PHOTOSUN XDF Photochromatic sunglass lenses react automatically to sunlight. On overcast days lenses are a medium to light sunglass tint, On sunny days PHOTOSUN XDF lenses are dark. PHOTOSUN XDF is a registered trademark of Corning Inc. These lenses meet ANSI-z80.3 special purpose UV Requirements, block 100% of UVB and 99% of UVA harmful Ultra Violet Rays. Please note that, photochromatic effect is very subtle.