The addition of metallic iodides to mercury arc lamps has proven to be an effective and practical method of altering the spectral output. If the excitation levels of the metal of the dissociated iodide are lower than the excitation levels of mercury, the mercury arc temperature is considerably reduced. Experimental evidence for this phenomenon is presented.
C. F. Gallo, "The Effect of Thallium Iodide on the Arc Temperature of Hg Discharges," Appl. Opt. 6, 1563-1565 (1967)