Strange CFL Failure Mode

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This is a ~1 mm hole in the glass near one of the filaments. Something got hot enough for the glass to melt, and after that, as they say, the rest was history. :)

I've seen this on 3 CFLs in 3 different lamps/fixtures. There are no known problems that could account for such nasty behavior. They were all high mileage, so perhaps the filament at that end of the lamp opened resulting in the discharge going to one post, near the glass, or something. :)

The CFLs were all from GE but I don't know if they are of the same ballast/lamp design.

Comments welcome.

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Reply to
Samuel M. Goldwasser
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Sounds like a hot blob of tungsten or emission material was ejected from the lamp's cathode. An arc could certainly do that. It's common in incandescent filament lamps that arc upon failure; but I wouldn't have thought that there's enough energy available in a low-wattage CFL to do it. What were the wattages of the lamps?

But, there were some arcing problems with T5 and some T8 lamps a few years ago when operated on instant-start ballasts. At end-of-life, the cathodes failed and an arc started chewing away at the cathode mount wires. Things got hot, lamps cracked and lamp holders were charred. This all resulted in the development of ballasts that shut the lamp off if an arc was sensed so as to avoid the mess of cleaning up broken lamps and the concern that sputtering lamps, smoke and the smell of overheated plastic caused.

Terry McGowan

Reply to
TKM

Caused by control gear which fails to detect when the tube has reached end of life (emission material all sputtered off), and and provides enough voltage headroom to continue driving the tube as a cold cathode tube, which generates too much heat at the tube electrodes. Dead thermionic tubes don't last long when driven as cold cathode tubes, because the filaments and support wires are quickly burned away, until the tube cracks and vents to the atmosphere. If the support wires are very close to the glass tube wall, as is likely with thin tubes, it can melt the glass. With linear tubes, it can cause the tube to break such that it drops out of the fitting - I've had one case of this. This was in a set of T4 tubes which come in various lengths from 6W to 24W, and all use the same control gear. I had mostly 16W ones, and when the tube reaches end of life, the control gear simply up's the tube voltage to maintain the current, and the excess power is dumped into the (now) cold cathode electrodes, which start glowing as bright red hot dots, clearly visible through the dark sputtered coating which is now round the tube ends. The heat also did enough damage to the plastic lampholder that it was no longer usable. I did think this could be a fire risk too, particularly if there had been any flammable material nearby. (I've since been phasing these lamps out of use, which is now forced as the manufacturer has gone and no spare tubes available.)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Reply to
Andrew Gabriel

Plasma arc.

Reply to
Meat Plow

Hmmm. Another 'dangerous' aspect of these dreadful devices then. If they don't send you blind, or provoke epileptic fits, they'll get you by venting their mercury vapour !! :-)

Arfa

Reply to
Arfa Daily

. snipped-for-privacy@repairfaq.org...

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Yep, soon they'll be considered as dangerous as incandescent lamps that burn fingers, start fires, explode, send molten glass and tungsten shooting about and electrocute those who try to change the bulb. ;-)

Terry

Reply to
Terry

Yep, soon they'll be considered as dangerous as incandescent lamps that burn fingers, start fires, explode, send molten glass and tungsten shooting about and electrocute those who try to change the bulb. ;-)

Terry

My my, Terry. You do live an interesting and dangerous life ... During my many years of shuffling around on this little orb of ours, I don't think I have ever had a domestic incandescent light bulb start a fire, explode, reach a temperature where the glss could become molten, shoot molten tungsten at me, or try to electrocute me (how does that one work then ??). I would have to admit to having scorched (rather than burnt) my fingers a time or two, but that was down to me employing stupid tactics for handling them ... d:-)

Arfa

Reply to
Arfa Daily

No fires here yet.

I just had one infantile failure out of a batch of 6 I bought.

9 watts at 40 watts effective halogen brightness. I don't think being outside was a problem even thought its not for outside. These are flood or spots. What I have found, I can get moe light out of a 1.5 watt LED spot vs a 9-12 watt CFL. The reason being, CFL's are poor choice for spots due to the poor beam width.

A lot of CFL's say, no dimmers or relays. The same for LED's most of the time. I can't really figure the relay bit.

greg

Reply to
GregS

Hi!

I've seen the effect on some very narrow GE tubes in use with conventional overhead fixtures. When the tubes die, they oftentimes crack a ring in the glass or blow a slightly larger hole in it at either edge. This makes changing them "fun".

I'm not sure if it is specific to the tubes or not. The GE tubes have not proven long lived. I started dating them after some tubes from a different maker with the wrong color temperature were purchased and installed during late 2005. All of the misordered tubes are still going strong, nine hours a day in most locations. The oldest GE tubes date from 2007, and there are very few left. All fixtures are identical.

