How to find the hot resistance of an incandescent bulb

[RayRay1132]

How would I measure the resistance of an incandescent bulb while it's lit up?
Thanks in advance, Ray -KD2JID

 

[MaxHeadRoom78]

Measure current and voltage.

 

[Nigel Goodwin]

(and apply ohms law!)

 

[Dick Cappels]

OR...measure the power and the voltage, which might be safer if you have a reliable wattmeter on hand.

 

[unclejed613]

using current and voltage is a more flexible method, for instance measuring the resistance of a forward biased semiconductor junction at a given current, since the junction resistance is nonlinear...

 

[KeepItSimpleStupid]

Just remember,the voltage across and the current through. Remember to not use the same meter. i.e do not meaure current with your DVM and then remove it to measure voltage.

 

[crutschow]

Just remember,the voltage across and the current through. Remember to not use the same meter. i.e do not meaure current with your DVM and then remove it to measure voltage.

The error from doing that should be small.

 

[KeepItSimpleStupid]

Fluke 77. 10A range. 50mV/Amp.

See https://xdevs.com/doc/Fluke/FLUKE 77, 75, 73, 70, 23, 21 Series II Service.pdf

So, 1A at 120V is 120W or a 50mV drop. So, it would probably work. 50mV is tiny part of 120V.
So, the voltage would be off by 0.042% in my case.

 

[RayRay1132]

I'm planning to use a couple of sets of these incandescent bulbs in my homemade high voltage power supply made of a rectified microwave oven transformer. I figure I could install a couple of sockets in series with the primary and secondary's and swap out the bulbs as needed for current limiting.

 

[KeepItSimpleStupid]

A 60W bulb would limit to basically 60W. Usually, you don't want the light on.