The term fluorescence also refers to the light emitted by these substances. Many gases, liquids, and solids become fluorescent when exposed to radiation or to electrically charged particles. Fluorescent lighting is widely used in factories, offices, and schools and in some homes. Many highway lights contain fluorescent mercury vapor. TV picture tubes and electron microscopes have fluorescent screens.
Biologists stain cells and tissues with fluorescent dyes to observe biological processes.
Chemists detect certain air and water pollutants by using fluorescence. It also is used to detect lead poisoning and to identify minerals. The color of fluorescing light depends on the substance involved and on the type of energy absorbed. In most cases, the wavelengths of fluorescing light are longer than those of the absorbed radiation. Many kinds of energy cause fluorescence.