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Turning lightbulbs on and off makes it blow faster False or true?

  1. Apr 10, 2007 #1
    When you were little you were always told not to "play" with light, by turning it on and off. This was because the light bulb would "blow up" faster..

    But is this true?

    I have learned that the tungsten filament in a light bulb wears up because of the heat that makes the tungsten "vaporize" slowly.. So I don't see how turning the light on and off would make it "blow up"/"burn over" faster...??

    explain please.. is this myth true or busted? :P
  2. jcsd
  3. Apr 10, 2007 #2

    but not the 'right' reason---

    turning the light 'on' causes a immediate surge that makes the filament vibrate/jump with the potential to break the more often it is 'turned on'
  4. Apr 10, 2007 #3


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    Except for the rather minor effect that rewebster mentioned, no. The idea that turning on an incandescent light "harms" it more than just having it on is an "old wives tale". It is, however, true that the ballast in neon lights are affected more by turning on the light than letting the light run.
  5. Apr 10, 2007 #4
    I also thought it was an "old wives tale" haha..

    Like taking a swim right after you have eaten..
  6. Apr 10, 2007 #5

    watch at around 41 secs
    Last edited by a moderator: Sep 25, 2014
  7. Apr 10, 2007 #6

    Doc Al

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    I'm not convinced that it's an "old wive's tale". I'd think that the repeated expansion and contraction of the filament would make stress fractures much more likely, making weak spots more likely to burn out. But I can't quantify how much of an effect that would be. Call the mythbusters!
  8. Apr 10, 2007 #7


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    They'll need to structure the experiment in such a way as to separate the repetive stress factor from the stress of rapid heating because it certainly is true that most general use incandescents fail when turned on.
  9. Apr 10, 2007 #8
    Heey...!! when you turn the light on the filament vibrates.. so maybe there is something about it after all:

    around 40 secs...
    Last edited by a moderator: Sep 25, 2014
  10. Apr 10, 2007 #9


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    In our old house, we had a dimmer switch on the chandelier over the kitchen table and that fixture at light bulbs like candy. The power filtered through that dimmer was really "notchy" and if it was quiet in the house, you could hear the filaments humming as you dimmed the lights.
  11. Apr 10, 2007 #10

    I think in that case, it was probably the contacts humming (arcing bulb to socket) from the AC current and resonating through the bulb.

    --at some harmonic maybe too.
    Last edited: Apr 10, 2007
  12. Apr 10, 2007 #11
    rewebster, I think so too... the filaments vibrate so rapidly so their hum would be almost ultrasound I think.. on the video you can barely see them shake and it's slowed down 40 times...
  13. Apr 10, 2007 #12
    OK naab---I have a thought WHY the filament 'vibrates/moves/shakes'---

    --why do you think it does?
  14. Apr 10, 2007 #13

    Meir Achuz

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    Do the experiment.
    Use a timer (or your old wife) for one bulb, and leave the other one on.
  15. Apr 10, 2007 #14
    I think it vibrates because of the moving electrons, but I'm not sure.. but you agree that the frequency of a possible sound from the filament would be high right.. so if you could hear the filament vibrate it would be a high pitch sound.. right?
  16. Apr 10, 2007 #15

    I think from the frequency of the AC current adds a component (which MAY create a sound which MAY add another component), but a DC lightbulb's filament vibrate/jump/move when first turned on too....so...

    do you have another thought?

    (that was a big hint...)


    OK--here's a bigger hint to what I think causes the movement

    Last edited: Apr 10, 2007
  17. Apr 10, 2007 #16
    I'm not familiar with DC and AC because I'm from Europe.. Is DC = and AC is the variable current? or the other way around..

    please the answer to why it vibrates.. :P it's late, I can't think..
  18. Apr 10, 2007 #17
    The filament is not perfect and sets up variations in heat and magnetic fields along the length of the filament. As the wire first heats up and the magnetic field is initiated, variations in these two cause the filament to bend AND to attract/repel for a while setting up a movement/harmonic vibration/jerking/twisting motion. Some of the more expensive bulbs are longer lasting because the filaments are made with less imperfections in material and consistency in diameter/shape.
  19. Apr 10, 2007 #18
    I wish I was as smart as you.. how old are you? :D
  20. Apr 10, 2007 #19
    I wish I could say
    I worked with Faraday.
  21. Apr 10, 2007 #20
    :P I just turned 18 last Thursday and I'm in my second year of high school out of three.. :D
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