The effect of hydrogen iodide on the ignition of Hg-free metal-halide lamps

摘要

Trace amounts of moisture (e.g. adsorbed on metal-halide salt pellets during lamp fabrication) may react with the salts during initial lamp light-up to form volatile hydrogen iodide (HI). Hg-free lamps are particularly prone to HI formation since the elemental mercury is not included. The Hg-free lamps can develop high ignition voltages due to the HI, which adversely affects lamp operation especially ignition. This work discusses the thermochemistry and spectroscopic measurements which predict and demonstrate that HI is indeed formed in the reaction of salts and moisture. Experimental confirmation of increased breakdown voltage with increasing concentration of HI (at the ppm level) was obtained in discharge cell experiments. Computer simulations of xenon and HI gas mixtures show qualitative agreement with experiments.