Photochromic pigments are special materials that change color when exposed to different light conditions. They typically become darker when exposed to ultraviolet (UV) light, such as sunlight, and return to their original color in the absence of UV light. This property makes them useful in various applications, including sunglasses and photochromic lenses. These pigments work by undergoing a chemical reaction that alters their molecular structure in response to light. When the light intensity decreases, the pigments revert to their original state. This unique feature allows for dynamic color changes, enhancing both functionality and aesthetics in products like clothing and coatings.