William

Reply to
William R. Walsh

Likely "solid state" relays. Some X-10 devices, for example, are solid state and may not work. A mechanical relay would work fine.

--
bud--
Reply to
bud--

That would explain it. Seriously, I find GE CFLs to be about the least reliable of any available, and their SOX and SON lamps aren't much better. Their mercury lamps seemed to be ok, but they are rapidly becoming extinct these days. I haven't had much experience with their metal halides.

Reply to
Stephen Furley

All that stuff has happened usually because (full disclosure) I treated the lamp rather badly. A drop or two of water on a hot 100 watt GLS lamp, for example, is sure to cause damage and, probably, fireworks.

I was electrically shocked when I tried to put a 60-watt lamp into a portable lamp socket with the socket turned on and didn't realize it was an old portable which didn't have a polarized plug. It's easy to touch the threaded part of the base when you reach under the shade with the lamp and try to position it in the socket.

Terry McGowan

Reply to
TKM

Ah ! That all makes more sense now. That last 'problem' can't occur in the UK as the outer part of the bayonet type bulb holders we normally use here, is not part of the electrical connection to the bulb, and is either sheilded with a bakelite type material anyway, or grounded if not. That said, we are starting to see more lamps with standard ES holders - allbeit shielded - and a lot more with MES holders that would be quite hard to stick your finger into to make contact with the centre pin. The wall plugs are not reversible like some U.S. ones are, but that of course doesn't stop people putting re-wirable ones on, backwards ... :-\\

Arfa

Reply to
Arfa Daily

This commentary reminded me of a quite-unpleasant experience in late boyhood. Apparently, an incandescent bulb in the cellar had a film of moisture on it (it had just been turned on). When I touched the glass, I got a nasty shock; damp concrete floor, etc. The socket must have been wired with its threaded shell to the hot side of the line.

Not the bulb's fault, of course.

Btw, hot glass is conductive, just about certain.

Regards,

--
Nicabod =+= Waltham, Mass.
Reply to
Nicholas Bodley

Well, if it is, and I rather suspect it's not, the amount of conductivity is very small. I work a lot with power valves (tubes) which run hot enough to take your fingerprints off in decimals of a second, and these often have as much as 800 volts on the anode pins. Some years back, I used to work with high power audio distribution amplifiers on a community radio network. The (foot high internally assembled with nuts and bolts) tubes on these 7 foot tall amplifier cabinets, often used to run so hot that the glass was actually glowing dull red. I have seen dents in the glass where the vacuum has started sucking on areas that have got *so* hot that they have softened. The HT supply on these beasts was about 2.5Kv as I recall, derived from mercury vapour rectifier tubes.

Given these facts, if the glass had much conductivity when hot, you would pretty soon be into having leakage paths between the pins, and to the grounded retainer metalwork, that holds the devices into their sockets, wouldn't you ?

Arfa

Reply to
Arfa Daily

Ordinary incandescent lamps are made from soda lime glass, which has enough conductivity at 100C to maintain a low frequency (DC or 60Hz) discharge in T12 fluorescent lamps using electrodes on the outside of the bulb. The place where the wires are sealed in an incandescent lamp (the pinch seal) is made from lead glass, that has much lower conductivity than soda lime glass. Vacuum tubes are usually made from borosilicate glass (Pyrex(R)) that has even lower conductivity than lead glass, and much lower than soda lime glass.

--
Vic Roberts
http://www.RobertsResearchInc.com
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Reply to
Victor Roberts

Thanks for that Vic. Always good to learn from someone 'in the know' on the more specialist aspects of electronics.

Arfa

Reply to
Arfa Daily

In , Arfa Daily wrote in part:

The glass around the pins is not as hot as the glass on the sides and the top.

Meanwhile, even soda lime glass is not that much of a conductor at

200-300 degrees C.

I have heard of HID lamps requiring any metal supports to be isolated, to avoid problems with electrolysis of the glass bulb. I imagine this problem involves amounts of current low enough to not be a shock hazard.

On the other hand, I have seen glass heated to the point of being soft conduct impressive amounts of current (several milliamps, possibly more) at a few kilovolts. I do not know what kind of glass was involved - either soda lime or a cheaper flint glass, probably soda lime.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

There's an interesting demonstration that can be done with a rod of soda lime glass. If it is connected to a source with the appropriate voltage output and current capability, and then heated, it will conduct enough current to sustain the temperature required for conduction when the external heating supply is removed. I'm sorry to say I don't know how much voltage is required to do this on any particular size rod of soda lime glass.

--
Vic Roberts
http://www.RobertsResearchInc.com
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Reply to
Victor Roberts

Any links to these giants?

-- Boris

Reply to
Boris Mohar

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