Pit Viper 2000s Cosmos Photochromic 2000 Black Sunglasses have a coating that responds to UV light. When out in the sun, they'll get darker, and the lens will lighten without UV exposure. Check your local UV index with these babies - the higher your UV index, the stronger these will respond. Only true-blue UV light triggers the reaction so wearing these in your car, or indoors, while stylish, won't have the reactive flair. 

UVA & UVB Protection: 100%
Visible Light Transmission: 87-17% VLT
VLT Ideal Performance Zone: 60-25% VLT
Lens: 1.2mm Polycarbonate Smoke Photochromic Lens
Polarized: No
Frame Width: 5.66in (Merika)/ 144mm (Metric)
Frame Height: 2.34in (Merika)/ 59.5mm (Metric)
Nose Opening: 1.31in (Merika)/ 33.5mm (Metric)