LED downlight remains on after switch is turned off

Question

So for the past week or so now, when I turn the switch off for the down lights in the hallway, one of them which is an LED downlight begins to flicker a few times and remains on for about 5 seconds then decides to turn off. None of the other downlights do this, it's just this one. No one has fiddled with any switches, lights and no one has been in the roof so I'm not sure what the issue could be. I'm worried about an electrical fault which may result in a fire, etc....

Your help would be greatly appreciated,

Thanks,

Will

Answer 1

It could be the bulb circuitry going bad. LED lights are different in that most of the "bulb" is actually voltage conversion and a simple circuit system to regulate the LEDs.

This is just an educated guess, but what it sounds like is there's a capacitor inside that still has power in it. The light bulb itself probably has something that senses when the power is turned off and turns the LEDs off via software, letting the capacitor just lose voltage through attrition. If that part of the bulb stopped working, that capacitor could still power the LEDs for a few seconds before running out of power.

You can test this theory in a regular lamp. Just turn it on for a minute, then turn it off. I don't know that it's dangerous to let it keep on doing this (it's probably been doing it like this all along, just with the cutoff working), it's just not expected behavior. If it doesn't overheat in the lamp I wouldn't worry about it.

Answer 2

I'm not sure if the OP is still looking at this question, but I believe what's happening is that the lamp's components have lost their physical contact to the heat sink. When the switch is turned off, it takes those five or so seconds for the LEDs to cool off sufficiently to stop glowing. Yes, I know; LEDs do not generate light by glowing hot enough to emit EM radiation in the visible spectrum, but they do get hot. When you turn off an LED lamp, you'll see that it emits an afterglow for a few hundred milliseconds afterward; without a heat sink it is taking that lamp much longer than a few hundred milliseconds. That light should definitely be replaced, though if I'm right, it has probably failed by now anyway.

Edit: I was going to delete this but later realized the answer isn't wrong; it's just incomplete.

A white LED lamp generates white light by emitting blue light. It then has phosphors that emit red and green light when excited by the blue light. In this particular case those phosphors remain thermally excited after the power is turned off because of the faulty heat sink connection.