headlights are much much brighter than the sun so tinting be highly activated at night.

Cadillac used to have a thing that detected approaching headlights and turned off your high beam automatically. Don't know whether it worked.

Having worn photogray lenses for years I can assure you that a photochromatic windshield is not something you want. The first time you drive into a parking garage, tunnel, or storage building you'll know why. At least with my glasses I could look over the tops until they readjusted. You can't do that with a windshield.

http://www.whynot.net/ideas/4131#comment-14600

i agree that this would not work, because of the adjustment time upon entering any indoor structure or tunnel, but headlights would not effect the tint, because all modern photo-chromatic lenses react to the sun's u-v light and not visible light, this is why the "transitions" lenses do not work inside a vehicle, a common complaint, because the normal glass blocks out the u-v.

Great idea! I love my photochromic glasses and think it would be wonderful for car windows. You never tint windshield glass (except at the top), so that's not a concern. Like my glasses, the windows would not be the right tint 100% of the time, but a larger percentage of the time than either static option.

I think the commenters here are reading too much into the idea. On any given car with tinted windows, the one place you don't have a tint is the front windshield. I don't see anything in the post that suggests tinting the front windshield (which would be dangerous and illegal whether it was 'transistions' tint or regular tint).

I suppose though you could use a 'transistions' approach in that small strip at the top of the windshield which is sometimes additionally tinted but it would be just as easy (and cheaper), to use regular methods.

I actually think for side/back windows this would be kind of nice. During a sunny day you want tinting, but at night I wouldn't mind having clearer windows for greater visibility. As for how something like this would react to headlights/streetlights I couldn't say.