LED "Fluorescent" Light Blinking Occasionally on Start-up

Maybe a bad connection.

https://ledstore.pro/blog/2023/02/06/how-to-fix-a-flickering-led-strip/#:~:text=The%20primary%20cause%20of%20flicker,risk%20of%20a%20bad%20joint.

It's not that, I've check and things are tight. It only does it once and a while and if you turn it off and right back on it will be fine...

Without being able to look at the LED manufacturer's schematic for the power supply, it's hard to know for sure, but most LED power supplies take on the form of a regulated current source using a switch-mode topology of some sort. It sounds like that one particular unit may have a marginally stable control loop. Not sure of the reason for its instability, but a component value may be out of tolerance, an incorrect part may have been installed, or a part may have a bad solder joint and that part is "missing" from the circuit. And like you said, this instability is only initiated if you switch it on under just the right condition.

If you had a solid state relay with zero-crossing switching, it would be interesting to see if you used that device to power on this particular unit, could you get it to go all John Travolta on you with higher probability?

Is this a "Type A" lamp? That is the type used as a direct replacement for fluorescent tubes, without modifying the fixture. "Type B," also known as ballast bypass lamps, are made to be wired directly to the AC power line, for these, the ballast is removed from the circuit.

I've had problems with Type A lamps. They will work well in one luminaire, but in the next one with the same make and model of ballast, they may be very dim, strobe madly, either constantly or intermittently, or not light up at all. I suspect that the LED lamps are operating near the minimum current limit for the ballast. If there is insufficient lamp current, the lamp fault detection circuit kicks in. It may retry and shut off in an attempt to "light off" the tube - this causes the flashing. It may decide the lamp has failed and limit or shut down the driver, which produces dim or no light. The fault detection level evidently varies somewhat from one ballast to the next.

My fix is to use Type B lamps; it isn't that hard to remove the ballast and wire the lamp connectors to the AC input if you know how to do it safely. Note: you can get Type A/B lamps, which will work either way. I still prefer to save the energy that would run the ballast circuitry. If a Type B lamp flashes off and on, it's most likely defective, or the lamp connectors are severely tarnished.

If you are applying direct 120v to the proper type leds make sure that the tombstone socket pins are not tied together on one end,which is typical of most modern rapid start ballasts.The older,starter type ballasts were isolated on on end.These fittings can be ordered or you can dissect the socket and break the connection and reassemble.It may not be possible on some sockets

The reason is in the 120v leds.the ac lines runs the full length of the string of leds.

A jumper at the end will short out the printed strip and vaporize it.

Where to continue...

First of all, it is a replacement for a standard fluorescent bulb so no fancy power supply or wiring. You remove the old starter (yes, we are old fashioned over here and most fluorescent bulbs have starters (I live in Finland so voltage is 240v) ) and replace it with a "starter" but it is really only a 0,5 A fuse. I have replaced most of the old fluorescents with LEDs but this is the only one that is doing this.

I looked at the wiring for the fixture and there isn't a transformer...but there is some sort of choke or something wired into one of the legs, I tried to attached a picture of it, but it wasn't cooperating.

I do not know the specifics of the 220v fluorescent tubes,but the 120v tubes with starter had the isolated pins and must be removed to prevent shorting out the led string.All of the LED's are in series,and the power side is continuous from end to end.This way it doesn't matter which direction you insert the bulb.

The rapid start more modern ones had jumpered pins,so you had to change the sockets for them to work properly with LED replacements.

When upgrading from starter type old style to the newer rapid start type,the starter had to be removed and the starter socket pins shorted, and soldered together

The starter type fluorescent tubes were notorious for bad connections at the starter sockets,(usually black oxidation on pins and sockets)so that may be the case with your LED's.Clean the starter(in your case,fuse) sockets with a contact cleaner and see if that helps.A little spray of WD 40* after cleaning will help ensure a better connection.Matter of fact, would use WD 40* on all of my pins on the light.

Good luck.

*I get no endorsement from WD40, or it's parent companie(s,)and am not affiliated in any way.I am simply stating my opinion from 50+ years experience.

How old is the switch?

The notion that it is an occasional problem that can be solved by cycling the switch, makes me suspect that the switch is getting weak.

I remembered my former boss when we had a malfunctioning piece of equipment:

"Good gosh, boy! Don't troubleshoot it, just replace the damned thing."

To which I replied, "But I'm an engineer! I have to find out what's wrong."

Of course, the boss is always followed in the end but, yeah, we engineering types have this insatiable desire to know.

I'm an electronic tech, not electrical, but those LED-fluorescent tubes are also electronic devices...that I haven't studied. But this reminds me of a device, called an Infusomat (a medical device for injecting a constant flow of dextrose—and meds—into patients).

When switched on, it would sometimes start and sometimes won't. A few minutes of troubleshooting revealed a missing capacitor that was wired to the reset pin of the microprocessor (a Z80; those of you who are familiar with that processor will know that this is a very old story). Basically, when you turn it on, the power up reset is absent and start up is dependent on whether there is residual voltage in the power supply capacitors.

So, I would guess that you have a defective capacitor somewhere in your circuit. Granted, it most likely doesn't have a microprocessor but there's probably a capacitor in there that is supposed to set things in the right state for a power-on sequence.

regards,

Vulcan

What kind of LED replacement is it.Does it use the existing flourescent ballast or does it simply use the tube sockets?They come both ways.If it is the first type,it could be the old ballast causing the flicker.If the latter,it could be the internal led ballast.Swap the tube to a different location and see if the problem follows the tube or not.

HiTek, it simply uses the sockets...the starter (old style) is replaced with a 0,5a fuse.

It started doing it a LOT recently but cycling the switch always fixed it...so I started making an effort to slowly and forcefully switching it on and (knock on wood) it seems that it hasn't "disco'd out" on me lately so maybe it WAS a bad (or going bad) switch.

Thanks for all the replies and suggestions. As usual, the place to go for good solid advice on "real" subjects.