Compact Fluorescent Lamps
Compact fluorescent lamps (CFLs) are small-diameter fluorescent lamps folded for compactness. There are several styles of CFLs: two-, four-, and six-tube lamps, as well as circular lamps. Some CFLs have the tubes and ballast permanently connected. Others have separate tubes and ballasts.
Some CFLs feature a round adaptor, allowing them to screw into common electrical sockets and making them ideal replacements for incandescent lamps. They last up to 10 times longer than incandescent lamps, and they use about one-fourth the energy, producing 90% less heat.
However, typical 60-100 watt incandescent lamps are no more than 5.3-inches long, while standard CFLs are longer than 6 inches. Therefore, sub-CFLs have been developed. No more than 4.5 inches long, sub-CFLs fit into most incandescent fixtures.
Because of their energy efficiency, brightness, and low heat output, CFLs are also good replacements for halogen lamps in torchieres.