Construction Heavy Equipment

It has to do with two things: polarity and capacitance. The small machine’s top terminal is small but sufficient to gather enough charge so that, at the lesser voltage of its discharge, the air is brightly ionized. Sparking to a matched sphere also helps. Here it’s hitting a smaller sphere at maximum gap, so dimmer. This one sparks quite brightly to a matched terminal.
I have completed the opposite polarity partner to this machine, so “Joachim” and “Boaz” will be putting on a show shortly.