SODIUM-VAPOUR LAMP

electric discharge lamp using ionized sodium, used for street lighting and other illumination. A low-pressure sodium-vapour lamp consists of a glass shell with metal electrodes, filled with neon gas and a little sodium. When current passes between the electrodes, it ionizes the neon, giving a red glow, until the hot gas vaporizes the sodium. This ionizes and shines a nearly monochrome yellow. High-pressure sodium-vapour lamps, made with a mixture of mercury and sodium, give a whiter light and are used for extra-bright lighting in places such as road intersections and sports stadiums.