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# Light bulbs

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There are several ways to calculate light bulbs. Producing a 60W light bulb at 120Vac is one way. Measuring the resistance of the filament and the applied voltage is another way. But, the best way of all, is to determine the combined resistance and reactance, then apply the voltage and then determine resistance.

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What's the purpose of this thread? Are you asking a question or making a statement?

An incandescent light bulb is nearly purely resistive and has virtually no reactance so will have a power factor near 1.

The resistance of the filament varies with temperature which is also dependant on the current so the current drawn by the bulb when it's on can't be deturmined by measuring its cold resistance and applying Ohm's law.

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Hi KelvinIV,

there is one known and reliable method to calculate for filament resistance for me:

Measure the current flow with the lamp being supplied by its nominal voltage.

Then use Ohm's law to determine the resistance.

Filament type lamps have very low cold resistance which increases with heating.

HtG

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To show you what to expect using Herman's advice, here are a couple of graphs I picked up in the net sometime ago.  Sorry I can't credit the author.

Ken

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Thanks, I assume that those graphs can be scaled for different bulbs, with other power ratings.

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It looks like it was for a 100W bulb. It was just a general example of how someone used voltage and current measurements to determine the filament's resistance over a range of operating voltages.  And how the graphed data would look...if the OP tried it.

ken

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