Neon bulbs are curious critters. As you say, they have hysteresis -- a
higher strike voltage than sustaining voltage. The company I worked for
once used them as low current regulators here and there, as well as for
static protection, so they bought or selected them to various
specifications for strike and sustaining voltages. Strike voltages
varied from 55 minimum to 135 maximum, and sustaining specs went from a
minimum of 46 to a maximum of 78. They also exhibited a "dark effect",
which I believe was that the strike voltage was dependent on the ambient
light level. I recall that a trace radioactive material was added to
some -- to reduce the "dark effect", I think, by keeping the gas close
to ionization. I imagine the sustaining voltage was controlled by the
mixture and pressure of gas.

The bulbs were commonly used as pilot lamps, but not when the supply was
DC. (This lesson was learned the hard way, judging by company documents
and app notes.) Depending on the supply impedance, the pilot bulb could
become a relaxation oscillator, interfering with sensitive circuitry.

I came in just as their day was ending.

Roy Lewallen, W7EL

Avery Fineman wrote:

Allow me to correct a number. The strike voltage of a typical small
neon bulb is high but once struck, and a resistor is in series with it,
the bulb potential is around 50 VDC.
. . .