Why are my lights flickering?

Before anything else, work out the scope of the flicker. It narrows the cause faster than any other question.

• One light or one dimmer. Almost always the fitting, the globe or the dimmer. Irritating, not dangerous.
• One room or one circuit. Usually a loose connection somewhere on that circuit. Worth getting looked at.
• The whole house, all at once. Upstream of your lights — the main switchboard, the service, or the network. Treat this one seriously.

Then ask a second question: does it flicker when something else turns on? Lights that dip when the air conditioner, pool pump or oven kicks in are telling you about load and voltage, not about the lights.

If your flickering started when you changed to LED globes or downlights, this is your answer nine times out of ten.

The old dimmer expects a much bigger load. A dimmer installed for halogen downlights was designed to control 50 watts per lamp. Swap ten halogens for ten LEDs and the same circuit now draws under a tenth of that. Many older leading-edge dimmers have a minimum load they need to operate smoothly, and below it they stutter — which you see as flicker, shimmer, or lights that won't go fully dark.

The dimmer and the driver disagree. LED drivers and dimmers have to be compatible, and "dimmable" on the box does not mean "dimmable on your dimmer". A trailing-edge dimmer matched to the fitting is the usual fix, and it is a cheap one.

One non-dimmable globe on a dimmed circuit. A single non-dimmable lamp among dimmable ones will flicker and can make its neighbours misbehave too. Check every globe on the circuit, not just the one you can see doing it.

A failing driver. Integrated LED downlights have a driver that fails long before the LED does. A single fitting that flickers on its own, at full brightness, with no dimmer involved, is usually this.

If you are converting halogens or chasing dimming that actually works, that is the substance of our LED downlight page.

Electricity arcing across a connection that has worked itself loose produces heat. Enough of it, in a ceiling space full of insulation and timber, starts fires. This is the reason flickering is worth taking seriously rather than living with.

A loose connection tends to look like this:

• Flicker on one circuit that comes and goes with no pattern you can pin to a dimmer or a globe
• Lights that flicker when you walk heavily past, or when a door slams
• A light that has started flickering in a house where nothing was changed
• Any flicker accompanied by a smell of hot plastic, a warm switch plate or a discoloured socket — turn that circuit off at the switchboard and call an electrician the same day

Connections loosen over time through ordinary thermal cycling. It is not a sign anyone did a bad job; it is a sign the house is old enough to need a look. Older Hills homes with original wiring are the ones we find it in most.

This is the pattern to stop and think about. If lights across several circuits dim or flicker together, the cause is upstream of all of them.

Big appliances starting up. A brief dip when an air conditioner compressor, a pool pump or a bore pump starts is normal-ish — the motor draws a large inrush current for a fraction of a second. A pronounced dip, every time, suggests the supply or the submain is marginal for the load. On acreage with a long run from the street, that is a common finding and a solvable one.

A loose or failing neutral. This is the serious one. When the neutral connection degrades, voltage stops dividing evenly across the house: some circuits get more than 230V and some get less. Lights brighten and dim in opposition, LEDs and appliances fail in clusters, and equipment can be damaged. Signs are lights that get brighter in one part of the house as they dim in another, repeated failures of globes or electronics, and flicker that tracks whatever else is switched on.

If that sounds like your house, don't wait. Turn off what you can and call.

Or it's the network, not you. Before assuming the worst, look outside. If your neighbours' lights are doing it too, it is Ausgrid's or Endeavour's problem, and there may be a fault or planned work in the area. A quick check of their outage page settles it.

1. Swap the globe for one you know works. Free, and it resolves a good proportion of single-light flicker.
2. Screw or seat it properly. A bayonet lamp that isn't fully clicked in, or a downlight not fully engaged, flickers.
3. Take the dimmer out of the equation. Run the circuit at full brightness for an evening. If the flicker disappears, it is the dimmer or the lamp-dimmer match.
4. Note what else is on. Write down what was running when it flickered. That single piece of information often tells us more than anything we can measure on the day.
5. Look at your neighbours. Rules out the network in ten seconds.

Beyond that, stop. Opening a fitting, a switch or the switchboard is licensed work in NSW, and the faults that actually matter here are the ones you cannot see from underneath.