1. A cheap or old LED bulb
Inexpensive LED bulbs have a weak driver (the power supply inside). Over time it starts to flicker. The check is simple: put another bulb in this holder. If the flicker stops, the bulb is to blame.
2. A loose contact in the holder
The centre tab of the holder gets pressed down and touches the bulb poorly. The light flickers, especially if you touch the fitting. Dangerous: a poor contact heats up.
3. A loose twisted joint or terminal
The light’s wires are joined by twisting, or a terminal has loosened. Common with wall lights and old chandeliers. Signs: flickering, a smell of hot plastic, darkening at the joint.
4. An illuminated switch
Does a switched-off LED bulb glow faintly or flash every few seconds? Often the culprit is a switch with a backlight: a small current flows through its indicator. The fix is a switch without a backlight or a different type of bulb.
5. The switch breaks the neutral, not the live
If the wires were mixed up during connection, the bulb stays live even with the light off. The bulb may flicker, and changing it becomes more dangerous. It takes a minute to check with a tester.
6. A dimmer and an unsuitable bulb
Not all LED bulbs work with a dimmer. If there is a dimmer and the bulb is "non-dimmable", it flickers and hums. You need a bulb marked dimmable or an ordinary switch.
7. Voltage fluctuations
If the light flickers throughout the flat, especially when the water heater, air conditioner or washing machine switches on, the problem may be in the wiring or on the supply line. That is no longer a small repair: I can check, but I do not redo the main wiring.
What you can do yourself
- Replace the bulb with one you know works.
- Tighten the bulb in the holder (with the breaker off).
- If the whole flat flickers, note when it happens and tell a technician or the power company.