A theoretical analysis of the behavior of 400-watt Hg + TlI arc lamps with variable mercury loadings is performed. It is quantitatively shown that, as the Hg loading is doubled, the following effects may be predicted: (a) the effective arc temperature decreases from 5100 K to 4800 K, (b) the effective radius increases by ~10%, (c) the escape factor for the imprisoned Tl 5350 Å line increases ~40%, (d) the power radiated in the Tl 5350 Å line increases ~10%, and (e) the power radiated in the Hg visible line decreases ~15%. These results are in agreement with the experimental observations of Larson. These effects result in an increase in the lumen-per-watt ratings, which is of technological significance. Self-absorption is an important factor in the radiation of the Tl 5350 Å line, and it is shown that the experimental observations are reasonably consistent with the assumption of local thermodynamic equilibrium.
C. F. Gallo, "Theoretical Analysis of the Behavior of Mercury plus Thallium Iodide Arc Lamps with Variable Mercury Loadings," Appl. Opt. 9, 2711-2716 (1970)