An incandescent lamp is an electric light with a wire filament that is heated until it glows. The filament is placed in a glass bulb with a vacuum or inert gas to protect the filament from oxidation. The current reaches the filament through terminals or wires embedded in the glass. Historians Robert Friedel and Paul Israel name the inventors of incandescent lamps before others, Joseph Swan and Thomas Edison. A halogen lamp is an incandescent lamp with a small amount of halogen gas, usually iodine or bromine, as the atmosphere in a quartz or aluminosilicate glass lamp. In ordinary incandescent lamps, tungsten evaporates under the influence of heat and deposits on the inner surface of the glass lamp and darkens its surface. The main characteristic of the halogen lamp is the connection of tungsten and halogen gas in the glass lamp, which is called the halogen cycle. The first lamp to use halogen (chlorine) gas was patented in 1882, but the first commercial halogen lamp to use iodine as the halogen gas was patented in 1959 by General Electric. This lamp was developed by Elmer Fridrich and Emmet Wiley who worked at General Electric in 1955. Since 1980, the halogen lamp has been improved and developed.