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Description

Fluorescent paint, or black light paint, glows in ultraviolet light. This is an example of photoluminescence. Phosphorescent paints also emit light when excited by visible or ultraviolet light, but do so over extended periods. This long-lasting effect of phosphorescents also allows kids to enjoy “glow-in-the-dark” adhesive stars on the ceilings of their rooms.

Common phosphorescents include petroleum jelly, glow-in-the-dark paints, the quinine in tonic water, and some detergents. Clocks and watches have their faces or numbers and hands coated with phosphorescent paints so that we can see the time in the dark. Emergency routes, doors, and stairways are often marked with theses paints so we can find our way out of buildings when the power fails.

One of the most familiar applications is the fluorescent light bulb. When the light bulb is turned on, an electrical current passes through mercury vapor in the light bulb. The current excites the mercury atoms. As electrons in the mercury atoms drop back from their excited state to their ground state, they emit photons of ultraviolet light. The inner surface of the glass tube is coated with a fluorescent chemical, which emits light when excited by this ultraviolet light. These tubes are more efficient and longer lasting than incandescent bulbs.