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Strange CFL Failure Mode

Discussion in 'Lighting' started by Samuel M. Goldwasser, Jul 15, 2009.

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  1. See:

    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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  2. TKM

    TKM Guest

    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
  3. 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.)
  4. GregS

    GregS Guest

    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.

  5. 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.

  6. bud--

    bud-- Guest

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

    TKM Guest

    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
  8. 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 ()
  9. Thanks, interesting.

    However note that Pyrex(R) no longer implies any particular
    glass type, and in particular, it's no longer borosilicate
    glass in the US.
  10. TKM

    TKM Guest

    Fascinating. I wonder if there are glass furnaces that switch from gas to
    electrical glass-conductive heating once the glass is molten.

    Terry McGowan

    Terry McGowan
  11. I do remember seeing somewhere on the Web how to melt a soda bottle (or
    was it a beer bottle?) in a microwave oven. The glass bottle to be melted
    required a hot spot pre-heated with a "blowtorch" / "propane torch" or the
    like, to temperature that I visually estimate to be in the 800's degrees C.
    It appears to me that soda lime glass that hot achieves conductivity and
    resistivity suitable for being sufficiently receptive for heating by a
    microwave oven.


    Disclaimer: I sense that this is adventurous usage of a microwave oven,
    attempt to do such only at your own risk of damaging your microwave oven or
    burning down the real estate that such microwave oven is in/on and
    injuring/killing life forms in/on such real estate including loved-ones,
    friends and pets by starting a fire.

    - Don Klipstein ()
  12. This makes me wonder if the name "Pyrex" "expanded" to glass types other
    than borosilicate, as opposed to merely being "expanded" to non-glass

    - Don Klipstein ()
  13. In the US, Pyrex is currently tempered sola lime glass:
    A factory in Europe also licenses the name, and apparently
    produces borosilicate glass.

    Pyrex is now simply used as a respected brand name, still
    owned by Corning, but licensed out to whoever wants to use the
    name. It doesn't imply glass, or any particular type of glass.
    Corning no longer make anything under the Pyrex name themselves.
  14. Franc Zabkar

    Franc Zabkar Guest

    I had a bad batch of incandescent light bulbs where the glass
    separated from the base and fell, or was ejected, onto the floor.

    - Franc Zabkar
  15. Jeff Jonas

    Jeff Jonas Guest

    Yep, soon they'll be considered as dangerous as incandescent lamps
    Please don't say that too loud, lest the electrician's union
    place a seal and/or lock on every fixture
    to assure only a licensed union electrician ever changes a lamp.
    Don't laugh. With all the microcontrollers embedded into everything,
    it's possible to add lockout codes so only authorized people may restart it,
    just like you car's "service required" light and reset code.

    It's bad enough my TV, monitor, radio and such all say
    "No user servicable parts inside".
    Pray, don't let that happen to my home too.
    I had a night light bulb shatter, fresh from the package.
    I'd say that counts as an explosion.
    I swore off dollar store bulbs ever since.

    As to fires, I refuse to use lamps over 100 watts at home,
    thus avoiding the 300-500 watt halogen torchiere fires
    that were terribly common for a while.
    The closest I came to a lamp induced fire was a plastic figurine
    melting and smoking from being too close to a reflector halogen lamp.
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