ABSTRACT
INTRODUCTION Modern high-pressure metal halide lamps contain a mixture of molten salts consisting of metal halides that partially vaporise under operating conditions. Typical constituents of the melt are alkali halides AX (A = Na, Cs; X = Br, I), rare earth metal halides LnX3 (Ln = Dy, Ho, Tm; X = Br, I) as well as indium or thallium halides. The cations from the gaseous metal halides strongly contribute to the radiation of a lamp and determine its lighting properties [1]. The system investigated here consists of three different line radiators, namely sodium, thallium and indium. Their contribution to the light is yellow-orange, green and blue, respectively. The light intensity and colour rendition depends on the concentration of the different radiating metals in the arc column, which in turn is related to the partial pressures of the metal-containing species above the melt.
