Gas lighting is production of artificial light from combustion of a gaseous fuel, such as hydrogen, methane, carbon monoxide, propane, butane, acetylene, ethylene, coal gas (town gas) or natural 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 as a fuel source. Before electricity became sufficiently widespread and economical to allow for general public use, gas was the most popular method of outdoor and indoor lighting in cities and suburbs. Early gas lights were ignited manually, but many later designs are self-igniting. Gas lighting now is generally used for camping, where the high energy density of a hydrocarbon fuel, combined with the modular nature of canisters (a strong metal container) allows bright and long lasting light to be produced cheaply and without complex equipment. In addition, some urban historical districts retain gas street lighting, and gas lighting is used indoors or outdoors to create or preserve a nostalgic effect.