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What is wrong with this pic V

Discussion in 'Question of the Day' started by Mayhem, Dec 29, 2004.

  1. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    We thought that we would post some pictures to generate discussion without any hints, tips or correct answers until we think that the time is right to do so.

    Here is the first picture - good luck!

    [​IMG]
     
  2. PATech

    PATech Member

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    I'm not all that much of a lighting guy, but judging from the big tumor that's localized in one area, it looks like someone has touched the lamp with their bare hands. That leaves hand oils and residues on the lamp, causing it to weaken over time and eventually fail. We have a lamp that looks like this sitting next to the lighting tools in the shop at school to remind people not to touch lamps with their bare hands.

    That's what seems to be wrong to me. Hopefully I'm right. I hope that everyone's having a wonderful holiday season.

    --Anand
     
  3. ccfan213

    ccfan213 Active Member

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    i also am not a lighting guy and you cannot see it in this picture well, but on the two lamps i gaffed to the booth wall a week ago that were like this to warn people it looked like the filaments somehow bent and touched that spot on the bulb.
     
  4. soundman

    soundman Well-Known Member

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    Ill third the idea of some one with gressey paws touching it.
     
  5. SketchyCroftPpl

    SketchyCroftPpl Active Member

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    I think also that its due to someone touching the light. We don't have any of these backstage cause in 4 years noone has touched the light and caused it to do that, we do however have a iron pipe handing on the wall which does the same job as having the broken light there to warn people not to touch it lol.
    ~Nick
     
  6. SuperCow

    SuperCow Active Member

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    Someone touched it, and the oils on their hand were transfered onto the quarts bulb. Quartz is used in theatrical lamps because it has a much higher resistance to heat, which is necessary fro the high-output tungsten filaments.

    When the oil came into contact with the bulb it stayed there. Oil will heat up quite rapidly, especially when the heat source is so near and so potent. As a result, one protion of the lam was far hotter than the rest of it. This caused the quartz to become unstable, since all the heat energy was concentrated in one spot, and the matter in one area was moving much faster than that surrounding it. When matter is moving faster, it also becomes more malleable (like warm plastic).

    The area within the lamp is filled with hydrogen, rather than air because hydrogen expands less under the influence of heat. However, this is not to say that it does not expand. So, when one portion of the quartz was weakened, all of the pressure exerted by the expanded hydrogen was exacted on that spot, causing it to burst, in the manner depicted in the picture.
     
  7. SketchyCroftPpl

    SketchyCroftPpl Active Member

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    Wow thats really complicated ... where did you learn all of that? They don't tlel us all that when we're learning it, all they say is that the light will expload and kill us and if the light doesn't kill us them the other techies will because the bulb for most of our lights is 40 bucks to change.
    ~Nick
     
  8. SuperCow

    SuperCow Active Member

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    I learned the hard way. Back when I was in the seventh grade, I touched a bulb, and the TD saw me do it. So, she told me all about why that's a bad thing to do. That was supplemented with stuff I learned in chemistry and physics. So, now I'm the one who gives the "don't touch the bulbs" lecture.
     
  9. SketchyCroftPpl

    SketchyCroftPpl Active Member

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    Ha Ha nice ... its cool that you could start tech in 7th grade. Our school doesn't allow us to untill 9th really. In 8th we're allowed to go to special workcalls for middlers and build small pits of set and two of us can run the assemblys that we have every week. Other than that you have to wait till HS which isn't alot of fun. I've given that lecture once or twice to Frosh but never in that much detail ... now I can scare them and make them think I'm wicked smart lol. Thanks
    ~Nick
     
  10. propmonkey

    propmonkey Well-Known Member

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    we have a collection of disfigured lamps that we keep backstage to show classes and new techies. we have one EGJ that is like a rainbow colors, its blue, red, silver, gold, and black. how could that happen?
     
