much of the new technolgy for headlights, IIHS found that the light intensity at long distances and glare of an oncoming vehicle to be less than ideal. All but one of the 82 vehicle and headlight combinations tested received marginal or poor ratings. Only one received a good rating.
Only the Toyota Prius v is available with a headlight system that earns a good rating from IIHS. The best available headlights on 11 cars was just an acceptable rating. Nine of the cars surveyed only achieved a marginal rating, and ten do not come with anything other than poor-rated headlights. IIHS found that a vehicle’s price tag is no guarantee of decent headlights. Many of luxury vehicles had the poor-rated headlights. For example, the tests found that the BMW 3 series had the lowest-scoring headlight system.
“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,” said David Zuby, IIHS executive vice president and chief research officer.
IIHS asserts that government standards for headlights, based on laboratory tests, allow huge variation in the amount of illumination that headlights provide in actual on-road driving. The institute says that about half of traffic deaths occur either in the dark or during dawn or dusk conditions. Therefore, improved headlights could potentially reduce driving fatalities substantially.
In many vehicles makes and models, high-intensity discharge (HID) or LED lamps replace halogen ones. Curve-adaptive headlights, which swivel based on the direction of the steering wheel, also are becoming more widespread. IIHS and HLDI research shows that curve-adaptive headlights are improving visibility and reducing crashes.
IIHS evaluated the headlight performance on the track after dark at the Vehicle Research Center in Ruckersville, Virginia. They used a special device to measure the light from both low beams and high beams as the vehicle takes five different approaches: traveling straight, a gradual left curve, a gradual right curve, a sharp left curve, and a sharp right curve.
IIHS Senior Research Engineer Matthew Brumbelow examined statistics related to real-world nighttime crashes to determine the shape of the test curves and how much weight that each test portion should carry.
To assess visibility, Brumbelow and other VRC engineers measured how far the light is projected so that it measures at least 5 lux.
The test also measures glare from low beams in each scenario to ensure that it isn’t excessive.
Most vehicles allow adjustment of the vertical aim of headlights. However, IIHS says that proper aiming of the headlights should be done at the factory and not left up to consumers. For this reason, IIHS tests headlights as they are received from the dealer.
A car’s pitch changes as it moves, affecting headlight beam angle and making illumination difficult to measure.
IIHS engineers created a sensor tree to take multiple light readings that adjust to show what would happen on a perfectly flat road at a constant speed. This allows vehicle testing comparisons even if tests are performed in different locations
The IIHS tests compare the visibility and glare measurements to a hypothetical ideal headlight system, and the tests use a scheme of demerits to find the rating. The tests weigh the results from low beams more heavily than high beams because they are used more often. The readings on the straight areas are weighted more heavily than those on curves because more crashes occur on straight sections of road. A vehicle with no demerits doesn’t exceed the low-beam glare threshold on any approach. It must provide illumination to at least 5 lux over specified distances, ranging from nearly 200 feet for low beams on a sharp curve to nearly 500 feet for high beams on the straightaway.
Vehicles equipped with high-beam assist that automatically switches between high and low beams depending upon whether or not other vehicles are present, may earn back some points taken off for less-than-ideal low-beam visibility. The tests only give this credit for approaches where the glare threshold isn’t exceeded and where high beams improve visibility compared with low beams.
Excessive glare on any approach earns a vehicle a marginal rating at best. Out of 82 possible headlight configurations that are available for the 31 vehicles, only one configuration on one vehicle was found to be good. The Prius v earns a good rating when it is equipped with LED lights and high-beam assist. The good headlights on the Prius v only come with the advanced technology package, which is only available on the highest trim level.
The low beams on the Prius v with this configuration reach a distance of almost 400 feet in the right lane while traveling straight and about 160-210 feet on the curves. The high beams extend over 500 feet on the straight sections and about 180-220 feet on the curves. Neither the low beams nor the high beams are curve adaptive. According to IIHS, the Prius v’s headlight performance on curves might be improved if that feature was added.
However, use of regular halogen lights on the Prius v without high-beam assist earns a poor rating. The tests found that the halogen lights on the BMW 3 series are the worst, and IIHS found that the Cadillac ATS, Kia Optima and Mercedes-Benz C-Class all earn poor ratings, even when equipped with adaptive low and high beams.