This is a film scan of the only old metal halde lamp I have been able to find with an Indium-Thallium-Mercury-Sodium formulation. This lamp, most likely 400watts, was paired up inside ground mounted fixtures illuminating a sign on both sides.
I had such confusion about the spectral line positions when I shot this nearly 25years ago, I actually had to measure them. Almost looked like MV spectra at a glance, but not exactly. Luckily the very familiar Mercury (Hg) and Sodium (Na) lines were distinct. I found the 535nm line which was almost certainly from Thallium (Tl) and the lines from Indium (In) I identified after visiting a local library; found a description of a formulation of a metal-halide lamp under a section on lighting history in an encyclopedia.
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