And finally finally! This is a nitrogen spectrum. This tube was deliberately filled with circa 3mmHg of air to demonstrate so called chemical nitrogen afterglow. I believe all of the oxygen was consumed now, so no more afterglow effect, but nitrogen still displays its funny spectrum. At first, one may thought there is some kind of interference on the camera, but no! There is none, and as a sanity check nitrogen spectrum shows the same banded spectrum also on my HP320 spectrometer and even in optical spectroscope. Molecular gases have complex electron interactions resulting in funny wide spectrums. A lot of UV is radiated, too!

About that 589nm line seen in some lamp spectrums. 589nm of course screams Sodium!!! loudly ) So it is easy to understand we can see a marker of ever-present sodium impurity, with it's very intense resonant radiation, likely from oxide coating, as the lamps discussed here are mostly NOS.

Nice experiments, RRK. A few minutes proably won't hurt the tube. Even crap  chinese flyback power supply fixtures for 4, 6, 8 W tubes need several hours for a significant blackening.
If they had neon in the gas filling it would probably be easy to notice like in Nixie tubes and some CCFLs.