On Sun, 06 Oct 2019 00:08:39 +0100, AlexK wrote:



"Commander Kinsey" wrote in message
news
On Sat, 05 Oct 2019 22:18:44 +0100, AlexK wrote:



"Commander Kinsey" wrote in message
news On Sat, 05 Oct 2019 21:22:03 +0100, AlexK wrote:



"Commander Kinsey" wrote in message
news On Fri, 04 Oct 2019 23:49:23 +0100, AlexK wrote:



"Commander Kinsey" wrote in message
news On Fri, 04 Oct 2019 19:56:29 +0100, AlexK wrote:



"Commander Kinsey" wrote in message
news On Fri, 04 Oct 2019 09:41:25 +0100, PeterC

wrote:

On Thu, 3 Oct 2019 19:29:42 +0100, Robert wrote:

On 03/10/2019 14:29, Commander Kinsey wrote:
Why do LEDs generate heat? I want a technical answer not
"because
they're inefficient". And will we ever make them more
efficient?
Besides the inefficiencies in the LED itself which other posters
have
covered, LED lamps have some current regulation or power supply
built-in
which will not be 100% efficient and thus generates heat.

If my meter is correct, all the LEDs that I've measured have a PF
of
approx.
0.5 - not a good start.
One TV has a PF of 0.97 and is barely warm over the PSU; another
is
0.86
and
is luke warm. The real warmth in the 2nd. one is around the
inputs
though -
SPDIF, USB and HDMI.

I just tested one of mine with a meter, and it gave a power factor
of
1.00, at 256V, 9.8W. Yes I know that's an absurdly high voltage,
but
I
live opposite the substation so it's higher than the rest of the
street,
and they won't do anything about it. I consequently run my
computer,
lights, etc off a UPS, which automatically chops 10 or 20V off
when
needed.
It's the cool white, 9W version of this (not necessarily from this
seller,
but they look identical): http://www.ebay.co.uk/itm/262915986742
They contain a pretty decent looking switched mode PSU, unlike
some
other
bulbs I've seen which have a very simple capacitor dropper.
If any health and softy people want to be annoyed, then be aware
that
I
don't earth them. A couple of them made a humming noise when I
did.
If
I
touch the metal casing of an unearthed unit, and rub my finger
along
it,
I
feel a slight vibration. I guess something is jumping across by
induction.

More likely the capacitance effect you get with double insulated
stuff.

Could be. Would that also cause the buzzing when earthed?

That's more likely to be due to a significant earth current when
earthed.
Easy to measure.

0.020mA per foot of lighting (they're 4.5W per foot). I don't call
that
significant and can't see how it would cause an audible vibration.

Yeah, its more likely to be caused by something else.

Maybe its just not got the internal high frequency transformer potted
or mounted properly and you get resonance effect with the frequency
changing a little when its earthed so that you get the resonance effect
at that slightly different frequency.

I can't remember what the frequency I heard was, but it wasn't that
high,
probably something like 1 kHz. Aren't the transformers way higher than
that?

Yes, but the noise frequency is determined by the mechanical
resonant frequency of the mechanical stuff, not the frequency
of the current thru the transformer. In other words it can be
way lower than the frequency of the current. A sub harmonic in fact.

Ah, that makes sense. So I guess I could also fix it by simply sticking a
small weight on the device, like a lump of blutack, which would lower
the resonant frequency of the casing. But is it the casing that's
vibrating?

If that's the problem, even just jamming something like a toothpick
or bit of cardboard etc in the loose bit or even some superglue there.

Can't be bothered finding it, I don't believe in earthing anyway.