Light-sensitive chemicals, also known as photosensitive compounds, are substances that change their properties when exposed to light. These chemicals are commonly used in various applications, including photography, where they help capture images on film, and in solar cells, where they convert sunlight into electricity. When light hits these chemicals, it can trigger a chemical reaction or change their structure, leading to different physical or chemical properties. This characteristic is essential in fields like photolithography, used in semiconductor manufacturing, and in photochromic lenses, which darken in sunlight to protect the eyes.