When the bulb in a single light fixture flickers, it's seldom a serious problem. You may be using CFL bulbs, which are prone to flickering when they get cold. If your incandescent light bulb is flickering, you may have simply neglected to tighten it. Not all problems that cause flickering are trivial, but if you have a strategy to eliminate all the easy-to-fix possibilities, you'll know when it's time to call an electrician.
Is Another Light Bulb Flickering?
If a single light fixture is flickering, you can be fairly confident that the problem is isolated to that fixture or the switch that controls it. If lights are flickering in other parts of the house, there's a more systemic problem. However, if all the lights flickering are on one circuit, it's easier to isolate the problem than if random lights throughout the house are flickering. All you need to do is an easy test.
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Turn off the breaker that controls the original flickering ceiling light and note if any lights that are still on continue to flicker. If they do, there may be a problem with the power supply coming into the house. Ask the neighbors, and if they don't notice flickering, you need to have an electrician inspect your electrical system. Lights flickering and dimming in a house point to voltage fluctuations that can be caused by loose wiring in the panel, which is a dangerous condition that needs to be fixed.
Lights Flickering on One Circuit
When more than one light on a circuit flickers, it could be caused by an appliance on the circuit cycling on, as noted by Reddi Electric. If not, it points to a loose connection somewhere in the circuit or a faulty breaker. An easy way to tell is to replace the breaker, which will require a modest $20 investment on your part. If the lights continue to flicker, the old breaker wasn't at fault. Save it for a future panel repair or upgrade.
Eliminating the breaker as the cause of the flickering leaves the probability of a loose connection somewhere in the circuit. It could be in a fixture, a switch or somewhere behind the wall. At this point, your best bet is to call an electrician to perform diagnostic tests to find the problem.
Troubleshooting a Flickering Light Fixture
If you're able to verify that the ceiling fixture is the only one flickering, get a ladder and try tightening the light bulb. That may be all you need to do, but if the bulb still flickers, remove it and try another bulb. If the flickering bulb is a CFL, try replacing it with an LED or incandescent bulb. You can also try screwing the original flickering bulb into another fixture to see if it still flickers.
Once you've eliminated the bulb as the cause of the flickering, turn your attention to the switch. If the switch is a dimmer, the problem may be that you're using LED bulbs, which respond to some dimmers by flickering. This is why you might see a ceiling fan LED light flickering. If the switch is a conventional one, remove the cover plate and check the wiring to see if it's loose. If the switch is old and has a loose toggle, replace it.
The last thing you can check is the fixture wiring, and be sure to do this with the breaker off. If you don't find any loose wiring in the fixture, it's time to call an electrician because the loose wiring is elsewhere in the circuit. Loose wiring hidden behind the ceiling or wall is a fire hazard and needs immediate attention.