LTE AND NEAR-LTE LIGHTING PLASMAS

High-pressure mercury lamps, metal halide arc lamps, high-pressure sodium lamps, xenon short-arc lamps, xenon flashlamps, and microwave-excited metal halide lamps are extremely important commercial applications of LTE and near-LTE plasma physics. In the first three of these the objective is to achieve discharges in which radiation is the dominant mode of power dissipation, while at the same time minimizing the power radiated as continuous-spectrum emission from electron-electron, electron-ion, and electron-neutral collisions. Meeting this objective permits an efficiency of the conversion of electrical power to light as great as 33%. The factors controlling the power balance and the luminous efficacy of such sources are discussed. Current research in modeling these complex plasma devices is described. This has reached the stage that successful CAD models are available for new-product design in mercury and high-pressure sodium lamps, but not yet for metal halide lamps. The behavior of electrodes is discussed as an important practical determinant of lamp life. Directions of future research and development are briefly discussed.