I found this picture describing types of discharges in a tube:
https://www.researchgate.net/figure/A-schematic-of-the-dc-glow-discharge-showing-the-several-distinct-regions-that-appear_fig3_320454510
This is all fine and dandy, but I have questions:
1) Color Differences:
From what I have seen, the color of a positive-column discharge is usually different than the negative-glow discharge, even when the same filler is used. Why is this?
2) Presence of different glows:
In a neon indicator, there never seems to be any anode glow at all. What makes these certain glows appear in some discharges but not all?
Thanks!
(1) Electrons speed/enegry/'temperature' whatever you like to call it, is higher at the area near the cathode. So different energy levels of the gas atoms external electron orbits can be excited on interaction. More so, for some gas mixes like Ne/Hg or Ne/Kr or Ne/Xe, Ne glow is excited only around the cathode, with Hg/Kr/Xe dominating the column. See this at plasma globes or at Philps TUV6 glow discharge UV lamp pictured here. To
@dor123 - plasma globes sure a run on AC, yet stil this phenomena is observed!
(2) Just no space for a discharge column. Try to excite a nixie lamp in a non-prescribed way - reverse polarity, non-functional pins or so - you'll see the column, in a gorgeous blue mercury glow for many nixies! Anode glow as a thin film around the *anode* seems not to appear in the most common types of glow discharge we see.
