The Nias photochomic polarized lenses darken depending on the amount of sunlight. There is a 40% difference which takes the lens from Category 2 to Category 3 protection. The lens darkens in intense sunlight and lightens in low light conditions. Photochromic lenses are ideal for sailing and boating in all weather conditions. The Nias acetate polarized photochromic model is offered in a Black frame and is available with Grey or Amber lenses. Supplied with a soft neoprene case, cleaning cloth and leash.