I have a very good-fitting pair of Tifosi glasses that darken and lighten rapidly when the light changes. They do a great job of keeping cooties out of my eyes, too. I also wear them indoors when I have migraines, and they do lighten enough indoors that I can see just fine.

http://www.rei.com/product/751877

Love these glasses! If I lost them, I'd go right out and buy another pair.