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Why are headlights getting brighter? Isn't their brightness regulated? It's getting to the point that if a pickup truck (by the way, why are cars getting bigger too?) is passing me, I will often hold up my left hand to shield my eyes.
Yes. The regulations can be found at this link—CFR title 49 section 571.108.S10, in the FMVSS. For example, if you want to find the requirements applicable to replaceable bulbs in a two-lamp system with mechanical aiming, check out the LB2M section of table XIX-a.
In the range 10 ° up to 90 ° up and 90 ° left to 90 ° right, the intensity must be no more than 125 candelas.
At the point 4 ° up and 8 ° left, the intensity must be at least 64 cd.
At the point 2 ° up and 4 ° left, the intensity must be at least 135 cd.
In the range 1 ° up and 1.5 ° left to [90 °?] left, the intensity must be no more than 700 cd.
In the range 0.5 ° up and 1.5 to [90 °?] left, the intensity must be no more than 1000 cd.
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You might start here.
"The trend toward improved headlight illumination has been fueled in part by manufacturers seeking higher safety ratings from the Insurance Institute for Highway Safety, Professor Kennedy said."
Yes, but policing of headlights is pretty unusual.
Safety ratings may also play a role here, but emissions laws that exempt larger vehicles have recently been blamed as well.
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