Comparison of high-pressure discharges in mercury and the halides of aluminium, tin and lead

Abstract

In a search for an efficient metal halide lamp with a continuous spectrum and only one metallic constituent other than mercury, the spectra, luminous efficacies and colour rendering indices of discharges containing the halides of aluminium, tin and lead have been investigated. The luminous efficacies have maxima which depend on the dosing densities of mercury and metal halide. The highest observed luminous efficacies at 400-500 W were about 109 lm/W for AlCl3, 90 lm/W for SnCl2 and 90 lm/W for PbCl 2. Low colour temperatures are obtained at the expense of luminous efficacy and constancy of colour. Arc stability, electrode erosion and reactions with the silica arc tube present problems in making a practical lamp. An alkali halide additive improves the discharges and can provide a high luminous efficacy at a relatively low colour temperature.