neon measurement circuit


Joined Jul 17, 2007
A neon bulb (like an NE-2) generally ionize at somewhere between 55-90v. If you're talking about a neon sign, they can require much higher voltage.

To light an NE-2 bulb using 120VAC requires the use of a current limiting resistor, somewhere between 82k and 330k Ohms - I forget the value offhand. If you don't use a current limiting resistor, you will burn it out almost instantly.

Once the neon ionizes, the voltage across the bulb will drop considerably. You would need some kind of peak detector circuit, or a slowly ramping DC voltage to determine the ionization voltage. The sustaining voltage will be considerably lower, as already mentioned. Once the voltage across the bulb was too low to sustain ionization, it would cease to be lit.


Joined May 16, 2005
Another approach would be to put a current sensing resistor in series with the neon light. When the light is not lit, there will be no voltage across the resistor. When the light is lit, there will be current through the resistor.

Either way, it is a voltage change you are looking for.:)