Photochromic sunglasses automatically change color based on light conditions, letting more light in during dark, low-light conditions and blocking more light when it's bright and sunny. Look at the visible light transmission, or VLT, range for the glasses. Photochromic glasses are useful for sports where light conditions can change quickly; look for glasses with shatterproof, polycarbonate lenses for sport use. Flexible metal or plastic frames will also offer good durability for sport use. Make sure that the glasses fit comfortably on your face, are secure on the nose and cover your eyes from different angles. Polarized photochromic lenses will help against glare from water, snow and ice. You want glasses that block 100 percent of UV rays.

Many photochromic lenses do not work through car glass, so they aren't an effective option for the changing light conditions present while driving. If you need photochromic lenses for driving, shop for a pair that is designed for driving use. If you're looking for a pair of glasses for more reliable, steady light conditions, as in lying out on the beach, you'd be better off with a pair of dark lenses as opposed to a photochromic pair.

Not all sunglasses manufacturers offer photochromic lenses. A few prominent brands that offer photochromic glasses include Zeal, Oakley and Ryders. Shop for these sunglasses at a sunglasses store or sporting goods store. For eyeglass wearers, photochromic lenses that switch from clear eyeglasses to darkened sunglasses are available. Check with an eyewear store about this option. Online, you'll find photochromic options from retailers like REI and Sunglass Hut.

Photochromic lenses are a feature that typically isn't found on low-end sunglasses. Sport sunglasses with photochromic lenses are likely to run between $100 and $300. Ryders is a company that sells solid sports sunglasses for a lower price, offering a number of photochromic glasses for $50 to $80.