The open-air concentrated-arc lamp is a new form of the concentrated arc which operates in the open air and does not require any enclosing bulb or protective atmosphere. The light source is a sharply defined, circular spot which is formed on the end of the electrode by a thin film of incandescent molten zirconium. The lamps can be operated from alternating or direct current and can be made in sizes up to several kilowatts. A 1-kw lamp operating on alternating current draws 18 amp at 55 v and produces 3000 candlepower from a spot 5.4 mm in diameter whose average brightness is 130 c/sq mm. The radiation has a continuous black-body type of spectral distribution and a constant color temperature of 3600 K. Due to a unique operating principle whereby the zirconium metal is constantly renewed from its own products of combustion, the lamps can have lives of several hundred hours. The exhaust products are nontoxic and the electrodes are replaceable. The lamp is characterized by extreme stability and ease of operation. It is expected to find application in projection, television, flood and spot lighting and other fields which require intense light sources.