LED lights up - what is the cause?

When LED lamps never go out completely, but always glow, that's more than annoying. After all, the afterglow consumes electricity. In this article you will find out what causes are possible, where to look for errors, and how to fix them.

Causes of the afterglow

There is hardly any defect in the LED light. Rather, it behaves in such a way that the LED lamp indicates an error in the installation.

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Sensitivity of LEDs

LEDs can cope with very little power and very low voltages. If there is even a minimal amount of voltage on the lamp, it will be activated. A light bulb, on the other hand, would need a lot more voltage to glow. In this case only the very sensitive LED indicates the problem.

Voltage on the lamp

Voltage can still be applied to the lamp even when it is switched off. This can be caused, for example, by the control wire of a switch (glow switch with lighting). The minimum voltage that is required for the glow light induces an even lower voltage on the LED. The LED light then activates and glows or flashes.

Other causes can be:

  • Unsuitable dimmer (not suitable for the LED light)
  • electromagnetic induction from a cable close to the lamp
  • Older type of follow-up relay

Electromagnetic induction means that the electromagnetic field from a nearby cable induces a tiny voltage on the nearby lamp. This minimum voltage is also already sufficient to cause the glow.

With older follow-up relays it can happen that a minimal control voltage is still applied even in the OFF state. This can be remedied by exchanging the relay; the same applies to an unsuitable dimmer.

Otherwise, the easiest way to remedy this (by a specialist) is to connect a large resistor in front of the lamp, which must be flowed through in the OFF state and thus prevent the build-up of voltage. It only works when there is no electricity, i.e. after the lamp has been switched off.

Tips & Tricks Afterglow and short flashes when switched off indicate the same cause. Dimmable LEDs glow, while non-dimmable LED lights only flash briefly and then go out again. In both cases there is a minimal voltage present.