All glow-in-the-dark products contain phosphors. A phosphor is a substance that radiates visible light after being energized. The two places where we most commonly see phosphors are in a TV screen or computer monitor and in fluorescent lights. In a TV screen, an electron beam strikes the phosphor to energize it (see How Television Works for details). In a fluorescent light, ultraviolet light energizes the phosphor. In both cases, what we see is visible light. A color TV screen actually contains thousands of tiny phosphor picture elements that emit three different colors (red, green and blue). In the case of a fluorescent light, there is normally a mixture of phosphors that together create light that looks white to us.