A light source consisting of a long glass tube containing mercury in a partial vacuum. Available in many lengths and several diameters, the tube is lined with a fluorescent phosphor. When the mercury is excited by electricity, it emits ultraviolet (UV) light, which causes the phosphor to emit visible light. Fluorescent lamps have been widely used in commercial buildings for decades, because they use considerably less power and last much longer than incandescent lighting. However, due to their tubular design and cooler color temperatures, they have not been generally welcome in the home. The Compact Fluorescent Lamp (CFL) Compact fluorescents are designed to replace the standard incandescent bulb and screw into everyday table lamps and lighting fixtures. They are available in soft, warm hues like incandescent bulbs. See fluorescence, incandescent bulb, halogen bulb, LED bulb and color temperature.