If a dimmed circuit works at high brightness and flickers at low brightness, the usual cause is not a fault. There is not enough load connected for the dimmer to regulate.
Why a minimum exists
A dimmer needs a certain amount of current flowing to sense where it is in the mains cycle and to keep its own electronics powered. Below that, its timing becomes unreliable and the light output wanders — which you see as flicker, usually worst at the bottom of the dial where the conduction period is shortest.
With filament bulbs this never came up. A single 60 W bulb comfortably exceeded any minimum.
An LED replacement for that bulb draws around 8 W. A circuit that used to present 180 W now presents 24 W, and older dimmers commonly specify a minimum of 40 W or more.
Add up what you have
Count the actual wattage of the LEDs, not the incandescent-equivalent figure printed in large type on the front of the box.
| Bulbs | Actual wattage | Total |
|---|---|---|
| 3 × 6 W downlights | 6 W | 18 W |
| 6 × 5 W downlights | 5 W | 30 W |
| 2 × 9 W pendants | 9 W | 18 W |
| 9 × 5 W downlights | 5 W | 45 W |
Compare that total against the dimmer's stated minimum for LED loads. If the datasheet gives one figure for incandescent and another for LED, the LED figure applies.
De-rating catches people out
A dimmer marked 400 W is often rated far lower with LEDs — sometimes 100 W, sometimes 60 W. The reason is that LED drivers draw current in short sharp pulses rather than smoothly, and the peak current matters more than the average for the dimmer's switching device.
The consequence is that both ends move: the maximum drops, and the useful minimum is often higher than the printed one. A circuit close to either limit is where marginal behavior lives.
Three ways to fix a shortfall
1. Fit a modern LED-rated dimmer. This is the right answer almost every time. Current trailing-edge LED dimmers commonly work down to a few watts, and many state no practical minimum at all. It is a like-for-like swap in the same backbox.
2. Add more bulbs to the circuit. If a room genuinely wants more light, extending the grid raises the load and improves the lighting at the same time. Working out how many the room should have is in recessed light spacing.
3. Fit a dummy load or bypass. A resistive dummy load module wired at one fitting brings the circuit above the minimum. It works, and it is a workaround rather than a fix — it burns the extra watts as heat, undoing part of the point of LEDs. Reasonable when the dimmer is inaccessible; otherwise fit the right dimmer.
The symptom pattern
| Symptom | Points to |
|---|---|
| Flicker only at low brightness | Below minimum load |
| Flicker across the whole range | Wrong dimmer type, or non-dimmable bulbs |
| Will not dim below about 30% | Bulb driver's own limit |
| Jumps to full at the bottom | Driver restarting from low load |
| Dimmer runs hot | Near the maximum, or de-rating exceeded |
| Faint glow when off | Leakage — needs a bypass at the fitting |
While you are at it
Two other checks belong with this one. The dimmer should be trailing edge for LED loads — see trailing edge vs leading edge — and every bulb on the circuit should be dimmable and the same model, because mixed drivers behave differently on the same waveform.
All four checks together are in LED dimmer compatibility.