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.