Revision Eyewear's Photochronic Hellfly Ballistic Sunglasses darken to a sunglass tint when exposed to sunlight and return to their clear state in the absence of UV rays. In tests, Revision's Photochromic Hellfly lenses took only 45 seconds to change from their darkest state to 60 percent clear. The new photochromic lenses meet military specifications for ballistic protection.