RB- 50 ULTRA LENSES are photochromic and adjust their density (darkness) according to light and temperature conditions. They darken most in cold, bright conditions which make them excellent for winter sports. These lenses also have exceptionally high (99.97%) polarizing efficiency. Throughout their absorption range they block a greater percentage of blue light to improve contrast (80%-95% light absorption). Ultra lenses are fitted only to the Bravura model.