Smith Polarchromic lenses combine the glare-free benefits of advanced polarization with UV-sensitive, self-tint-adjusting photochromic technology. Precise amounts of silver halide crystals are infused into the glass lens material during their creation. These microscopic crystals automatically change orientation in response to UV light which results in a shift in tint, either increasing or decreasing Visible Light Transmission (VLT) and fine tuning the tint of your lens in response to changing ambient light conditions throughout the day. Smith's Polarchromic technology never wears out or gets tired, lasting the life of your sunglasses. The result? You get a lens which offers crisp optics and soothing light levels at all hours, allowing you to focus on what matters most from dawn to dusk.