A LED pendant light with a supermarket own brand 9W bulb is running considerably dimmer than normal. Additionally when switched off it ?fades our? over a second or so (which it never used to do).
Has anyone else seen LED bulbs behave like this? New to me.
Tim
Yes.
Seen all sorts of shit with them. But that is one I have seen.
There is a technical term for it....
Its the power supply that often has an issue, depending on what sort it is. A leaky rectifier for example a capacitor changed in value. They are I think not built to exacting specs!
Brian
most of mine do that, but they didn't just start doing it one day.
If the LED does not conduct as much current as normal (ohmic), the "main capacitor" in the SMPS in the light bulb, is able to pump that tiny current for a number of seconds.
It implies the SMPS is fine, but the LED string has failed and has managed to add resistance to the path. This gives the impression the SMPS is giving power for longer, when it's the LED loading which is less.
Not all bulbs use SMPS. Some use capacitor-dropper as a technique, for which the symptoms could be different. Capacitor-dropper bulbs might not "regulate" the light level, like the SMPS ones do. Capacitor-dropper bulbs, can be damaged by transients on mains. SMPS are much more resistant to that issue.
Paul
Thanks for the explanation. I was just curious.
Tim
Most likely one of the LEDs in the chain has gone high impedance or that there is a resistive dry joint in it. The LEDs all glow dimmer on lower current and the time constant to discharge the PSU capacitor is longer.
The other one I see fairly often on the cheapest and nastiest is a single LED failure in a long chain taking the entire thing out completely. Better ones have two or three LED chains so that you don't lose everything if one solitary LED turns up its toes.
Modern LEDs are so efficient that they sometimes glow when "off" just from the capacitive leakage current from the mains wiring.
Yes, I have a box of dead ones, almost all of the type that has "filament" structures, made by Osram. I don't buy that sort any more. John
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