Curious bulb behaviour
 

A LED pendant light with a supermarket own brand 9W bulb is running
considerably dimmer than normal. Additionally when switched off it €œfades
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

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Curious bulb behaviour
 

On 06/05/2020 20:50, Tim+ wrote:

A LED pendant light with a supermarket own brand 9W bulb is running
considerably dimmer than normal. Additionally when switched off it €œfades
our€� over a second or so (which it never used to do).

Has anyone else seen LED bulbs behave like this? New to me.



Yes.

Seen all sorts of **** with them. But that is one I have seen.

There is a technical term for it....


--
Adam

Curious bulb behaviour
 

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

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"ARW" wrote in message
...
On 06/05/2020 20:50, Tim+ wrote:

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.



Yes.

Seen all sorts of **** with them. But that is one I have seen.

There is a technical term for it....


--
Adam

Curious bulb behaviour
 

Tim+ wrote:

Additionally when switched off it €œfades
our€� over a second or so

most of mine do that, but they didn't just start doing it one day.

Curious bulb behaviour
 

Brian Gaff (Sofa 2) wrote:
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


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

Curious bulb behaviour
 

Paul wrote:
Brian Gaff (Sofa 2) wrote:
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


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

--
Please don't feed the trolls

Curious bulb behaviour
 

On 06/05/2020 21:24, ARW wrote:
On 06/05/2020 20:50, Tim+ wrote:

A LED pendant light with a supermarket own brand 9W bulb is running
considerably dimmer than normal.Â* Additionally when switched off it
€œfades
our€� over a second or so (which it never used to do).

Has anyone else seen LED bulbs behave like this?Â* New to me.

Yes.

Seen all sorts of **** with them. But that is one I have seen.

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.

There is a technical term for it....

Modern LEDs are so efficient that they sometimes glow when "off" just
from the capacitive leakage current from the mains wiring.

--
Regards,
Martin Brown

Curious bulb behaviour
 

On Wednesday, 6 May 2020 23:39:38 UTC+1, Paul wrote:

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.

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