On Tuesday, the Associated Press ran a story that seemed sure to bring relief to an aggrieved group of Americans: those of us being blinded by headlight glare.
“General Motors is recalling more than 740,000 small SUVs in the U.S. because the headlight beams can be too bright and cause glare for oncoming drivers,” the story begins. The recall in question involves the GMC Terrain, model years 2010 to 2017.
For we squinting few who maintain that an epidemic of headlight blinding is underway, this news seemed most welcome. The idea that almost a million SUVs have been found to be too bright for the road—well, that was proof we weren’t crazy. And the idea that they would now be asked to dim their lights? A gentler nighttime driving experience was on the way.
Unfortunately, a close reading of the National Highway Transportation Safety Administration’s notice on the subject shows that this isn’t quite what’s happening here. The Terrain’s headlights are getting pulled for a weird glitch that causes them to shine brightly to the side of the car, at up to a 45 degree angle. That is the context in which the Terrain’s headlights are “three times too bright.”
At that angle, GM argued, the stray bright reflection couldn’t really blind anyone except in conditions of snow or fog. NHTSA doesn’t really seem to disagree, though it ordered the company to fix the problem anyway.
The upshot, basically, is that these were not the blinding headlights we were looking for.
Let’s back up a little bit: For some time, some American drivers have been convinced that an epidemic of headlight-induced blindness is underway on the roads. The journalist Jack Crosbie made the definitive remark on the crisis last year, when he wrote:
This may sound like a simple gripe, but something is happening. When I wrote about this topic in 2018, John Bullough—now a director at the Light and Health Research Center at Mount Sinai Hospital in New York—told me there were three things going on. SUVs and pickups have taller bodies and therefore higher lights that are more likely to shine in your eyes if you’re in a lower car or on foot. Bluer LED headlights, common on newer cars, feel brighter to many people. And some state vehicle inspections don’t even try to adjust the position of headlights, which tend to get bumped out of whack after a couple years of driving.
Since then, the share of SUVs and trucks on the road has continued to increase, which means more headlights that are more likely to shine in people’s eyes.
The share of LED headlights is up too. Though they can easily be filtered (by manufacturer or buyer) to look warmer and yellowed, these usually have a bluer tinge than earlier generations of headlights. LED headlights are subject to the same brightness rules as regular headlights, but many people insist they seem brighter. Including the drivers who keep buying them for that reason.
Mark Rea, a light scientist at Mount Sinai in New York, explained why that might be. Headlights are measured in lumens, a unit devised to assess how light impacts a central part of the eye. But that part of the eye, Rea observed in a 2015 paper, is more sensitive to higher-wavelength, redder light than lower-wavelength bluer light. The very measurement system we use to calibrate headlights (and everything else) is not counting blue light, and so bluer lights will have to feel significantly brighter before they register as equal in lumens.
“Imagine a car with two headlights, one halogen, one LED. They’d both meet the requirements. The light meter would say they’re the same, but the LED would look 40 percent brighter,” Rea said. This is also why neighbors complain about LED street lamps—the lamps may have the same lumen measurement, but the LEDs really are brighter. “This has implications for glare, energy efficiency, and safety, all based on something some guys came up with in the 1920s. They’re measuring light inappropriately.”
The growing availability of LED headlights will, in the end, be good news for drivers coming face to face with pickups at night. That’s because the bipartisan infrastructure bill passed last year requires regulators approve a technology called “adaptive driving beam” headlights by 2023. Adaptive driving beam headlights use software-enabled LEDs that adjust the headlight beam to avoid other drivers and illuminate your surroundings.
That will mean an end to headlight glare for drivers on the road as it slowly fills with new cars that adopt this tech. (And new cars probably will adopt this tech—in addition to helping those around you, it will help you see much better at night.) As for pedestrians … they will be more brightly, blindingly lit than ever. Better blind than dead, I suppose.
This article has been updated with comments from Mark Rea.
