Fluorescent lamp noise

[kellymarie]

My shack/workshop is lit by a twin 36 watt flurescent fitting I've noticed that it causes bad interference when the tubes first strike it seems to be getting worse the older it gets. But I've noticed that the noise gets less and less as it warms up reducing to almost nothing after about 10 minutes although this is or at least appears to to temperature dependent. The reason I'm posting this is if anyone else has a noisy fitting don't despair it can improve as the tubes get warmed up

[Analogue man]

If you are talking about a buzz from the light fitting then it will be the ballast choke making the noise.

[Maarten]

I assume RF noise. I think this will also depend on the exact cathode construction and gas mixture. Some tubes will even show a kind of swirling light effect when very cold. I can imagine this will make even more noise.

Even incandescent light bulbs are capable of oscillating (which is known as the Barkhausen phenomenon), so in any case I'm not surprised.

I'm not sure if it's appropriate for the forum, but the attached image seems relevant.

[high_vacuum_house]

I wonder if the tube is getting near to the end of its life and one cathode is running out of emission. This will cause it to start acting like a rather poor rectifier causing DC current through the choke. This would cause some funny RF to be created. The tube itself could start acting as a noise diode!

Christopher Capener

[Craig Sawyers]

The perils of RF interference from lamps and RF reception is discussed here

https://www.chavfreezone.me.uk/2018/LED-Driver-QRM.html
https://www.chavfreezone.me.uk/2018/Linear-LED-Driver-PSU.html

Craig

[kellymarie]

I should have made it clear yes it's RF noise not physical noise stronger near the LF end of the mediumwave band. I don't think the tubes are near the end of life the ends are only slightly blackened I've heard before that tubes can self rectify I've seen it happen in large installations where maybe 1 or 2 tubes go bad in that way. Yes I've heard of Barkhausen noise I believe it's something that can effect horizontal output valves as well as ordinary light bulbs.

[The Philpott]

If it's a bother I'd spin some 600 grade paper round the brass pins, and possibly clean the springy contacts as well. The connectivity between G13 pin and spring leaf was never ideal from new, and the brass goes black with time.

Dave

[G6Tanuki]

Yes, try cleaning up the contacts; if that doesn't fix it them invest either in some new-old-stock tubes or do the job properly and go LED.

[seymour32]

Hi, I asume the fitting is what was years ago marketed as "High Frequency" fitting, (electronic ballasts). The ballast is designed to Strike the tube and them maintain the light output. As the tube ages the time taken becomes longer to get the tube up to "optimum" working conditions. I would suggest the tubes are coming to the end of there lives and either replace with branded tubes or have the fitting replaced with LED fitting. NOTE:-Theses fitting will NOT take standard LED Tubes conversion as the Ballast will need to be removed and the fitting internally rewired.

[David G4EBT]

I'd also be inclined to replace the tubes with LED ones, having just done that.

As said in the post above, if the fixture has an electronic ballast (no starter), you must bypass and remove the electronic ballast, as it would damage the LED tube. How to tell: With an electronic ballast there's no visible starter, and the ballast is typically a larger unit inside the fixture. If that's so, it requires rewiring the fixture to connect the main voltage directly to the lamp holders.

If the fixture has a magnetic ballast (with an externally visible 2-pin starter), you just need to use the replacement LED starter that comes with your LED tube. (The LED 'starter' is basically a dummy, with a internal link across the two pins). If that's the case, you simply remove the old fluorescent starter and fluorescent tube, then install the new LED starter and LED tube.

I have two 6ft twin-tube fluorescent batten fitments in my garage, and recently replaced the four T8 (1") 80-Watt tubes with four 6ft 24 Watt LED ones from Screwfix. I'm not sure how many lumens the old tubes were, but to my eyes, (20/20 vision after cataract surgery!), the LED ones look every bit as bright. They're neutral white and have a 5-year manufacturer's guarantee. 96 Watts total replacing 320 Watts, so a worthwhile saving in consumption over time.

