How to Test a Light Fixture With a Voltmeter

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Things You'll Need

  • Tools, as required to remove any covers and the fixture itself

  • Safety goggles

Warning

Be careful not to touch exposed wires, as electrical shock could be fatal or could cause you to fall off the ladder. Never work alone. Have someone nearby in case of an accident. Do not let “hot” wires touch together. Sparks and flying molten metal can cause severe burns, especially to the eyes. Wear safety goggles.

Any light fixture can be tested with a voltmeter, whether it uses a bulb, a fluorescent tube or any other type of lighting source. However, because of the risk of electrical shock, this should only be done by a person with experience using a voltmeter. This is not a task for a first-time user, nor is it a way to learn how to use a voltmeter. And because there are so many different types of light fixtures, you should be able to remove any covers and remove the lighting element without detailed instructions, or by consulting the installation instructions that came with it.

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Check Voltage at the Contacts

Step 1

Shut off the circuit breaker that feeds the lighting fixture.

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Step 2

Remove any covers and remove the lighting element.

Step 3

Turn on the circuit breaker and the switch that feeds the fixture.

Step 4

Set up the voltmeter to read at least 240 volts.

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Step 5

Touch the voltmeter leads to the contacts that directly touch the lighting element. If you read 120 volts, the fixture is good. If not, the fixture could still be good, but you could have other problems. You will need to go to the next section to find out.

Check the Input Voltage

Step 1

Shut off the circuit breaker that feeds the lighting fixture.

Step 2

Disassemble or remove the light fixture to find the wiring coming into it.

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Step 3

Find a place on the input wiring to connect the voltmeter. You may need to open a junction box, remove wire nuts or disconnect terminals, depending on the fixture. Make sure no exposed wires are touching each other or anything else.

Step 4

Turn the breaker and switch back on.

Step 5

Touch the voltmeter to the input wires or connections. If you read 120 volts, the light fixture is good. If not, you could have a bad breaker, bad wiring or a bad switch. You must fix the problem to a point where you have 120 volts at the input to the fixture.

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Step 6

Repeat the first section to retest the light fixture. If you have voltage at the lighting element contacts, the fixture is good. If you don't, and you know that the input voltage to the fixture is good, then you have a bad light fixture.

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Richard Asmus

Richard Asmus was a writer and producer of television commercials in Phoenix, Arizona, and now is retired in Peru. After founding a small telecommunications engineering corporation and visiting 37 countries, Asmus studied broadcasting at Arizona State University and earned his Master of Fine Arts at Brooklyn College in New York.