> Neon bulbs can lead to a lot of electronics study in a small package.
> The "battery" must be above the firing point of the neon bulb. 135 volt
> battery usually
good, but a higher voltage than is really needed
, or 150 volt powersupply. The polarity doesn't matter.
> Neon bulbs fire from 105 to 130 volts IF get hit by light or particles
> from outer space. Many newer bulbs have small (very) amount of
> radioactivity inside to stabilize the firing point.
Gas-discharge devices such as T/R tubes used in radars all include a
radioactive "primer" so they will ignite consistently in the dark.
The light sensitivity effect is readily observable, particularly in a
bulb which has been run a lot and has significant bulb darkening. I
used to demonstrate this with an old Tektronix 535 scope, which had the
horizontal sweep voltage (150 volts max???) brought out to a front
panel binding post. With a protective resistor between the sweep
voltage and a bult with one ended grounded the breakdown point was
observable simply by hooking one of the Y-axis channel inputs to the
"top" of the bulb. Even small amounts of light will affect the firing
(striking) voltage enough to change the position on the horizontal trace
where the bulb fires. By the way, when I was making measurements of a
neon-bulb relaxation oscillator before making that posting the other
day, I could see the influence of the light from the fluorescent fixture
above my work bench; when the light was present the oscillation
frequency was higher and the blinking somewhat irregular due to the
accidental timing between the light and the time when the voltage rose
to the firing point. Easy experiment to run, even without a scope!