Flickering lights are one of those problems that can range from completely harmless to genuinely dangerous. I'm Sam from City Power Electrical Services (ECRA/ESA #7015314), and I troubleshoot flickering lights across the GTA regularly. Here's how to figure out what's causing yours and when you need to call an electrician.
Cause 1: A loose or failing light bulb. This is the simplest and most common cause. Turn off the light, wait for the bulb to cool, and make sure it's screwed in tightly. For LED bulbs, check that the bulb is properly seated in the socket. If the bulb is old, it may simply be failing — LED bulbs can start flickering near the end of their lifespan, especially cheap ones with poor driver circuits.
The fix: Replace the bulb. If the flickering stops, you're done. If it continues with a new bulb, the issue is deeper.
Cause 2: Incompatible dimmer switch. This is extremely common and I see it weekly. If you replaced incandescent bulbs with LEDs but kept the old dimmer switch, flickering is almost guaranteed. Traditional dimmers were designed for incandescent bulbs (which are purely resistive loads). LEDs have electronic drivers that behave differently, and an incompatible dimmer causes flickering, buzzing, and sometimes a reduced dimming range.
The fix: Replace the dimmer with an LED-compatible dimmer. Lutron, Leviton, and Legrand all make dimmers specifically designed for LED loads. A quality LED dimmer costs $30 to $80 and takes about 30 minutes to install. Also check the LED bulb manufacturer's compatibility list — not all LED bulbs work with all dimmers, even LED-rated ones.
Cause 3: Voltage fluctuation from large appliances. If your lights dim or flicker briefly when your furnace kicks on, the AC compressor starts, or the dryer starts a cycle, you're seeing voltage fluctuation from a large motor starting up. The motor draws a surge of current for a fraction of a second, which momentarily drops the voltage on the circuit (and sometimes on other circuits sharing the same panel bus). A brief, slight dimming is normal and usually harmless.
However, if the dimming is severe (lights drop to half brightness), prolonged (more than a second), or happens frequently, it could indicate undersized wiring, a poor connection in the panel, or a panel that's struggling with the total load. If your air conditioner causes significant dimming throughout the house every time it cycles, that's worth investigating.
Cause 4: Loose wiring connections. This is the cause that concerns me the most. A loose connection anywhere in the circuit — at the panel, at a junction box, at a wire nut splice, at an outlet, or at the light fixture itself — creates resistance. Resistance creates heat. And heat at an electrical connection is the beginning of an electrical fire.
Loose connections can cause intermittent flickering because the connection makes and breaks contact as the wires shift due to thermal expansion, vibration, or simply gravity. The flickering might come and go over weeks or months, gradually getting worse.
If your lights flicker and you've ruled out bulbs and dimmers, and especially if the flickering is accompanied by a warm or discoloured switch plate or outlet cover, a buzzing sound from the wall, or a burning smell, call an electrician immediately. This is not a wait-and-see situation.
Cause 5: Aluminum wiring connection issues. If your GTA home was built between 1965 and 1976, it likely has aluminum branch circuit wiring. Aluminum wiring connections are prone to loosening over time due to aluminum's tendency to expand and contract more than copper. Flickering lights are a classic symptom of deteriorating aluminum wiring connections.
The fix for aluminum wiring issues is remediation using approved AlumiConn or COPALUM connectors at all connection points. See my article on aluminum wiring remediation for details. This is not a DIY job — it must be done by a licensed electrician.
Cause 6: Utility service issues. If the flickering affects your entire house (not just one circuit) and is random, the problem might be on the utility side. This could be a poor connection at your meter, a problem with the utility transformer serving your neighbourhood, or an issue with the service drop (the cable from the pole to your house).
To determine if it's a utility issue, check whether your neighbours are experiencing the same thing. If they are, report it to your utility company (Toronto Hydro at 416-542-8000, or your local provider). If it's only your house, the issue is likely at your meter base, your service entrance, or your panel — and that's something I can diagnose and fix.
A note about flickering throughout the entire house. If all the lights in your home flicker simultaneously (not just one room), the problem is at the main service point — the utility connection, the meter base, the service entrance cable, or the main breaker. These are all high-amperage connections where a loose or corroded connection can be very dangerous. Don't ignore whole-house flickering.
Here is my recommended diagnostic approach. Step one: check the bulb (tighten or replace). Step two: check the dimmer compatibility. Step three: notice the pattern — does it happen on one circuit, one room, or the whole house? Does it correlate with an appliance cycling? Step four: if it's limited to one circuit and persists after checking bulbs and dimmers, call an electrician to check connections. Step five: if it's whole-house, call an electrician promptly — don't wait.
If your lights are flickering in your GTA home, call City Power Electrical Services at 416-877-3048. I'll find the cause and fix it. Most flickering light issues can be diagnosed and resolved in a single visit.