TECH: Who Decides How Much Glare From Headlights Is Too Much?

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Headlight glare is now in the spotlight. The group who decides how much is too much picked an interesting way to decide where that line is.

headlight engineer IIHS

Headlights are starting to be phased into the safety scores consumers and automakers rely upon to gauge how safe a vehicle is compared to its peers in a segment.

The Insurance Institute for Highway Safety (IIHS) is now testing and ranking all the headlight systems available on the most popular-selling models.

In a recent round of IIHS testing, 17 of 42 headlight systems on small crossovers had excessive glare.  Three models were rated Poor based on headlight glare alone. The interesting thing about the glare ratings the Institute is compiling is that it isn’t an expert at the laboratory that decided how much glare is too much. It was you, the average driver.

headloght glare graph iihsOf course, there are ways that scientist and engineers can measure glare.

However, IIHS knew that there was a need for real people to be involved in its testing and to set the point at which glare is considered too much. What IIHS came up with was a group of 20 individuals, ten men and ten women who would be the glare jury. The qualifications for the participants are real-world sensible.

Everyone considered had driven at least ten years, was between 30 and 50 years of age, and had a relatively clean driving record. Of course none had night-time restrictions on their license. Also, so that the Institute could be certain it didn’t pick any “ringers” form its own scientific community, it used a third party, the Chesapeake Institutional Review Board, to review its protocols for selection. Once the type of participant was profiled, the actual twenty were found through print and radio advertisements. Those chosen were paid a nominal $75 fee for their time.*

headlight rankings small suvs 16 IIHS

With about 400 U.S. vehicle models in a given year, some with up to three separate headlight systems, and with ratings to be refreshed every time a model changed its headlight design, using humans to judge every single vehicle tested would be cost prohibitive and a logistical nightmare. So instead of having humans judge each car, the Institute used the 20 to instead calibrate a set of instruments it developed.

The most recent testing for headlight effectiveness covered the compact crossover class. The Mazda CX-3 scored highest and had no problem with glare.

The apparatus measures glare using a metric called the DeBoer scale. This complex scientific method to determine glare levels was initially developed for streetlights and is now used widely as the measurement metric for glare in general. Using a 9-point scale, the DeBoer scale rating counts down from 9, rated “Just Noticeable” and ends with a score of 1, considered “Unbearable Glare.”

In its first test group of tested vehicles, IIHS found that the best headlights were not on expensive models, but affordable ones. This will now drive automakers to develop headlight systems that work better in the real world. Even better, the new systems won’t be blinding us as we see them approach.

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*Source: Test Track Evaluation of Headlight Glare Associatedwith Adaptive HID, Fixed HID, and Fixed Halogen Low Beam Headlights, IIHS, Oct. 2104, Ian J. Reagan, IIHS, Tim Frischmann, University of Central Florida, Matthew L. Brumbelow, IIHS