LED downlights flicker mainly because the dimmer and the LED driver are mismatched. LEDs draw so little power that a dimmer built for halogen lamps cannot hold a steady output, so the light pulses. Other common causes are a non-dimmable lamp fitted to a dimmer circuit, an old halogen transformer left in place, or a loose connection at the fitting.
Almost all downlight flicker is a compatibility problem rather than a dangerous one. The exception matters though, and the difference is easy to spot once you know what to look at.
What makes an LED downlight flicker when the old halogen never did?
A halogen lamp glowed by heating a filament, and that filament smoothed out every dip in the power feeding it. An LED has no filament and no thermal lag. It follows the supply almost instantly, so any interruption shows up as visible flicker instead of being absorbed.
The second half of the answer is load. A halogen downlight drew about 50 watts. The LED replacing it draws around 7 to 10 watts, so ten of them turn a 500 watt circuit into one under 100. Most dimmers were designed around the old number and misbehave well below it.
Is the dimmer the problem?
In most Sydney homes we attend for flickering downlights, the dimmer is the cause. Two things go wrong.
The dimmer type is wrong. Older dimmers are leading edge, built for halogen lamps and iron core transformers. LED drivers generally want a trailing edge dimmer. Run LEDs on a leading edge dimmer and you get flicker, buzzing, a narrow dimming range, or lamps that will not start at low settings.
The dimmer never reaches its minimum load. Every dimmer has a lowest wattage it can control, often around 20 to 40 watts. Three 7 watt LEDs total 21 watts, right at the edge. Below that threshold the dimmer cannot regulate and the output wanders.
Mixing brands adds to it. Two drivers on the same dimmer read the same signal differently, so one lamp can flicker while its neighbour looks fine.
Why do my downlights flicker only when they are dimmed?
Flicker that appears only at low brightness and clears at full output points at the dimmer, not the lamps. As you dim, the dimmer chops more of the waveform away, and once the driver has too little left to hold a steady output, the light pulses.
The fix is usually a swap to an LED-compatible trailing edge dimmer, matched to the wattage on the circuit. Occasionally the lamps are the limit, because budget drivers dim badly whatever controls them.
Do you still have a transformer above the ceiling?
If your LEDs were fitted as a lamp-only swap, the original halogen transformer is probably still sitting in the ceiling. Halogen downlights ran at 12 volts through a transformer beside each fitting. Change only the globe to a 12 volt LED and it is fed by a device built for a load five times larger.
Iron core transformers are the worst offenders and they hum as well as flicker. The proper repair is to remove the transformer and fit a mains voltage LED downlight with its own driver, as modern fittings are built.
Flickering that a new dimmer will not fix?
DM Electrical works residential lighting across the Northern Beaches, North Shore, Eastern Suburbs and wider Sydney from our base in Brookvale. If the flicker has spread past one fitting, we will find the cause and tell you what it needs.
When is flickering a wiring fault instead of a fitting problem?
Where the flicker shows up is the best clue you have. One fitting means the fitting, a whole circuit means the wiring, and the whole house means the supply.
A single downlight flickering on its own is the lamp, its driver, or the connection at that fitting. A whole run flickering together, particularly with a buzz at the switch, points at the dimmer or a loose connection in the circuit. Lights dimming across several rooms when the air conditioner starts is a load or supply issue. If that is happening, read our guide to the urgent signs you need an emergency electrician, because flicker across multiple rooms can mean a failing neutral rather than anything to do with your lights.
Treat flicker as urgent if it arrives with a burning smell, a warm or discoloured switch plate, a buzzing switchboard, or if the circuit also trips its breaker. That is a job for an emergency electrician, not next week.
Flicker patterns and what usually causes them
| What you are seeing | Most likely cause | What it usually needs |
|---|---|---|
| Flickers only when dimmed, steady at full | Leading edge dimmer, or load below its minimum | Trailing edge LED dimmer, sized to the circuit |
| One lamp flickers, the rest are fine | Failing driver or a loose connection at that fitting | Replace the fitting, or remake the connection |
| Flickers and hums from the ceiling | Halogen transformer left in after a swap | Remove transformer, fit mains voltage downlights |
| Whole run pulses together, buzz at the switch | Dimmer fault or loose connection in the circuit | Circuit inspection and repair |
| Lights dip across rooms when appliances start | Load, or a failing neutral on the supply side | Inspection promptly, treat as urgent |
| New lamps flicker even without a dimmer | Non-dimmable lamps on a dimmer, or poor drivers | Correct lamp choice, or bypass the dimmer |
What can you check before calling an electrician?
Two checks are safe to do yourself and they narrow it down fast. Turn the dimmer to full and watch: if the flicker stops, the dimmer is involved. Then check whether the lamps are marked dimmable, because non-dimmable LEDs on a dimmer circuit will flicker however good the dimmer is.
Beyond that, changing a plug-in lamp is fine, but replacing a dimmer, removing a transformer, or opening a ceiling connection is licensed electrical work in New South Wales and has to leave a compliance certificate behind. If your downlights date from a renovation, it is worth reading whether your house needs rewiring, since lighting circuits in older homes often have no earth and cannot take metal fittings safely.
Frequently asked questions
Do LED downlights need a special dimmer?
Yes, in almost every case. LEDs need a dimmer marked as LED compatible, which is usually a trailing edge type, and it has to be rated for the low total wattage the lamps actually draw. An old halogen dimmer left on an LED circuit is the single most common cause of flickering downlights.
Is a flickering downlight dangerous?
A single downlight flickering on its own is almost always a lamp or driver problem rather than a hazard. It becomes urgent if the flicker spreads across rooms, comes with a burning smell, a buzzing switchboard, or a warm switch plate, or if the circuit trips as well. Those signs suggest a loose connection or a supply fault and should be looked at promptly.
Can I fix flickering LED downlights myself?
You can swap a plug-in lamp and you can test whether the flicker follows the dimmer setting. Replacing a dimmer, removing a halogen transformer, or working on the wiring at the fitting is licensed electrical work in New South Wales and has to be done by a licensed electrician who issues a compliance certificate.
Why do my downlights flicker when the air conditioner starts?
A brief dip as a large appliance starts is normal, because the motor draws a surge of current for a moment. A dip that is deep, lasts more than a second, or happens across several rooms suggests the circuit is undersized or a connection is failing, and that is worth an inspection rather than ignoring.
The bottom line
Flickering LED downlights are usually a mismatch between old dimming gear and new low wattage lamps, and the repair is normally a trailing edge dimmer or the removal of a leftover halogen transformer, and neither is a big job. What is worth taking seriously is flicker that spreads beyond one circuit, arrives with heat or a smell, or comes with a tripping breaker, because that is a wiring or supply fault showing up in the lights. DM Electrical handles residential lighting and fault finding across Sydney, 24/7. Get in touch and we will tell you which one you have.