Fluoresecent tubes only work intermittantly

[felix]

Good point supersparks. You do get variations in brightness depending on what you're standing on and, more importantly, whether or not you have your finger on the back end of the driver.

A lot depends on what garyeuph meant by "barely lights up". Since this is subjective the test is not 100% reliable. I stand corrected.

 

[ban-all-sheds]

I'm no expert in the use of magic screwdrivers, but doesn't a neon either strike or not?

 

[felix]

A neon will strike at about 70 volts peak. That's 50 volts rms. The brightness depends on the current that flows afterwards and this depends on both the voltage and the total impedance in the circuit.

The driver itself will typically have a 100 kilohm resistor in it. The external circuit contains many parts, one of which is the tester's body. Some of these parts are capacitors like the one formed between your hand and the screwdriver's innards. You can bypass this one by putting your finger on the back end of the driver. The next capacitor in the line is between your body and earth. You can bypass this one as well by touching earth with your other hand but, as they say on TV, don't try this at home!

When a screwdriver barely lights up it probably means that either (a) the voltage is too low or (b) there is another capacitor in the circuit such as that between two adjacent cable cores or (c) both.

 

[supersparks]

i hate neons