How Consumer Reports, The IIHS, And Others Test Car Headlights

While plenty of cars have headlights that are nothing short of retina-searing, you might be surprised to find that, according to the Insurance Institute for Highway Safety (IIHS), there are still new cars sold to the public with below-average headlight performance. Put simply, federal compliance, which is mandatory for all new cars sold, does not automatically translate to superior headlights. Independent testers like Consumer Reports (CR) and IIHS have their own way of testing headlights, which are often more comprehensive and place greater emphasis on real-world illumination and glare rather than simply looking at whether a lighting system meets the FMVSS requirements set by the NHTSA.

While CR utilizes both an indoor and outdoor approach, IIHS focuses on the latter. Within CR's dedicated windowless indoor facility is where the lights are aligned and tested for the presence of stray beams, which, depending on how much there is, can affect bad weather visibility. The test then proceeds outdoors, where testers first turn on the low beams and then switch to high beams to check whether they can spot the many obstacles (painted in black) dotted around the test track. Performed on a dark, moonless night, the testers jot down their observations of both the low and high beams, taking into account their reach, intensity, and how wide and even the beam patterns are.

IIHS, on the other hand, tests cars in their "as received" condition, meaning they're not adjusted for aim. Unlike CR's test, which is predominantly done when the car is stationary, IIHS dynamically checks low and high-beam performance by subjecting the vehicle to a series of turns and then evaluating them accordingly. Testers use a five-approach setup—consisting of a straightaway, gradual left-right curves, and sharp left-right curves—to see how far the beams (at 10 inches above the ground) can successfully light the road ahead with an intensity of at least five lux. Each route is driven six times in total with both low and high beams. In other words, that'd be three runs on the straightaway with the low beams turned on and three with the high beams, repeating the same process for the rest of the four approaches. Glare from the low beams is measured at three feet seven inches above the road, according to the IIHS.

Headlight systems are then rated (either good, acceptable, marginal, or poor) based on the demerits they receive, which include illumination shortfalls and glare performance, with good- and poor-rated headlights featuring the least and most demerits, respectively. Both CR and IIHS insist on straightaway illumination being the most important, as it offers a buffer, allowing the driver to better judge and react to obstacles on the road.

Something else that may be of interest is how Headlight Revolution tests the many aftermarket headlights they sell. Although you could point to a conflict of interest, in that Headlight Revolution is owned by the same group that owns Morimoto and GTR Lighting (among other brands), the tests conducted seem thorough and objective.

The multi-point testing system, as it's called, considers eight specific points across the light pattern to gauge low and high-beam performance. The YouTube video explains that points one through six are for the low beams, measuring how far, wide, and visually comfortable they are, while points seven and eight measure the high beam's distance, reach, and foreground illumination after converting the wall results to a road simulation.

It also helps to understand that because the overall scores are a summary of how the lights function across the various test points, seeing two headlights with similar overall scores doesn't mean they have similar performance. According to the video, these eight points are a condensed version of the many regulatory lower beam (LB) and upper beam (UB) requirements set up by the NHTSA. To know whether the high beams are brighter than the minimum legal requirement of 40,000 candela, the test has something called the merit system, where a merit score of 1.0 indicates 40,000 candela and 1.9 (the maximum value) corresponds to 75,000 candela, which is the legal threshold, implying that it's about 90% brighter than the minimum requirement. Keep in mind that although DOT-compliant aftermarket headlights are a thing, drop-in LEDs for halogen lights aren't.