Serengeti Rotolare Sunglasses (Dark Tortoise Polar PhD Drivers) 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 Polar PhD lenses superior eyewear for the ultimate journey, the latest in polarization, photochromic technologies, exclusive hues and high-definition benefits that are near-glass in clarity All Serengeti lenses offer the latest in photochromic technology, which constantly lightens and darkens throughout the day to ensure you see every detail.