I bought them anyway but this is what my Optometrist told me. They won't really darken in the car because the UV rays have to hit the lenses and the car's windows block most of them. Second was that in hot weather they aren't as effective as cold weather as temperature has a big influence on how much they change and the biggest complaint in northern climates is they get too dark. In my experience they don't get dark enough in summer or winter and are too slow to change when walking into a building.
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Les
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