On Thu, 20 Dec 2018 03:54:10 -0000, Clare Snyder wrote:

On Wed, 19 Dec 2018 11:23:00 -0000, "William Gothberg" "William
wrote:

Do switch mode power supplies flicker in time with mains? Specifically LED power supplies in commercially available domestic lamps. 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? And is there any way I can test this? 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.
Leds (at least white ones) on a switch mode supply will not flicker
because the persistance of the phosphor is longer than the period of
the switching frequency which is more than 100kHz - typically 2 mhz.
The answer to the second part of the question is no, the switching is
not syncronized to the mains frequency on MOST switch mode power
supplies.

I'm definitely getting 100Hz flicker from it, I timed it using a slow camera shot (1/10th of a second) while moving the LED across the camera's field of vision. There were exactly 10 bright spots, although they were only 8% brighter than the dim spots. The LEDs don't go off completely. It's enough of a flicker for me to see with my eyes if I scan past the light, and I can detect anomalies when watching something rotating, like a drill chuck. I've got an oscilloscope on order, then I'll be able to check the signal to the LEDs (and in other parts of the supply) accurately.