Lights Flickering in the House? How to Find the Cause

Before anything else, count how many lights are doing it. A single lamp that flickers and a whole house that flickers are separate problems. They have different causes, different fixes and sometimes a different person to call.

The Electrical Safety Authority (ESA) homeowner handbook names three places the trouble can start. Dim, surging or flickering lights can be a sign of a loose connection in a lighting circuit, in a fixture, or in your electrical service. Those three line up well with the patterns below. Sources are linked under the article.

Why are my lights flickering? Count the lights first

One fixture. If a single lamp or ceiling light flickers while everything else in the room stays steady, begin with the parts only that light has: its bulb, how the bulb sits in the socket, the dimmer controlling it, and the fixture itself.

One switch or one room. When several lights on the same switch or in the same area flicker together, look past the bulbs to what they share. That could be the dimmer, a connection in a box somewhere along the circuit, or the circuit's terminal at the panel.

Every room at once. Flickering or dipping throughout the house points at what feeds the whole home: the service connection, the main panel or the utility's supply. A large appliance starting up can also cause a brief flicker, which comes up again further down.

Keep notes for a few days: which lights, what time of day, and what else was switched on. Patterns show up quickly, and they save time once someone is testing circuits.

How to fix flickering lights when it is one fixture

Start with the bulb. It costs the least to rule out, and it is the one part you can safely handle yourself. Philips lists a loose physical connection among the causes of LED flicker, where the bulb isn't screwed tightly into the socket or the fixture wiring is loose. Its advice is to turn off the power and make sure the bulb and fixture are secure.

If tightening it changes nothing, put in a bulb you know works. When the flicker follows the old bulb into another lamp, the bulb is the problem. When it stays with the fixture even with a good bulb, the fault sits in the socket, the switch, the dimmer or the wiring behind them. That is where homeowner checks end, because opening a fixture, a switch box or a ceiling box is electrical work under ESA's rules, covered below.

If the light is on a dimmer and the bulb is an LED, read the next section before blaming the wiring.

Why do LED lights flicker on a dimmer?

When LED lights flicker on a dimmer, the first thing to question is whether the bulb and the dimmer suit each other. Leviton puts it plainly: LED bulbs use a similar technology but are not engineered the same, and performance may vary with different dimmers. Natural Resources Canada makes the same point from the other direction, noting that the dimmer switch must be compatible with the type of bulb.

The manufacturers describe a handful of common mismatches.

The bulb is not dimmable. Lutron warns that many LEDs are not dimmable, smart or connected bulbs included, and tells owners to check the packaging for wording such as "non-dimmable" or "Not for use with dimming devices".

The dimmer was made for incandescent bulbs. Philips says traditional incandescent dimmers often produce poor results with LEDs, leading to uneven dimming or flickering, and recommends dimmers labelled LED-compatible, MLV (magnetic low voltage) or ELV (electronic low voltage).

The flicker only shows up near the bottom of the range. Lutron's explanation is that the LED may not dim as low as the dimmer does, and its troubleshooting article walks through a low-end trim adjustment for it. On its Decora Smart dimmers, Leviton suggests setting the minimum level about 1% above the point where flickering begins. Both are settings on the dimmer itself, made by following the maker's instructions.

The lights glow or flicker after they are switched off. According to Lutron, a small amount of electricity may still flow through the dimmer and the LEDs, and in rare cases, particularly with older LED technology, that can make lights glow or flicker even though they are off.

The flicker happens at every level. Leviton notes that wiring one of its smart dimmers without a neutral may cause the bulb to flicker at all levels and keep the dimmer from working properly. Finding out whether the box has a neutral, and changing the dimmer, are jobs inside the wall.

To avoid buying the wrong bulb twice, check the pairing first. Leviton's LED Compatibility Selector Tool, for example, lets you pick the dimmer you have and shows the bulbs that work with it.

Pot lights flickering or flashing

Recessed lights bring a few problems of their own, and several of them involve the dimmer.

A flash at switch-on. Cooper Lighting's dimming guide for its Halo RL downlights explains that some LED dimmers use a "rapid start" design to give lamps a momentary power boost during start-up, and that the boost may cause a momentary flash. The guide says the flash is generated by the dimmer and may be more noticeable at a low setting. It names Eaton dimmers that let the rapid start be adjusted.

Two dimmers on one set of lights. Where pot lights are switched from two locations, the controls have to be chosen as a set. Lutron's troubleshooting article for its Maestro LED+ dimmers says only one of those dimmers can be installed in a lighting circuit, and it lists two LED+ dimmers on the same lights as a cause of flickering or flashing.

The fixture's own compatibility list. Downlight makers such as Halo and Juno publish dimmer compatibility guides for their fixtures. Check the one for the model in your ceiling before buying a new dimmer.

