arc lamp

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An electric light in which a current traverses a gas between two incandescent electrodes and generates an arc that produces light.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An electric arc arranged so as to produce useful light.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a lamp that produces light when electric current flows across the gap between two electrodes