Light Bulb continuity
Light Bulb continuity
(OP)
Dumb old structural here with an $8.00 Radio Shack tester.
I would have thought that a light bulb (known to work) would show continuity - but it doesn't. IS the resistance too high??
Or do I just not know what I am doing?? Has happened before.
I would have thought that a light bulb (known to work) would show continuity - but it doesn't. IS the resistance too high??
Or do I just not know what I am doing?? Has happened before.





RE: Light Bulb continuity
The resistance of a cold light bulb is much less than you'd calculate by R=P/V^2 (where P = watt rating and V =voltage) as a result of temperature coefficient of resistance.
I don't know what the cutoff is for your tester, but I'd have thought you'd see an open.
Does your tester allow you to check resistance?
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(2B)+(2B)' ?
RE: Light Bulb continuity
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Light Bulb continuity
RE: Light Bulb continuity
A typical continuity tester might reject anything even close to 10 ohms: http:
Obviously, there are others where 2K is acceptable: htt
And others that are in-between at 400 ohms: http:/
One Radio Shack instrument buzzes at less than 50 ohms: http://sup
I don't know what kind of tester you have, but presumably, you're just using the continuity position of the ohmmeter function, in which case, you should just measure the resistance directly.
TTFN
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RE: Light Bulb continuity
Just trying to find a fault in a circuit.
THANKS for your help!!
RE: Light Bulb continuity
Describe the light bulb in more detail. Is it household, or is it a small flashlight sized bulb.
Why are you testing a light bulb if it's known to be good?
RE: Light Bulb continuity
RE: Light Bulb continuity
It must be a resistance thing. Again - THANKS!
RE: Light Bulb continuity
40 watts at 120 volts gives R = 360 ohms
Typical tungsten filaments will undergo a 10:1 to 12:1 increase in resistance from cold (unlit) to hot (lit), so a typical cold/unlit resistance might be 30 to 40 ohms.
RE: Light Bulb continuity
Since we (and you) know nothing about the "tester" and its performance specifications, discussing it further seems rather futile.
TTFN
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RE: Light Bulb continuity
AGREED - just thought a light bulb would show continuity - NOW I KNOW better. Obviously a resistance thing. Now I can go out and try not to kill myself and come back with some other dumb questions.
RE: Light Bulb continuity
TTFN
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