The short answer
Lights flicker when the voltage reaching them is not steady. That can happen at four different levels, and which one you are in determines whether this is a ten-minute fix or a same-day call. At the BULB OR FIXTURE level it is usually an LED and a dimmer that were not built for each other, which is the most common cause we see and is not a fault in your wiring. At the CIRCUIT level it is typically a loose termination in a switch, a fixture or an outlet on that circuit, or a large motor sharing it. At the PANEL AND SERVICE level it is a loose or corroded connection at the main lugs, the meter, or the service entrance — and that is the category worth acting on quickly. At the UTILITY level it is PG&E's side of the meter, and your neighbours will usually be seeing it too.
The single most useful observation you can make before anyone comes out is HOW MUCH of the house flickers, and whether it is getting worse. One fixture that has always done it is a different problem from every light in the house dipping when the heat pump starts, and a different problem again from something that began three weeks ago and has been worsening since.
Level one: the bulb or the fixture
If the flicker is confined to one fixture, start here, because it costs nothing. Put the suspect bulb in a different fixture and a known-good bulb in the suspect one. If the flicker follows the bulb, you have found it.
If the fixture is on a dimmer and the bulbs are LED, that combination alone explains most flicker in modern homes. Old dimmers were designed for incandescent bulbs drawing 60 to 300 watts, and they regulate by chopping the waveform in a way that assumes a substantial, forgiving load. An LED drawing eight watts gives them almost nothing to work with, and the result is visible flicker or a buzz, particularly at low settings. The fix is a dimmer specifically rated for LED loads, bulbs marked dimmable, and — this part gets skipped — the same brand and model of bulb throughout a single fixture, because different drivers respond differently to the same signal.
Level two: the circuit
If several fixtures flicker together, or the flicker tracks something switching on elsewhere in the room, the circuit is the suspect rather than anything you can screw in. Two things dominate here. The first is a loose termination — a backstabbed outlet, a switch terminal that was never fully tightened, a wire nut that has worked loose over decades of expansion and contraction. The second is a shared circuit carrying a motor: a fridge, a well pump, a workshop compressor. Motors draw several times their running current at startup, and on a circuit that is already loaded that shows up as a visible dip.
A brief dip when a motor starts is normal. A deep one, a long one, or one that is getting worse is not, and the difference is worth measuring rather than guessing at. Flicker that only appears in cold weather deserves a mention here too: connections move as they change temperature, and a joint that is marginal at room temperature can open and close as it cools. Cold-weather-only symptoms point fairly strongly at a loose connection somewhere.
Level three: the panel and the service
When the WHOLE house flickers together, the cause is something everything shares — the main breaker, the main lugs, the meter, or the service entrance conductors. This is the category that justifies a same-day call, and the reason is worth understanding.
A residential service here is 120/240 volts split into two legs that share a neutral. The neutral is what holds each leg at 120 volts no matter how unevenly the two are loaded. If that neutral connection loosens or corrodes, the legs stop being held apart evenly: the lightly loaded side climbs ABOVE 120 volts while the heavily loaded side falls below. The symptom is distinctive — lights brightening in one part of the house while dimming in another, often shifting as appliances cycle on and off. It matters because it is one of the few electrical faults that damages equipment across an entire house rather than in one spot. If several unrelated electronics have failed recently alongside flickering, say so when you call, because it changes what we look for first.
The other service-level cause is simply heat. A loose lug makes resistance, resistance makes heat, and heat makes the connection worse — the same self-feeding cycle that makes old panels dangerous. That is why a warm panel cover alongside flicker is not something to monitor and see how it goes.
Level four: the utility
If your neighbours' lights are flickering at the same time as yours, the problem is on PG&E's side of the meter and it is theirs to fix. Call them. It is still worth having your own service connection checked once they have finished if the flicker persists, because a marginal connection on your side can hide behind a supply problem and outlast it.
When it stops being an annoyance
Any one of these is enough to stop and call rather than continue troubleshooting:
- The whole house flickers or dims together, especially as appliances cycle
- Lights brighten in one part of the house while dimming in another
- A burning smell, or warmth you can feel through the panel cover
- Buzzing or crackling from the panel, a switch, or a fixture
- Flicker that has been getting noticeably worse over days or weeks
- Several unrelated electronics have failed recently
Do not open the panel to look. The cover is the only thing between you and conductors that stay live with every breaker off. If you can smell burning right now, or see smoke or sparking, call 911 first.