Photochromic compounds are substances that change color when exposed to light. This property allows them to absorb and reflect different wavelengths of light, resulting in a visible change. Common examples include certain types of sunglasses that darken in sunlight and return to their original state in the dark. These compounds are often used in various applications, such as optical lenses, smart windows, and sensors. The ability to switch between states makes them useful for enhancing comfort and protecting against harmful UV rays. Researchers continue to explore new photochromic materials for innovative uses in technology and design.