Fluorescent Lights

[The Medway Handyman]

Hi All

Ws doing a few jobs in an office today and the customer asked me to change a few fluorescent tubes. Seemed simple enough. The fixtures had three tubes in each. In one office they told me two tubes had gone, they replaced them and they blew again.

At their request I changed two tubes and all three starters (which they supplied). They old starters seemed to be brittle as though they had been exposed to excess heat.

The tubes appeared to be wired in series? Is that right? When I switched on, the unchanged tube still worked fine, but the other two flicked on and off alternatively. You could see that one end of the tubes was getting hot, so I switched off & removed the two tubes I had changed.

In the office next door they had a three tube fitting with only two tubes installed. They had apparently removed the third tube because it flickered. One of the two remaining tubes had started to flicker. I changed two tubes and one starter and it works a treat.

Any idea what could be wrong? I have little experience of fluorescent lighting. I suggested they get a sparky to look at the first fitting.

[Andrew Gabriel]

Maybe, but also the UV from the tubes can cause this.

It is common to wire two 2' 18W tubes in series, but you need starters designed for series operation (actually, they are same as the starters used for 120V mains). In your 3-lamp fittings, you'll probably find one series pair and one standalone, and the series pair will require different starters from the standalone.

How could you see that?

Wrong starters possibly. Do the fittings have loose end-caps which could have been cross routed to the wrong tube-ends?

[meow2222]

I think your questions been answered now, most likely a starter problem. The usual drill is to replace just the starters first, and if it still wont run then replace the tubes. Tubes in series means you need series starters, using ordinary ones may not work.

But you wont find 3 tubes in series, as already said.

Quite likely some of the tubes you took out are fine.

NT

[The Medway Handyman]

These were 4' tubes, not sure of the wattage.

One end looked red and felt hot.

No, the end caps were firmly fixed in place and all the wires tied in.

[Andrew Gabriel]

You can't run 4' tubes in series on a simple series ballast -- there's not enough headroom between the sum of the tube voltages and mains voltage. Some electronic ballasts do run multiple tubes in series, but they don't use starters.

Both ends should get exactly same heating. If one end glows red and the other end white, then the red end of the tube has run out of emission coating on the filament (usually ends up coated around the tube end as black marks), and tube is dead.

I can't imagine what type of setup you are looking at, sorry.

[meow2222]

The 2 end filaments are in in series during start on glow start fittings. They will always get the same power, and thus glow the same colour. (Thermionic emission does not affect colour) If the tube ends are glowing different colours, something's wrong, maybe a wiring fault.

With 4' tubes check youre not using: a 4-20w statrer a 100-125w starter a series starter

NT

[The Medway Handyman]

I think the starters had 4 - 80 printed on them. I'll call the customer & confirm that. I think they bought a box of starters from their office supply company, so they could well be the wrong type.

Thanks for your help.

[meow2222]

they sound ok... if a new tube and new starter dont fix it then either the new bits are faulty or the fitting has gone wrong somewhere. I get the feeling you wont be offering fitting repairs.

NT

[The Medway Handyman]

Dead right! I only changed them as a favour!

I'd like to learn a bit more about fluorescent lights. Is there a web site with any info that would help?

[Guy King]

The message from "The Medway Handyman" contains these words:

I'm sure someone will tell me that Wikipedia is crap[1] - but this has quite a lot of info

And if they do they can go edit it.

[meow2222]

classic mistake :) When they ask that its because they darent ask anyone to take it on as a real job.

NT

[meow2222]

actually there are problems with that article. The info Dave needs isnt there, and a large amount that isnt needed is. The descriptions apply to North American lighting, which is not the same as ours. The occasional error doesnt matter as most of it isnt really relevant to choosing, fitting or fixing fl lights.

What you need to know comes down to a few things, presumably each of which can be googled:

- circuit diagram of glow start fluorescent fitting (almost all british lights are glowstart, with some being electronic. The various other types used in NA are rarely found here.)

- how goddamn horrid cool white tubes are

- repair sequence, covered in previous reply

- the different glow starters, theyre not all compatible

- the fact that with the right type of circuitry, tube and installation they can look every bit as good as filament lighting, but regrettably most fl installs are crude and ugly.

- which tubes to choose and which to avoid, different for all fl versus mixed lighting.

- the once semi-popular idea that fl lights should be left on when not needed is a myth

I wrote a piece in the 90s explaining the different tube types and how to do good installations, but I doubt I could find it. Google for trough and shelf fittings.

NT