  11. squigish

    squigish Member

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    It's not hydrogen, it's a halogen gas. I'm not sure which one, but my guess would be florine.

    Are you sure about the expanding less under the influence of heat thing, or was that just an educated guess? It's quite different than the explanation that I heard for why the lamp is filled with halogen.

    A standard incandesant light bulb consists of a tungeston filament surrounded by an inert gas (usually nitrogen or one of the noble gasses) and encased in a glass envelope. As electricity passes through the tungeston, some of it escapes and is deposited on the envelope. You can see the effect of this on some incandescant light bulbs that are near the ends of their lives, especially on the higher-wattage ones, in the form of black deposits on the inside of the glass. The result of this is shorter lamp life and reduced light output near the end of the lamp life.

    The solution is to fill the lamp with a halogen gas, which is very reactive. The halogen reacts with the tungeston as it is escaping from the filament and then deposits it back on the filament, instead of on the envelope. This lengthens the life of the lamp and also helps keep a more constant light output throughout the life of the lamp.

    As far as the need for quartz instead of glass, I don't know if it is something about the reaction between the tungeston and halogen gas that generates so much heat, or if it's just the fact that the lamp is burning at more than 500 Watts. My guess would be the former, because before they invented tungeston-halogen lamps, they used regular incandescants in the theater, and they were made of glass and large and spherical to dissapate the heat.

    Another advantage using quartz instead of glass is that because quartz is so much more heat-resistant than glass, you can put it closer to the filament, making the lamp smaller. This makes it easier to put the filament of the lamp precisely in the focal point of whatever type of reflector you're using, and results in more efficiant use of the light.

    Oh, and incidentially, I have a lamp at my school that has bulged out on one side but not ruptured, and the filament is bent into the bulge, but the lamp still works. We're saving it for when we need a lamp really badly just as a substitute until we can get another one. Maybe I'll take a picture of it next week and post it.
     
  12. SuperCow

    SuperCow Active Member

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    You're right on both counts. It is halogen, that was my bad. And the other was an educated guess (which I think is true, but I'll have to check).

    However, I do stand by my opinion that quartz is used because of its resistance to heat. I don't understand what you said about the bulb operating at over 500W, could you elaborate on that?
     
  13. squigish

    squigish Member

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    Quartz's higher heat resistance is precisely why it is used, the operating at over 500W thing was just my speculation as to why the Tungeston-halogen lamps get so hot, whether it has to do with the reaction between the tungeston and the halogen, or the high wattage of the lamp.
     
  14. Sombra2

    Sombra2 Active Member

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    it the same with car bulbs, a teacher gave us a halogen car bulb to test the resitance. little did i know, i get yelled at by my friend who is a car fanatic how i can't touch the bulb or it you'll add chemicals to the bulb to blow the blub. lucky the teacher never planned on using the bulb.
     
  15. lxdeptnz

    lxdeptnz Member

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    If you do touch it...

    If you are unfortunate to touch it, get a soft lint-free cloth and clean it all over with meths (isopropyl alcohol may also work). This will remove the grease from your skin and prevent the bulb from blowing up... If neccesary I have often worn gloves (cotton) when changing bulbs... this because it is a PITA to go back down the scaff tower and find some meths, and clean a bulb at the top of the scaff again :)

    HTH
    David

    PS I would also put my money on someone touched the bulb with bare fingers.
     
  16. ccfan213

    ccfan213 Active Member

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    do rubber gloves work?
     
  17. lxdeptnz

    lxdeptnz Member

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    I'm not 100% sure... i guess they would, if clean, however I've never tried them
     
  18. propmonkey

    propmonkey Well-Known Member

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    as long as they dont have that powdery substance on them.
     
  19. soundman

    soundman Well-Known Member

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    I use the wraper they come in.
     
  20. lxdeptnz

    lxdeptnz Member

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    All very well, except sone of the bulbs I get (over here in NZ) dont have wrappers:) but yes
     

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