Yesterday during a storm, my reading lamp flickered a bit (not unusual during a storm). Then it started making fizzy noises, emitted sparks, and finished off with a few puffs of smoke. The tube now has a small, burnt-looking hole and appears to have cracked, and the base was far too hot to touch.
Reading the 'warranty' for the bulb rather surprised me - "In certain circumstances at the end of its life,a CFL may emit smoke and a melting, plastic-like odor. This is a common occurrence in all brands of CFLs and is not considered dangerous."
Is this truly a _common_ occurrence? I've been using CFLs for years, and have never seen one die like this before.
No not in my experience. I did have an el cheapo b/Q one actually lose its tube completely once. Found it on the carpet, but they swapped it for a new one as it was only about 3 months old. They reckon it had used the wrong glue to hold it in. You just can't trust these Chinese makers can you.. grin. What worried me was that ok the glue gave way,but surely the tube was held in by solder or a socket for the wire ends? Brian
It's not common in the ones we get in the UK. (Seems to be much more common in ones bought in the US.)
Glass melting or cracking around the electrodes is caused by control gear which has carried on running the tube after it's worn out. When the emission material has all been sputtered off an electrode (leaving dark marks at the tube ends), the control gear should shut down the tube. If it carries on running it (which requires much more power), the remaining bits of electrode will run in "cold cathode" mode, which ironically means they'll get very hot, and melt or crack the nearby glass, and possibly melt any nearby plastic. (With a linear tube, it can result in the tube falling out of the fitting.) The control gear may not be able to supply the excess power without over heating and burning out itself.
Ideally, the control gear should detect a worn out tube, and stop trying to run it. IME, most CFLs you buy in the UK do this properly.
Yes, I noted that many of the cheaper torches which used invertors seemed to carry on using the tubes after the black had got quite bad. This must surely be inefficient. However many conventional old type fittings seem to persist in attempting to start tubes that are knackered as well with the familiar flash, stay on for a bit then go out and flash again, all the time wearing out the starter bulb of course and heating stuff up and wasting power. So how does one actually detect this? The lights on an old CCTV I had said they were used in cold cathode mode, which surprised me.
A lot of cheap tourch inverter circuits drive tubes really badly, which causes premature sputtering anyway. It's only when the last bit of emission material is sputtered off a filament electrode that the tube is worn out, as it only needs a bit to work.
Switchstart - they fail to stay on after striking because there's not enough voltage headroom on mains voltage to operate the tube in cold cathode mode. Any modern well designed control gear will quickly give up trying to light a worn out tube. You can get electronic starter replacements which will only try to start the tube for a second or so before deciding it's dead.
Modern control gear detects this in several ways: Burned out filament electrode (happens when it overheats due to running in cold cathode mode); Tube operating voltage going too high (although that's difficult if the ballast has been designed to operate a wide range of tube lengths with different operating voltages); Tube starting to rectify (as one end always fails first, so electrical conduction in each direction becomes asymetrical).
Some will even notice if you replace a tube live (by the filament electrode contacts remaking), and then retry starting the tube.
Properly designed cold cathode tubes have a much longer life than traditional (thermionic emission) tubes, long enough to last the expected life of the equipment without replacement. If they can be made long and thin, their efficiency isn't too bad either, and they are more easily dimmed. These are the reasons why they're used as backlights (although LEDs have taken over much of that nowadays).
We've had one explode once. We heard a screem coming from upstairs only to find shards of glass over my daughter's bedroom floor. However she then reported that the bulb had been "flickering" and "making a funny noise" for some time before the incident.
We've also had some that had started smelling but had no visual sign of damage.
Many years ago I experienced a CFL that after fitting lasted about one mains cycle before doing that. Huge ear shattering bang on power up and the external temperature of the base got way above the point of contemplating holding it.
Can't fault the distributor (Farnell) as they were very proactive in withdrawing them from sale and giving an immediate refund not just on that lamp but the other ones purchased. Some days later their supplier contacted me for further information but they left the distinct impression they couldn't give a toss about it, hardly surprising as it was 'Ring'
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