A type of electric-discharge lamp in which an electric current flows between electrodes through a gas or vapor. In most arc lamps the light results from the luminescence of the gas; however, in the carbon arc lamp a major portion of the light is produced by the incandescence of one or both electrodes. The color of the arc depends upon the electrode material and the surrounding atmosphere. Most lamps have a negative resistance characteristic so that the resistance decreases after the arc has been struck. Therefore some form of current-limiting device is required in the electric circuit. For other electric-discharge lamps