Meter testing an incandescent bulb

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Eddy Current

Senior Member
Other than the old shake or look inside at the filament, is there any way to check an incandescent bulb with a meter? I was just curious.
 

kwired

Electron manager
Location
NE Nebraska
For incandescent, simple continuity check is normally all that is needed. No continuity means no circuit through the lamp, which means no current will flow when voltage is applied.

For lamps that illuminate via current flowing through a gas, like fluorescents or HID's this test doesn't mean much.
 

kwired

Electron manager
Location
NE Nebraska
I do not think so, I also know only one that traditional way of checking an incandescent bulb. Is there any one else with some other technique?

What do you disagree with? An incandescent lamp is a resistive load, in an inert gas so the filament doesn't burn up. If you have continuity through the filament it is going to light up if minimum voltage necessary to make it light is applied, now if the inert gas has leaked out it will not light for very long before the filament burns out because if oxygen gets in there it will burn out pretty fast at the temperature it operates at. If you have no continuity you will have no current flow through the filament and it will not heat up to produce any light regardless of any other conditions.

You can not easily tell how many watts a lamp is by measuring its resistance because it changes when the filament temperature increases during operation, but you can get a fairly basic go / no go test that is fairly useful most of the time by simply checking for continuity.

I guess the other easy technique is apply rated voltage and if it lights it is good:roll:
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I do not think so, I also know only one that traditional way of checking an incandescent bulb. Is there any one else with some other technique?
Sure, continuity check with a meter, as kwired said. Shake doesn't work if the filament is only severed at one end, and look is hard with a frosted bulb. Neither method works for CFL or LED, though. The obvious and easiest way which works for all lamp types is to unscrew a working lamp and replace it with the questionable one, and see if it lights up.
 
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dhalleron

Senior Member
Location
Louisville, KY
Umm. I just screw the bulb into a known good socket.

I have been under a house or in an attic with my drop light and bumped it hard enough to burn it out. Since I never crawled with spare bulbs I found I could sometimes shake the bulb and the filament will weld back together.

In that case a continuity test might show the bulb is good, but the broken filament was usually shorter and will burn out again sooner.
 
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