Why do my fluorescent lights flicker and require cycling the switch to turn on?

Question

Bathroom has a 2 T-Fluorescent bulb fixture. The bulbs went out a 2-3 years ago I believe for the first time in 10+ years (when the fixture was installed). From the moment the bulb were installed, the lighting seemed peculiar. They have this extremely quick strobing effect so the light is not a solidly emitted. Fast forward to about a month ago and the bulbs had trouble turning on and the bulbs would stay dim at the ends or flicker a bit signifying that there is at least an electrical signal. One of the bulbs also has one black end if that means anything. Would need to flip the switch several times before the bulbs would fully light up, however once on they wouldn't go out.

So I did some research and I thought maybe the fixture and ballast is old and needs replacement. My dad says I just need to change the bulbs, but seeing as though I changed them quite recently (these bulbs are supposed to last tens of thousands of hours and we use them maybe an hour a day at most?), I didn't think that was likely. I thought at first perhaps I used t12 instead of t8 but just confirmed that the ballast states t12.

So now the bulbs won't light up unless we flick the switch several times. I don't really know anything about lighting at all, but I think the key fact is that the bulbs are STILL WORKING, and they both had problems at the same time, so I have to assume the bulbs are not dead, which is the most confusing part. Do fluorescents tend to malfunction rather than straight out die at the end of their life?

Can someone with expertise give their best opinion as to what's going on? Do these low-medium end fixtures tend to wear out after 15 years?

Thanks for your answers in advance.

Answer 1

One of the bulbs also has one black end if that means anything.

That means it is an old fluorescent tube approaching the end of its life. Generally the end gets darker and darker over time. This is an effect of the starting process eroding the filament at one end.

Do these low-medium end fixtures tend to wear out after 15 years?

No, they can keep going for much longer but some (many) will fail early and a few will last unexpectedly long.

Older installations used a starter that is worth replacing if you have problems.

I would test the tubes in another fitting that is working well (note: you can probably buy a cheap fitting for $10 and just use that for testing tubes)

Answer 2

I assume the fitting has 2 x 2' long tubes. In that case, the tubes will be in series, with one ballast designed for a single 4' tube. It seems like the starters are the problem. I would recommend replacing them with good electronic ones that fully preheat the filaments before allowing the tubes to start. Glow switch starters that allow the tube to blink on before the filaments are fully heated damage the filaments (cathodes). It is a process called sputtering, where the high voltage between the gas & insufficiently heated cathode causes the gas ions to slam into it, dislodging atoms, like sandblasting on an atomic scale. There is a well designed starter from an English manufacturer (I think the brand is Pulse starter) that fully preheats the cathodes. They come in a transparent green case and are available from electrical wholesalers. Get the ones designed for 2 x 18W tube fittings (where tubes are series connected). In our 1984 vintage range hood, the 1st tube lasted about 10 years. The second one with one of those starters is still going. The Thorn 2D compact fluoro fitting in our main living area, which I changed to a 4 pin tube and used one of those starters has been running every night since about 2010 with the same tube. The ends aren't even black. The tube is getting old and grey but it just won't die. I will eventually pension it off and replace it with an LED bulb when it gets too dull.

Answer 3

Having to flip the switcb repeatedly to start bulbs indicates not enough voltage is reaching the start circuit within the bulb. Frequently this is caused by tarnished terminals in the sockets causing excessive resistance in the circuit. Try rotating the bulbs back-and-forth in the sockets about ten times and see if that fixes it. I bet your first replacement bulbs were OK, but all the bulb-changing solved your problem for now. Thanks to my brother-in-law, Sandip Tiwari, for this tip, which I thought was absurd until I tried it...