Easy job - just twist the old tube 90 degrees so the pins are vertical and take the tube out. Push the new tube in with the pins vertical and, twist it through 90 degrees. Replace the old starter for each tube with the LED one, and switch on. Basically, a 5-minute job.

Screwfix stock LED replacement tubes from 2ft to 6ft. Current prices are 2ft, £4.49 each, 6ft ones £10.99 each:

https://www.screwfix.com/c/electrical-lighting/tube-lights/c...bulbtechnology=led&lightbulbtype=t8

There's a 17-min review of the tubes at this link, (if you can tolerate the intrusive youtube ads).

Some interesting comments about the light output versus the fluorescents:

https://www.google.com/search?q=do+LED+replaement+tubes+for+...d=cid:f9518382,vid:OyY6iJguBVE,st:0

Hope that's of interest and use.

[The Philpott]

Definitely of interest and of use, as we expect.
I think a T8 6" 'tube will be 70w, but that's nitpicking.
I've retained fluorescents in the interests of longevity and thus trading this off against consumption economy, but each to his own.

I'm not a fan of the HF ballasts as they don't seem to last as long. Worth noting that they flicker if mixed with 50Hz fittings operating on the same loom.

Dave

[Maarten]

Some LED tubes are especially meant to work on HF ballasts, so it's not a hard and fast rule that thse need to be removed.

[ex 2 Base]

I would change to an LED tube, but in my working day we did change noise chokes especial in offices.

[broadgage]

IME, radio interference from fluorescent lamps is generally worse with lamps near the end of life.
As the lamp wears, the lamp voltage increases, and the lamp has a "hard" turn on at the relevant point in the mains cycle. This tends to result in RFI.
A new lamp with a soft turn on produces less RFI.

ISTR an old thread about excessive RFI from a circular fluorescent magnifying lamp, I suggested a new lamp, which was reported to considerably improve matters.

[kellymarie]

I will keep the tubes going for a bit longer if I can I'll try cleaning the end brass pins that mite help and it definitely won't do any harm. As I said the noise does go away once the tubes are warmed up so it's not a major issue. They are magnetic ballasts not electronic the noise they make is definitely modulated at 50 or 100 cycles. I can see one of the starters as well just to prove the point. I'm reluctant to fit LED tubes as they can be noisy too and I don't want to give in to a technology forced on us by the green brigade!

[Maarten]

I'm curious whether removing the starter once it's started, makes any difference.

[Chrispy57]

Hi Maarten - just tried that for you, and the starter acts like an on/off switch!
1970s 5foot 80W flourescent light fitting with standard choke and starter, replaced tube with a 26W LED tube and fitted replacement LED type starter. Powers up and runs OK, then removing the starter causes it to switch off (lamp goes out), refit starter, lamp comes back on.
Cheers
Chris

[Maarten]

That's a spectacular result... Clearly there's some interaction then. Maybe the capacitor in the starter forms part of an oscillator, or the voltage over the cold tube is a bit higher and pushes the starter close to its ignition voltage.

[David G4EBT]

Originally Posted by Chrispy57

Hi Maarten - just tried that for you, and the starter acts like an on/off switch!
1970s 5foot 80W flourescent light fitting with standard choke and starter, replaced tube with a 26W LED tube and fitted replacement LED type starter. Powers up and runs OK, then removing the starter causes it to switch off (lamp goes out), refit starter, lamp comes back on.
Cheers
Chris

That's because the LED 'starter' isn't a 'starter' as such - its just a wire short across the two pins to complete the circuit.

If you remove the 'starter' you create an open circuit.

[Chrispy57]

Hi David - yes, I learned that from your Post #10, which was what encouraged me to buy a couple of LED tubes from ScrewFix over the weekend. The timing was perfect, since their Sale ended on Sunday, so I got a £10 tube for £7.68.

Cheers
Chris