On Thu, 20 Dec 2018 08:19:58 -0000, gregz wrote:

Clare Snyder wrote:
On Wed, 19 Dec 2018 19:34:57 -0000, "William Gothberg" "William
wrote:

On Wed, 19 Dec 2018 18:03:19 -0000, 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?

Haven't got one unfortunately.

Since this landed in alt.home.repair, I gotta ask. Do you have
single-phase or two-phase?

Single. I'm in the UK.
so 50 Htz - you can almost see an incandescent flicker at that
frequency (at 25 you could)

(also rules out the previously mentioned "engineer friend")

Lights flicker at twice the frequency, once for positive cycle, and once
for negative cycle. LEDs only once unles using a bridge rectifier, or
steady on using DC. Even though blinking they look normal straight on, my
brain says something is wrong

Some brains (or eyes) seem to be faster than others. I can easily (and annoyingly) see flicker on CRT monitors below 90Hz, others don't even see the 50 or 60Hz ones. I can see flicker on 80% of car LED lights, others don't see any. Designers really ought to account for those of us with better eyesight.