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.
Safety first
Isolate at the switchboard and prove dead before opening a fitting. Lighting points can have active, neutral, and switch wires in the same ceiling rose — don't assume which is which.
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
Failed lamp / globe
Most likelyThe simplest and most common cause — the globe or LED has reached end of life or failed.
- 2
Faulty LED driver / integrated fitting
#2On integrated LED fittings the driver fails rather than a replaceable globe.
- 3
Loose connection at the fitting or switch
#3A loose terminal at the rose, fitting, or switch breaks supply to that one point.
- 4
Faulty light switch
Least likelyThe switch for that light isn't making, so the point never energises.
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.
Swap in a known-good globe (for fittings with a replaceable lamp).
The light works with a known-good globe.
It was just the globe — done.
Still dead — isolate and check supply at the fitting/switch.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
One light not working
→ step 2 - 2decision
Does a known-good globe fix it?
Yes→ step 3No→ step 4 - 3result
It was the globe — done.
- 4decision
Are the connections at the fitting and switch sound?
Yes→ step 5No→ step 6 - 5decision
Does the switch make and the fitting/driver test healthy?
Yes→ step 7No→ step 8 - 6result
Loose/broken connection — remake it.
- 7result
Re-check lamp/fitting compatibility.
- 8result
Faulty switch or fitting/driver — replace it.
Common mistakes apprentices make
- Replacing the whole fitting before trying a known-good globe.
- Not isolating before opening a ceiling rose with multiple wires.
- Assuming the switch when it's actually a failed LED driver.
- Overlooking a loose neutral shared at the rose.
When to stop & escalate
Domestic electrical work is restricted to licensed electricians — fault-finding within fixed wiring, fittings, or switches must be done by a licensed person. If only one of several lights on a shared rose is affected, check the others aren't about to follow.
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.
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.
No supply at a socket-outlet or point
A socket-outlet or point is dead — nothing plugged in works — while other points may be fine. A bread-and-butter 'trace it back' fault.
Learn the theory
How the gear and circuits behind this fault actually work.