Dimmer buzzing or LEDs not dimming smoothly
A dimmer buzzes, the LEDs flicker/strobe at low levels, won't go very low, or some lamps glow when 'off' — typically an LED/dimmer compatibility issue.
Safety first
Isolate before changing a dimmer or lamps. A buzzing dimmer running hot should be addressed, not left.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
LED not matched to the dimmer type
Most likelyOlder leading-edge dimmers and non-dimmable or mismatched LEDs cause buzz, strobe, and poor low-end dimming.
- 2
Load below the dimmer's minimum
#2LEDs draw little power; a few lamps can fall below the dimmer's minimum load, causing flicker or glow.
- 3
Mixed lamp types on one dimmer
#3Different LED brands/models on one dimmer behave inconsistently.
- 4
Faulty dimmer
Least likelyThe dimmer itself has failed or is the wrong type for the load.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
Check the dimmer type (leading vs trailing edge / LED-rated) against the lamps fitted.
A trailing-edge / LED-rated dimmer suited to the lamps.
Compatible type — check minimum load and lamp consistency.
Mismatch — fit an LED-rated (usually trailing-edge) dimmer.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Dimmer buzz / poor dimming
→ step 2 - 2decision
Is the dimmer LED-rated and matched to the lamps?
Yes→ step 3No→ step 4 - 3decision
Is the load within range and the lamps consistent?
Yes→ step 5No→ step 6 - 4result
Fit an LED-rated (trailing-edge) dimmer.
- 5result
Suspect a faulty dimmer — replace.
- 6result
Below minimum / mixed lamps — adjust load or standardise lamps.
Common mistakes apprentices make
- Using a leading-edge dimmer with modern LEDs.
- Putting too small an LED load on a dimmer (below its minimum).
- Mixing LED brands/models on one dimmer.
- Assuming the LEDs are faulty when it's the dimmer pairing.
When to stop & escalate
Dimmer/lamp selection and replacement is electrical work for a licensed person. If a compatible, correctly-loaded combination still misbehaves, the dimmer or lamps are faulty and should be replaced.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Lights flickering
One or more lights flicker — constantly, intermittently, or when other appliances run. Common with LEDs and dimmers, but can also signal a loose connection.
A single light not working
One light fitting is dead while the rest of the lights on the circuit work fine — points at the lamp, the fitting, or the switch for that point rather than the whole circuit.
Downlights cutting out then coming back
Downlights switch off after a while then come back once cooled — classic thermal cut-out behaviour, usually from heat build-up around the fitting or driver.