I have recently discovered a small box device that used to have an indicator bulb on it that would switch on when a switch was flicked. I am not sure what voltage to give the bulb, or if its AC or DC, though I assume it is AC because it says 125VAC. This is a picture of the bulb: Bulb

I am not experienced with circuits at all and I know very little about voltage, amps, resistors, and power supply. What would I need to make this work? Can I use a household battery?


1 Answer 1


That looks like a common neon pilot lamp assembly. It should work when directly connected to 120 V AC (common household power in the US and Canada).

I've also seen these assemblies using an LED as the light source - but still designed to be connected directly to 120 VAC.

  • \$\begingroup\$ But why does it say 125 then and not 120? \$\endgroup\$
    – ACD
    Commented Jun 23, 2015 at 20:37
  • 1
    \$\begingroup\$ @ACD Because household voltage can vary slightly. In the United States and Canada, national standards specify that the nominal voltage at the source should be 120V and allow a range of 114V to 126V (±5%). Lamps, switches, receptacles, relay contacts etc. are typically spec'ed at 125VAC. \$\endgroup\$
    – tcrosley
    Commented Jun 23, 2015 at 21:54

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