(Peter Ashby) wrote in news:1i012q3.1a0ekg314xrqxdN%
:

Baron wrote:

Peter Ashby inscribed thus:

.....
Well practically you would be ill advised to use a generator as an
electrical motor but there is in essence no functional difference
between the two. So with a LED a current leads to light being
emitted, there is no theoretical reason why if I shine a strong
enough light of the right wavelength on a LED I won't get a current
out of it. In practical terms if I want to use my LED in this way I
will get more efficent performance if I optimise it for this
function. But this does not change the underlying reversibility of
the physics.

Peter

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Actually I have practical experience of this phenomena !

I used an LED as a noise source, and it worked very well, but had real
problems suppressing the 50 Hz hum on the signal, until I realised
that the hum amplitude changed when I stood between it and the
fluorescent light !


Cool!

Did you rule out that you were blocking a magnetic signal?

People are not very good at acting as a magnetic shield. You need a good
conductor for an AC field and Mu Metal to block DC magnetic fields.
[or a super conductor]

My ham tranciever was sensitive to AC magnetic fields. The VCO oscillator
coil, a toroid, picked up the AC magnetic field from the tranformer in the
power supply. This made a noticable hum modulation on received and
transmitted signals. The manufacturing company has a mod kit available that
replaces the toroid with a smaller toroid that is shielded.

While I was trouble shooting the problem, I found that my soldering station,
which has a tranformer in the base, would also modulate signals.
Moving my hand in between the radio and the transformer did NOT change the
signal significantly. Therefore I doubt that the source of the ac that he was
seeing was a magnetic field. Perhaps electrostatic, but I am betting that he
found that putting a piece of black paper around the led fixed his problem.

-bz-





--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

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