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light bulb explosion

Discussion in 'Electronic Basics' started by PatrickM, Oct 13, 2004.

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  1. PatrickM

    PatrickM Guest

    Sorry if it's the wrong newsgroup but I've came here before so I thought of
    asking here first...
    Today in our home kitchen a standard 100-watts light bulb "exploded". It
    happened just like that for no apparent reason, my girlfriend was in the
    kitchen reading and could have been injured by the flying glass from the
    bulb. The fuse didn't open. Has anyone ever seen or experienced something
    like that before? Why would that happen? Thank's for any info and sorry for
    my approximate english.

    Patrick, from Quebec, Canada.
     
  2. Eric Lambi

    Eric Lambi Guest

    Over the years I have seen several light bulbs explode with a sea of broken
    glass and sparks. I don't know why they went out in such a manner. One time
    was in a underground hallway leading to the University of Saskatchewan
    Library right in the middle of final exams! At the time I assumed it was
    because of too much angst.

    Regards,

    Eric
     
  3. Light bulbs ordinarily have a low internal pressure (much less than
    atmospheric pressure) so do not actually explode, even if the filament
    overheats for some reason (like a partial short circuit). But the
    glass can shatter from internal stresses (not properly annealed) or
    from being splashed with water.

    My parentheses keys are tired now. :p
     
  4. In my less sceptical days I recall reading that exploding light bulbs
    was a well known symptom of poltergeist activity. Were there also any
    books seen flying across the room? <g>

    As John said, bulbs should implode. But of course gravity then takes
    over and 'flying glass from the bulb' would be a natural description,
    especially from someone deeply immersed in a good book!
     
  5. Sometimes the glas part of the bulb explosion-like separates from the
    metal socket and flys off (in one pice, at least until it hits
    something).

    The second possibility is that the bulb imploded, that is the glass bulb
    itself cracked under the force of the (partial) vacuum inside. The
    fragments then move towards the centre of the bulb (in an explosion they
    would move away from the centre). However, as the fragments don't just
    stop at the centre, an implosion is operationally indistinguishable from
    an explosion.

    Both occasionally happes (often when the light is switched on or after a
    brown out), without any apparent reason and unpredictably. Just one of
    the risks of modern life, I guess.
     
  6. Richard

    Richard Guest

    Halogen lamps are particularly prone to this and can be quite
    dangerous. I once saw one explode on the Carson show. It started
    little fires everywhere the glass shards landed including the guests
    dress. Usually there was a scrim over those studio lamps for safety.
    This one must have been missing. I have seen them forming huge bubbles
    of quartz just prior to exploding.

    Richard
     
  7. Steve Evans

    Steve Evans Guest

    I can beat that. I was saw a sherry glass spontaneously fracture into
    a myriad of shards right before my eyes, for no apparent reason at
    all! I can understand the odd light bulb going 'pop' from time-to-time
    since it is, after all, hot, stressed and has a limited life
    expectancy. One expects a bit better from a simple drinking vessel,
    though...
     
  8. I stumbled across the explanation under a Britannica entry for Argon.

    Manufacturers put argon in light bulbs as an inert fill gas. Unfortunately
    argon has a low breakdown voltage, so if the filament burns out, an arc
    will leap across the broken ends. So, manufacturers put some nitrogen
    in the argon to raise the breakdown voltage.

    But sometimes an arc will strike across the broken filament ends.
    When this occurs, the normal "yellow" light bulb color will turn
    brilliant blue-white for a moment (until the filament is vaporized
    by the arc, and the arc quenches out.

    But sometimes the arc continues for too long. Or perhaps the
    manufacturers got the gas mixture wrong. The hot arc will cause
    the argon pressure in the bulb to skyrocket. The bulb will burst
    with a bang.

    (A similar thing occurs if you put a bulb in a microwave oven for
    a couple of minutes. The hot plasma inside the bulb will vaporise
    the filament parts, then cause the bulb to explode via overpressure.)
     
  9. Richard wrote:

    I'd guess so, their operating temperature is much higher than that of
    ordinary incandescent lamps. The screen btw helps not only against
    flying bits, but also screens the UV ratiation produced by the lamp
    (higher temperature -> more light of shorter wavelength)
     
  10. tlbs101

    tlbs101 Guest

    Back when I went to college I worked at a number of television
    studios. Occasionally I would have to replace the halogen lamps in
    the studio lights. They were typically rated 1000W and "ran" very
    hot. The bulbs were wrapped with special handling paper. If you
    accidentally touched the bulb with your bare fingers, the slight
    amount of oil from your skin would be enough to cause an instant
    explosion the first time the bulb was turned on (they "docked" your
    pay if that happened).

    I doubt that is what happened to your 100W bulb. Given that millions
    of bulbs are manufactured each day? week?, statistically some will
    have slight flaws that will cause this type of failure.

    Tom
     
  11. Richard

    Richard Guest

    Well that explains a lot! Sometimes when a bulb goes out you can get
    it to burn again by flicking it. Sometimes the filament will fuse back
    together and it will burn again.

    I have seen that brilliant blue-White arc sometimes when a bulb burns
    out. It can be quite brilliant and very violent.

    We also used to use dichoric glass in front of quartz lamps to change
    the color temperature.

    Richard

    Richard
     
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