carbon-arc

Archaic method of creating an intense source of light. In our industry, at one time was common in followspots and movie projectors. Has been replaced almost, but not completely, by the Xenon lamp light source. Older venues still have and use carbon-arc spots and even more 35mm film projectors. In most, an arc is formed by passing current through two pencil-sized, copper-jacketed, electrodes, about 3/8" apart. As the electrons jump from the negative cathode to the positive anode, visible light (as well as a great amount of UV radiation) is produced. Carbon arc is one of many subsets of discharge (arc) sources.
See also incandescense, "gaseous discharge," and fluorescense.