Carbon Arc Lamp

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Carbon Arc Lamp


a gas-discharge light source in which the radiation of an electrical discharge between carbon electrodes is used. It was developed by P. N. Iablochkin in 1876 for illumination and became widespread in the first half of the 20th century in connection with the development of the construction of searchlights and film projection apparatus.

The carbon arc lamp usually operates on direct current with a series-connected ballast resistance. It consists of two carbon electrodes situated either coaxially or at angles of 40°-130° to each other (the positive electrode is usually mounted horizontally). The lamp is lit by bringing the electrodes into contact, after which they are separated to a certain distance, or by means of an auxiliary electrode. During the operation of the lamp, the electrodes burn and vaporize, and the distance between them is maintained automatically.

Carbon arc lamps are classified as simple (electrodes made of carbonaceous material), flame-type (flammable substances—metal salts—are added to the anode), and high-intensity. In high-intensity lamps, which are the most widespread, the anode is made with a wick that contains mainly salts of rare earths. Such a lamp is distinguished by its high power (more than 100 kilowatts), current (more than 1,000 amperes), brightness (up to 2,000 meganits), and luminous intensity (up to 12 megawatts-steradians-1 - m-2). Carbon arc lamps are used in searchlights and film projection equipment and in powerful radiation equipment such as optical furnaces. The further improvement of carbon arc lamps is proceeding in the direction of improving the current density on the anode and the uninterrupted service life of the lamp and the provision of greater convenience in operation. Carbon arc lamps that operate in an inert atmosphere, as well as lamps stabilized by a vortex current of gas, are being developed.


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