ABSTRACT
Quartz metal halide lamps are commonly produced using Th02-doped tungsten (thoriated) electrodes. ThO, reduces the work function of the electrodes. As a result, the glow-to-arc transition period is reduced and the extent of tungsten sputtering and collection of dark deposits on the quartz wall can be reduced. However, in lamps made with Nal-Sci3 doses and thoriated electrodes, a continuous increase in ThI4 content in the salt is observed as the lamps are burned [1]. It is thought that Th07 from the electrodes forms excess ThI4 in these lamps. In the present study, lamps were made using both thoriated and pure tungsten (nonthoriated) electrodes and the salt composition was analyzed at various stages of life to better understand the Th14 increase in lamps and its effect on lamp operating conditions. Several alternate dopants such as La203, Ce02, ZrO, and Y203 have also been studied to determine if they are substitutes for ThO, [2]. It was thought that by adding ThI4 to the salt dose, one may be able to use dopant-free electrodes without adversely affecting the lamp performance.
