Analysis by Daniel Stern, DVN Chief Editor
A lighting non-expert sent me an e-mail a few months ago, and shared his pet theory with me: noncompliant headlamps are rampant on American roads, he said; they put out many times more glare than is allowed. He’d found a photometric table from FMVSS 108 and interpreted it as limiting maximum intensity to 20,000 cd anywhere in the beam, and because he’s seen readings much greater than that with his handheld light meter, he is sure new vehicles are coming with illegal headlamps. Automakers are cheating, he says, just like they did in Dieselgate, and nobody’s stopping them.
Over the course of 22 emails, I did my best to educate the guy. I sent him scads of relevant research and explained it to him. I showed him how to correctly interpret the photometric tables. I answered many questions: yes, headlight glare is real. No, it’s mostly not caused by the light colour. Yes, we have a self-certification system in America. No, that doesn’t mean automakers are just doing whatever they want and lying about it. No, noncompliant headlamps are almost nonexistent on new vehicles. Yes, the real main cause of headlight glare on the road really is misaim.
He doesn’t believe me, and so he set out to ‘prove’ himself right (and me wrong) by ‘measuring’ the headlamps on cars he finds especially offensive, like the Tesla Model 3. Those words are in sneer quotes because he’s waving a handheld luxmeter around in front of randomly-aimed lights on a random car on a random road. I explained goniophotometry, and his response was “Goniometer is just another word for a protractor; you can buy them for seven dollars. FMVSS 108 doesn’t require a photogoniometer, so I’m using trigonometry to know where to put the luxmeter, and I’m measuring 3 to 10 times the so-called glare limit, there’s no way that’s just an error caused by my technique”. Oh…boy. That density of misinformation requires something like a diamond-tipped drill bit to penetrate, and even then there’s no guarantee. I had to give up.
So why did I give him so much time and effort? Why did I even bother replying in the first place? Partly in hopes he’d see the light, if you’ll excuse me for putting it that way, and partly in penance for having run my own mouth at high volume decades ago as a 20something when I thought I knew it all about headlights, but what I really had were pet theories, guesses, preferences, and opinions—they certainly felt like knowledge to me! With a great deal of studying I replaced ignorance with knowledge, and now I try to pass that along where and when I can.
But this particular guy has chosen to carry on in his ignorant certitude. He’s sure he’s found a vast glare-conspiracy, and he’s found a comfortable echo chamber (with chapters in America and Britain, as described in DVN previously). I guess in his mind I’m in on the conspiracy. A pity, because now he’ll join the other loud nuts and nitwits in poisoning any chance of really getting headlight glare under control on this continent through legitimate technical-legislative-regulatory channels. And that leaves illegitimate channels for dealing with it, such as the glare-revenge device I reported on in these pages nearly a decade ago.
Where does that trend end, then? That’s an uncomfortable question to ask about the United States, where people get shot to death for perceived offences much smaller than headlight glare.
