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  • How to test a light bulb

    Follow the steps below to test a incandescent, fluorescent, or LED bulb.

    Test Light Bulb

    Step 1- Set up the multimeter.

    Set the multimeter to the resistance Ohms position.

    Step 2- Test resistance across the bulb filament.

    Place the red meter probe on the very tip of the bulb, and the black probe on the side (ground metal).

    Step 3- Review the results.

    The measurement should read some amount of resistance through the bulb filament. A common incandescent light bulb has approximately 18 Ohms, but this amount could vary among different size, brightness, and brands.




    Fluorescent Bulb Test

    Step 1- Set up the multimeter.

    Set the multimeter to the resistance Ohms position.

    Step 2- Test resistance through the electrodes.

    Place a meter lead on the two end piece metal contacts, and you should read continuity, or zero Ohms. Note: Each meter probe goes on the contacts next to each other on one end, and then test the opposite side.

    Note: Sometimes you can get a false reading though if the inner workings of the electrode become shorted together. If the contacts on both side are reading correctly, but you still suspect the bulb faulty, try this:

    Alternate Fluorescent Bulb Test

    Find a known good fixture to try the suspected bulb in. If the bulb works, then it was most likely the ballast or starter that was not working properly. Note: Most fluorescent bulbs work as a pair and depend on the other to work, so move both bulbs to a working fixture together to test them.


    LED Bulb Test

    Step 1- Set up the multimeter.

    Select the diode setting on you multimeter. The diode setting is commonly found in the resistance range of the multimeter.

    Step 2- Test resistance across the LED leads.

    Measure resistance across the LED leads, then switch the meter probes to the opposite lead it was on before. One reading should show an open or no continuity and the other reading should display some amount of resistance.

    Step 3- Review the test results.

    If you read zero Ohms both tests in step 3, then the LED is shorted. If you read an open both tests, the LED is electrically open.

    Click here to watch the LED test video.

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