ABSTRACT
Sodium loss is a long-standing problem of metal halide lamps containing sodium iodide as one of the filling constituents [1,2]. It causes a rise in lamp voltage and this eventually leads to extinguishing of the lamp. Furthermore, due to changes in the salt composition there will be a shift in colour temperature and colour rendering index of the emitted light. Last but not least, the lumen maintenance is affected in a negative way. This contribution consists of two parts. First results will be presented of a study of the effect of sodium loss on the chemistry in the lamp and secondly the mechanism of sodium loss and the role of photoemission will be discussed.
