Arc light is any lighting device in which an electric current produces light by leaping across a gap in a circuit. The two ends of the gap in the circuit are called poles or electrodes. The current flowing between the electrodes produces an electric arc (see Electric arc ). The arc causes the ends of the electrodes to become extremely hot, and the heat results in intense brightness.
The electrodes of a typical arc light are two pointed rods, generally made of pure carbon or of carbon mixed with various chemicals. The current leaping from the end of one electrode to the nearby end of the other causes them to turn to glowing vapor and gradually waste away. For this reason, an automatic electrode feeding mechanism is necessary to keep the ends of the electrodes the proper distance apart. A regulating device keeps the current flowing at a uniform rate.
The carbon arc lamp was the first practical commercial electric lighting device. Arc lights are now used chiefly where extremely bright and concentrated light is needed. For example, the carbon arc lamp is used in searchlights, theater spotlights, photography, therapeutics (treatment of diseases), microscopes, and special lighting research. The high-pressure xenon short arc provides an excellent light source for motion-picture projectors.
See also Electric light .
