LED lights up - what's the cause?

If LED lamps never go out completely, but always light up, that is more than annoying. Afterglow, after all, power is consumed. What causes it, where to look for bugs, and how to fix them can be found in this post.

Causes of afterglow

A defect in the LED light is here in almost no case. It behaves rather so that the LED lamp indicates an error in the installation.

Sensitivity of LEDs

LEDs are already able to cope with very little power and very low voltages. If there is even a minimal voltage on the light, it activates. A light bulb, on the other hand, would require much more voltage to glow. In this case, only the very sensitive LED will indicate the problem.

Voltage on the lamp

Even when switched off, voltage can still be applied to the lamp. This can be caused for example by the control wire of a switch (glow switch with lighting). The minimum voltage required for the glowing light induces a much smaller voltage across the LED. The LED light then turns on and glows or flashes.

Other causes can be:

  • unsuitable (not suitable for the LED light) dimmer
  • electromagnetic induction by a cable near the lamp
  • Overrun relay of older design

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

In the case of older follow-up relays, it may happen that a minimum control voltage is applied even in the OFF state. This can be remedied by replacing the relay; the same applies to an unsuitable dimmer.

Otherwise, the easiest way to remedy (by the expert) by switching a large resistance in front of the lamp, which must be traversed in the OFF state and thus prevents the build-up of the voltage. It works only in the state without electricity, so after switching off the lamp.

Tips & Tricks

Afterglow and short flash when switched off indicate the same cause. Dimmable LEDs glow, while non-dimmable LED lights flash only briefly and then go out again. In both cases, it is a minimum applied voltage.

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