Photochromic pigments are special materials that change color when exposed to ultraviolet (UV) light. These pigments can be found in various products, such as sunglasses and photochromic lenses, which darken in sunlight and return to their original color indoors. This property helps protect the eyes from harmful UV rays. The mechanism behind photochromic pigments involves a chemical reaction that alters the structure of the pigment molecules. When UV light hits these pigments, they absorb the energy and undergo a transformation, leading to a change in color. This reversible process makes them useful in everyday applications, enhancing both functionality and style.