What is this?
A light stuck on dim or glowing faintly can have several causes. If the light will not go above a low brightness when the switch is on, the dimmer switch may be faulty or set incorrectly. If the LED bulb glows faintly when the switch is off (known as 'ghosting'), a small leakage current is passing through the circuit — this is very common with LED bulbs on circuits that were originally wired for incandescent bulbs. The leakage is typically caused by two-way switch wiring, illuminated switches, or proximity to other cables inducing a small current.
Common causes
- Dimmer switch set to minimum or the dimmer mechanism has failed
- LED ghosting — small leakage current causing a faint glow when switched off
- Illuminated or neon indicator switch leaking current through the LED
- Incompatible dimmer switch not delivering full power to the LED bulb
- Partially failed LED driver inside the bulb limiting brightness
Is it dangerous?
This is generally low risk. LED ghosting (faint glow when off) is an annoyance rather than a danger — the current involved is tiny. However, if the light is dim when it should be at full brightness and the wiring is warm, there could be a loose connection limiting the current flow, which is a fire risk. Check the switch faceplate temperature.
Can I fix it myself?
If the light is on a dimmer, check the dimmer is turned up fully and the minimum level trim (if fitted) is set correctly. If the LED glows faintly when the switch is off, try a different brand of LED bulb — some are more susceptible to ghosting than others. An LED bypass capacitor (a small device fitted at the light fitting) can absorb the leakage current and stop ghosting. If the light is genuinely dim at full power, try a new bulb first.
When to call an electrician
Call an electrician if a new bulb does not resolve low brightness (suggesting a wiring fault), if you want a bypass capacitor fitted at the light fitting, if the dimmer needs replacing, or if the switch is warm to the touch (suggesting a loose connection).
What will an electrician do?
Test the circuit to determine why the light is not receiving full power
Check for loose connections that may be limiting current flow
Fit a bypass capacitor at the light fitting to resolve LED ghosting
Replace an incompatible dimmer with a suitable LED trailing-edge model
Test the wiring for induced voltages from adjacent cables
Typical cost
£50 – £130
Fitting a bypass capacitor is a quick, low-cost fix. Dimmer replacement or fault-finding in the circuit will cost more.
