On Wed, 19 Dec 2018 11:51:35 -0000, Rod Speed wrote:

William Gothberg "William wrote

Do switch mode power supplies flicker in time with mains?

No.

Specifically LED power supplies in commercially available domestic lamps.

None of mine flicker at all.

By in time, I don't mean at the same 50/60Hz, but anchored to it. I.e. if
you have several such lamps each with their own built in supply, will they
all flicker in time, using the mains frequency to keep them in time, or
will they be random, making the room overall not flicker due to them all
being random?

None of mine flicker at all.

And is there any way I can test this?

Yes, Get or make a strobe disk or use
one of the original LP disks that has
a strobe disk on it and see what it looks
like with the lights illuminating it. You'll
get it appearing to freeze when rotating
if the light level is varying in synch with
the mains frequency.

I tried taking photos of them, but my camera only goes as fast as 1/2000th
of a second, which shows all the lights at the same brightness each time,
I suspect the flicker is above 2000Hz.

Or they don't flicker at all. No reason why a proper
switched mode power supply needs to have any
AC component at all on its output. The cruder
ones may well do.

They probably are fairly crude. I know they flicker, for example if I use my cordless drill, the chuck appears to spin the wrong way under the LED lighting.

But it's nothing like as low as 50Hz. What I want to know is if the higher frequency they're flickering at is anchored with the rise of the AC wave. I.e. will all the LED lights in the room flicker at precisely the same time, or will they be out of synch (due to tolerances in the circuitry of each PSU) and fudge the brightness together.