Sometimes it's the language engineers use to give names to things they work with regularly that takes a bit of getting used to.
I'll try and explain some of this in a way I hope anyone interested can understand.
The main thing with LEDs is that we have to limit the current they take, or they go pop.
Older, not very bright LEDs, have the current limited by what engineers call "Linear" circuits, such as a simple series resistor.
With linear circuits, the current stays steady all the time. A steady current does not produce any radio frequency interference (RFI) .
New, brighter LEDs need more current.
A linear circuit, like a resistor, would still work fine to limit the current, however it would have to be physically much bigger to handle the extra amps and it would get very hot.
Instead they use a "switching" circuit, which is far more efficient.
An electronic switch turns on the current, let's it build up, then before it get's too high, switches if off again.
After a short pause it turns back on again, then off, on, off, on, off, on, off ...
All this on-off-on-off switching is very fast, many thousands of times every second, so the human eye is not aware that anything is happening.
Have you ever thrown a power switch on an appliance or lighting circuit and noticed that occasionally this causes a flicker on the tv screen or a click on the radio ?
Throwing the switch changes the current. The more rapid the change in current, the greater the RFI it produces.
Imagaine now how much potential there is for RFI from an LED lamp that is internally switching on and off thousands of times every second.
Cheap and/or poorley designed LED circuits can generate an awful lot of RFI.
Better designed circuits limit the abruptness at which the switching takes place and so get rid of most the RFI.
