Mystery LED flickering.

[Bootalito]

I've replaced all of my incandescent bulbs with LED bulbs (a few years ago) and they have been flickering randomly.  Now before you jump down my throat for not just googling it, let's assume I've googled, explored, and tested all possible reasons why LED bulbs flicker.  So without furthor ado here is the data:
1.  When the bulbs flicker, its a regular pulsing at about 60hz ("eye balling it"). 
2. All bulbs on the same circuit (as in powered from a single switch, maybe not an actual branch circuit) flicker in unison.  Also bulbs from different manufactures on the same circuit.  Although I haven't taken them apart to see if they use similar driver circuitry.
3. The flickering is extremely noticeable, like when it happens its obvious and distracting and guests go..."what was that"?
4.  The flickering happens for 5-20seconds
5.  The flickering is random.  I may not see a circuit flicker for days, then it will flicker twice in a hour.
6.  Some circuits constantly flicker when they are dimmed low.  This flicker is barely noticeable, but its there.
7. ifferent bulbs installed in different types of outlets with different types of dimmers.  For example.  Most of the bulbs I purchased were expensive Cree bulbs.  I've since then purchased some sylvania and GE dimmable bulbs.  All experience the same random regular flicker
8.  Most of my cuircuits are on phase chopping AC dimmers.  However I've purchased compatible dimmers mentioned on Crees website by part number with no improvement.  Circuits without dimmers also experience the issue
9. I built a 12V 50Amp RGB lighting system for my deck using water proof LED strips.  I used a high quality Dell server power supply with n channel mosfets.  Fully custom built, soldered, and programmed by yours truely.  Still experiences some slight flickering.
10. I have LED fluorescent replacement bulbs purchsed from AliExpress with in-built drivers (BTW I highly recommend Sunway Lighting store).  Still a flicker.
11.  My voltage is ~123V at 60.00hz everytime I've measured it.


I need to ask my neighbors if they have the same issue to see if its noise from the power line.  Our high voltage(750KV) comes down from the high tension wires about 1 mile away.  The 35KV line travels about half a mile from the sub station, then disappears underground for neighboorhood distribution.  In between the sub station and the penetration for underground there is a foundry that I just happen to know uses induction heating to smelt its metal.  I'm talking like...SERIOUS power draw.  Use google maps and search for Timet in Morgantown, PA.  You'll see the sub station just NW of their property with houses just south of their property.  Is is possible our neighboorhood could be experiencing some noise when they turn that thing on?
One of the things I want to try is when my family goes to bed monitor a circuit that is flickering and turn off one circuit at a time to see if a piece of equipment in my house on some circuit is causing the issue.

Any additional thoughts would be useful  Thanks!

[Jeroen3]

LED lighting is highly susceptible to any line disturbances since the slightest change in voltage has an immediate effect on luminosity.
With normal light bulbs this effect is delayed over many cycles.

To add to the effects are cheap AC LED bulbs that do not have smoothing and are always flickering down to 0 lumens for a brief moment at double mains frequency.

[Towger]

As per Jerone3.  Mine pulse several times after the laser printer prints a page.

[Gregg]

Expand your internet searches to include AC line harmonics and power quality. 
Your problem may be the foundry and you may be able to get the power company to address some of the problem if you can definitively point to the foundry as a major source of the problem.  On the other hand some of the (really cheap) LED power supplies may be the cause.

[capt bullshot]

Many years ago, we've had massive flickering (normal light bulbs) here. You could tell from the light flickering when the nearby (about 5km away) arc furnace plant started their melting process of a load of scrap metal. It kept flickering as long as the arc furnace was active. Then you had a few hours of steady light when they did loading / unloading of the furnace.
It's totally gone now, though the plant is still alive and kicking. Reason is: They got their own substation supply from the high voltage (don't know 220kV or 400kV) network. Before that, they were on a lower level of the distribution network.

BTW
There are meters called "Flicker Meter" that do a weighted analysis of line voltage fluctuation, resulting in a value proportional to the humans eye flickering impression of a standard 60W light bulb. From their recordings, you could easily tell the shifts of the arc furnace plant. These meters were calibrated to incandescent bulbs, LED bulbs can be more or less sensitive to fluctuations.
https://en.wikipedia.org/wiki/Power-line_flicker


I wouldn't expect flickering from a 12V lighting system induced by line voltage fluctuations, given it uses a regulated DC supply as you said.

[Mr. Scram]

My first thought was a welder being used or something similar. I guess a furnace fits the bill nicely.

[maukka]

I get the same flickering when I'm using a cheap heat gun.