Dead sodium lamp in series with a mercury lamp from a multiplier with 4kV output

Electric pulses were passed through this sodium lamp for long periods of time and eventually it stopped glowing. But in this case we see that at first it passed current and did not glow, and later on a strange discharge appeared in it. In the past, it has changed its glow color after exposure to pulses in these tests: The mercury lamp was taken from a normally used luminescent lighting lamp. It was much less exposed to the pulses. Another similar lamp, with a long history of exposure to pulses, was covered inside with a dark shiny substance, and also had some powder of an unknown substance inside, and yet it continued to operate at elevated voltage.