Photochromic materials are substances that change color in response to light exposure. When exposed to ultraviolet (UV) light, these materials darken, providing protection from harmful rays. Once the light source is removed, they return to their original color. This property is commonly used in photochromic lenses for glasses, allowing them to adapt to changing light conditions. These materials work through a chemical reaction that alters their molecular structure when exposed to light. Photochromic technology is not limited to eyewear; it can also be found in window coatings and smart textiles, enhancing comfort and safety in various applications.