Re: LED Lighting?

["Bill Taylor" <groups@xxxxxxxxxxxxxxxxxxxx>]

It's likely to be true. Low power indicators could well be fed DC via
a current dropping resistor, but anything more powerful is likely to be fed
from a switched supply.

If you want to dim LEDs the best way is fast switching with variable
mark-space ratio, so any dimmable LEDs will use switched DC.

Mains replacement LEDs will be fed from rectified AC so will be pulsed at
50 or 100Hz.

The actual frequencies used will vary, but most of them use very low
frequencies; you can see the flicker.

Theoretically squarewaves have a very wide spectrum, but the RF output from
a few kHz square wave is very low anyway and any design that emits
significant intereference will be spectacularly bad.

--- In ukha_d@xxxxxxx, "Tracey Gardner"
<tracey.gardner@...> wrote:
>
>
> A remark on LED lighting was made on another list that I am a member
of.
>
> The remark was as follows,
>
> "One thinks of LEDs as being innocent DC devices fed via a
resistor. But
> modern designs often turn them on and off at frequencies in the kHz
range,
> generating harmonics going into the lower radio bands"
>
> I also imagined that LED lighting was purely DC driven and I'd be
interested
> to know if this statement is correct?
> If it is correct does anybody have any idea of the frequencies
invloved?
>
> Thanks
>
> Tracey
>




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