Why do my lights stay on faintly even after I turn the switch off?

Lights that glow faintly or stay slightly illuminated after the switch is turned off — sometimes called "ghosting" — is almost always caused by a small amount of residual current leaking through the circuit, and it is overwhelmingly an LED-specific issue. Incandescent bulbs need substantial current to produce visible light, so tiny leakage currents go unnoticed. LED bulbs, however, are so energy-efficient that even a few milliamps of stray current is enough to produce a faint glow.

The most common cause is an illuminated or smart switch. Switches with a built-in indicator light — a small LED or neon glow lamp that shows the switch location in the dark — work by passing a tiny trickle of current through the light fixture circuit to power that indicator. With incandescent bulbs, this trickle was invisible. With LED bulbs, it is enough to produce a noticeable ghostly glow. If you recently upgraded to LED bulbs and now notice faint glowing, check whether your switch has a locator light. The solution is either to replace the switch with a standard non-illuminated switch or to install a small resistor (sometimes called an LED minimum load device or "LED killer") across the fixture, which absorbs the trickle current. These devices cost $10-$15 and are wired at the light fixture.

Smart switches and electronic dimmer switches can cause the same effect. Most smart switches require a small amount of standby current to power their WiFi or Z-Wave radio and their internal electronics. In a properly wired switch box with a neutral wire, the smart switch draws standby power from the neutral and the problem does not occur. But in many older GTA homes — particularly pre-1980s houses in established Toronto neighbourhoods — the switch box has no neutral wire. Some smart switches designed for no-neutral installations complete their standby circuit through the light fixture, causing a faint glow in LED bulbs.

Another cause is capacitive coupling in the wiring. When the wire running to the switch and the wire running to the fixture are bundled together in the same cable or conduit for a long run, a small amount of electrical energy can transfer between them through capacitive coupling — similar to how two wires running parallel act like a tiny capacitor. This induced voltage is enough to faintly illuminate an LED bulb. This is more common on long wire runs in larger homes and is a characteristic of the wiring installation rather than a fault.

A less common but more concerning cause is a miswired switch. If the switch is breaking the neutral wire instead of the hot wire — a wiring error that violates the Ontario Electrical Safety Code — the fixture remains connected to the hot wire even when the switch is off. The full 120 volts is present at the fixture terminals, and any leakage path to the neutral (through residual capacitance in the wiring or moisture) will produce a glow. More importantly, a neutral-switched fixture is a shock hazard because the socket remains energized when you think the light is off. If your lights glow faintly and you are not sure about the wiring, have a licensed electrician verify that the switch is breaking the hot wire.

In most cases, LED ghosting is a nuisance rather than a hazard, and it can be resolved with a switch replacement ($150-$250 installed), a minimum load resistor at the fixture ($10-$15 plus installation), or in some cases simply trying a different brand of LED bulb — some LEDs are more susceptible to ghosting than others. If you suspect a wiring issue rather than a simple LED compatibility problem, a licensed electrician can test and verify proper switch wiring. Browse electrical professionals through the Toronto Construction Network directory to find someone who can sort it out.