On Thursday, December 20, 2018 at 7:51:32 AM UTC-5, William Gothberg wrote:
On Thu, 20 Dec 2018 04:31:31 -0000, Clare Snyder wrote:

On Wed, 19 Dec 2018 13:03:19 -0500, "Clark W. Griswold"
wrote:

On 12/19/2018 11:36 AM, William Gothberg wrote:
On Wed, 19 Dec 2018 16:18:29 -0000, Mark Lloyd wrote:

On 12/19/18 5:23 AM, William Gothberg 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.

I once had an audio amplifier with a solar cell rather than a microphone
for the input transducer. This made it possible to listen to light. The
sun is steady, incandescent lights (AC powered) hum.

That was 40 years ago. Maybe something like that would work today.

The trouble is I want to compare 2kHz+ from one light with 2kHz+ from a neighbouring light and see if they're in sync.

Maybe use a dual trace oscilloscope?

Since this landed in alt.home.repair, I gotta ask. Do you have single-phase or two-phase?
No such thing as "2 phase" -

Perhaps he meant split phase, like in the USA - centre tapped 240V. Which could conceivably mean I could have some lights on each circuit, and if they were fed by half wave rectification, flickering at 50Hz, they could be out of time with each other and make the whole room flicker at 100Hz, filling in each other's gaps. Mind you the same can happen by just putting the bulb in the other way (in the UK bayonet cap fittings allow you to connect live/neutral the other way at random with bulbs).

They won't be out of time with each other as each circuit is reaching it's
peak value at exactly the same time. That's how you get 240V, 120+120 = 240.