Infrared continuum radiation from metal halide high intensity discharge lamps

Abstract

Infrared (IR) continuum radiation from the arc of a metal halide high intensity discharge lamp was measured and modelled. There are three contributions to the near IR continuum from free electrons: electron–Hg atom bremsstrahlung, electron–ion bremsstrahlung and electron–ion recombination radiation. Electron–Hg atom bremsstrahlung is the most important of these. The radiation transport model utilized empirical Hg density, arc temperature and electron density maps. The line width of the Hg 71S0 to 61P1 resonance broadened transition was used to determine the arc core Hg density. The arc temperature as a function of radius was determined using the radiance of the Hg 9860, 7311 and 7166 cm−1 lines. Relative densities of neutral Dy atoms and Dy ions as a function of radius were found using an Abel inversion of the relative line radiance of selected Dy I and Dy II lines. A Saha analysis was used to determine the electron density in the lamp. The continuum is 73% of the total near IR radiation in the 4000–12 800 cm−1 range.