These are super cool, never seen a clear bander one before! Does yours not have a mercury-blue color stage during warmup (after neon red but before sodium yellow)? I really wish they made unsaturated versions of penning-start HPS lamps for use with CWA ballasts.

That's an unusual type indeed! The clear variant seems to have been way more commonly used in North America, which is interesting given that fluorescent coated mercury lamps where already very common during the 1970s, which makes you wonder if photometry was a consideration at all when mercury luminaires were retrofitted with such (clear) sodium lamps.

@Drew - This lamp didn't go blue at all in the warm-up sequence as seen on the right, which surprised me.
@Max - Yep, the clear version was way more common. Most luminaires over here worth their value were designed around clear lamps for distribution control. I think that coated lamps were only used for their color corrective properties, which partially defeated the intended distribution, and produced wide blobs of light. Using coated lamps in a NEMA-head did make an improvement in performance by creating more usable light without defeating the optics, especially if they were Type V.