Serengeti Vasio Sunglasses (Dark Tortoise Drivers Polarized) Photochromic technology designed to constantly adjust to changing light conditions Spectral Control technology gives you stunning, high-definition contrast and color enhancement Polarization technology engineered to eliminate distracting glare Using only the highest quality injected nylon for superior durability, exceptionally light, flexible and comfortable All Serengeti lenses offer the latest in photochromic technology, which constantly lightens and darkens throughout the day to ensure you see every detail.