Gas lighting is the production of artificial light from combustion of a fuel gas such as natural gas, methane, propane, butane, acetylene, ethylene, hydrogen, carbon monoxide, or coal gas. The light is produced either directly by the flame, generally by using special mixes of illuminating gas to increase brightness, or indirectly with other components such as the gas mantle or the limelight, with the gas primarily functioning to heat the mantle or the lime to incandescence.