Here's what other sites are saying:
Photochromic construction allows the lenses of the POC Eye Do Sunglasses to change tint to match the light intensity in your surrounding environment. For exmaple: in your buddy's dingy basement 'suite,' the lenses in these massive shades would be lighter. Step out into the sun on a bright day (it's scary, we know) and the crystal-clear NXT lenses automatically darken. Although you could chalk the process up to voodoo, it's actually sciencejust like the grippy construction of the Hytrel nose and arm pads. See, the Do shades prove that science is cool.