These lenses are dark outdoors in the daylight and lighten automatically to almost clear when worn indoors or at night. Lenses require UV exposure to initiate the change in color and shading. Photochromic lenses usually need a few exposures to reach their full potential. Note: All photochromic lenses will not darken behind a faceshield or windshield that blocks UV light and will not fully darken in extreme heat. They're great during normal weather conditions of warmth and heat or during cool downs.