Low-voltage pot lights, the kind fed through a transformer, add one more part to match. Lutron's white paper on dimming LEDs on low-voltage transformers says poor dimming behaviour of this kind is sometimes blamed on dimmer compatibility when it is often a symptom of compatibility problems between the LED and the driver or transformer.

Multiple lights flickering in house: what it can point to

Several rooms flickering together is a different conversation, and a new bulb will not settle it.

A big appliance starting. Oshawa Power's FAQ says an appliance with a motor or compressor, such as a refrigerator, freezer, dryer or washing machine, can make the lights flicker for a brief instant as it starts, and calls that perfectly normal. Ottawa Fire Services, for its part, lists lights that dim when certain appliances are used among the signs that a home should be inspected by a certified electrician. A blink as the fridge kicks in is one thing. Lights that sag every time the dryer or a space heater runs are another.

A loose connection upstream. ESA's handbook names your electrical service among the places a loose connection can cause dim or surging lights. The neutral conductor belongs in that picture. ESA's guideline on residential services damaged in emergencies says neutral continuity must be assured, and warns that loss of neutral continuity may create dangerous voltage imbalances on the consumer's service and distribution equipment.

Aluminum branch wiring. ESA's flash notice on aluminum wiring lists flickering lights, together with warm cover plates, discoloured switches or receptacles, signs of arcing and a smell of hot plastic insulation, as possible evidence of failing terminations. ESA's aluminum wiring page says a home built between the mid-1960s and late 1970s may have it. The same notice warns that aluminum-wired connections have been known to fail and overheat without any prior indications, so steady lights are no proof that the connections are sound.

None of these can be judged by eye from the hallway. ESA's handbook is direct: if you detect dim, surging or flickering lights in your home, contact a Licensed Electrical Contractor.

Is the flicker coming from the utility?

Sometimes the cause sits outside the house. Oshawa Power's conditions of service state that the nature of an electrical supply system is such that periodically there will be voltage fluctuations and other disturbances which can cause flickering lights. Its FAQ asks customers whose lights flicker continually throughout the entire house, or who have power in only part of the house, to call its office. A Customer Service Representative may then refer them to its Technical Services department.

Toronto Hydro's outage report form has a separate choice for lights that are flickering or dimming. Its momentary outages page asks anyone with flickering lights, partial power or other outage-related issues to report online or by phone. For partial power, its outage advice suggests a few checks first: if only part of your home is without power, you might have an internal electrical issue, so unplug appliances that might be overloaded, reset the Ground Fault Interrupter (GFI) switch and check your panel for tripped breakers. The report form adds that when only part of a home is without power, a qualified electrician may resolve the issue more quickly.

In other service areas, use your own distributor's outage line or website. Before you report, note whether neighbours on the street are seeing the same thing.

What you can check yourself, and what needs a licensed electrician

The homeowner list is short:

1. Keep a log of which lights flicker, when, and what else was running. 2. With the power off, make sure each bulb is screwed in firmly. 3. Read the bulb packaging and the dimmer label to confirm they are meant to work together. 4. Use the dimmer's own adjustment, if it has one, following the manufacturer's instructions. 5. For partial power, unplug anything that might be overloaded, reset the GFI and look for a tripped breaker, as Toronto Hydro suggests.

Everything past that is electrical work: replacing a dimmer or switch, opening a fixture or junction box, tightening connections, and anything inside the panel. ESA lets homeowners do electrical work in their own home, but they must file a notification with ESA and must not conceal the work before ESA has reviewed it. Nobody else can do it on your behalf, ESA adds, not even a friend, relative or neighbour. If you hire someone, ESA says that by law it must be a Licensed Electrical Contractor, and you should look for its 7-digit ECRA/ESA licence number.

When flickering lights are urgent

Some signs mean the troubleshooting stops. In its notice on aluminum wiring, ESA lists warm cover plates, discoloured switches or receptacles, signs of arcing and the smell of hot plastic insulation next to flickering lights as possible evidence of overheating terminations. Heat, a burning smell or sparking at a switch, receptacle, fixture or the panel calls for a Licensed Electrical Contractor right away, not another bulb.

Smoke or flames mean getting everyone out and calling 911. Ontario's fire safety advice is to call the fire department from outside your home instead of wasting valuable seconds calling from inside.

If a storm brings a wire down, keep clear of it. Elexicon Energy tells customers to always treat downed power lines as live and dangerous, and to call 9-1-1 and the utility immediately to report downed wires or electrical hazards. For an outage or a problem with the supply, call your local utility.

KV Bear Electrical (ECRA/ESA 7014730) can find the cause, whether it turns out to be a dimmer that does not suit its LEDs or a loose connection at the panel. Urgent calls get priority during business hours only: Monday to Friday 7am to 6pm, Saturday 8am to 2pm. Call 905-999-5048 or request a quote.