Continuum radiation in a high pressure argon–mercury lamp

Abstract

In typical high pressure high intensity discharge lamps about 60% of the deposited power is released in non-useful channels, non-radiative heat transfer from the hot arc core, ultraviolet radiation and infrared radiation, of which the last is the dominant one.To reduce the amount of infrared radiation emitted in high pressure argon–mercury lamps the sources of continuum radiation are identified, quantified and compared with results from emission spectroscopy. Objective data, especially for mercury, are lacking, which makes experimental verification necessary.Three possible continuum radiation sources were examined: electron–atom free–free bremsstrahlung, electron–ion free–free bremsstrahlung and electron–atom free–bound recombination radiation. The radiance caused by each of these processes can be calculated from test lamp fillings and the temperature profile in the lamp using a computer program. From comparing experimental results with computer calculations, the electron–mercury atom bremsstrahlung process has been determined as dominating the infrared radiation.