Photochromic sunglasses react automatically to the available sunlight. On overcast days the lens tints are medium to light. On sunny days they darken to a comfortable sunglass tint and when you go inside, they lighten up. Since they darken and lighten in response to the amount of sunlight you can wear them from dawn to dusk and never have to take them off. These safety sunglasses from Global Vision are made to high quality specifications in order to meet the requirements of the European CE EN-166-F and American ANSI Z87.1 standards. They must pass six different tests for optical quality plus three different tests for impact resistance including a test that shoots a 1/4 inch steel ball at over 100 mph and leaves no more than a dimple on the lens.
Please note, photochromic lenses react to UV rays and do not darken when worn behind a helmet visor or motor vehicle windscreen that filters out UV light.