Luminosity vs voltage.

Discussion in 'General Electronics Chat' started by PRS, May 20, 2011.

  1. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
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    Why does luminosity fall off non-linearly with respect to the applied voltage? I hooked up a 277 volt lamp to a 240 volt source and the lamp was too dim for satisfactory service. (Boss at a car dealer bought these lamps, thinking he was getting a good deal). Experimentally, this was the case.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You need access to a 480 Volt 3 Phase service line.

    The phase to ground voltage of this service is 277 volts. You would have three seperate 277 volt feeders from the 480V3P line. You can call the power company and ask what is involved in getting this service provided, or you can look for some 220/240 volt to 277 volt transformers(these are rare, hard to find and not cheap), but on the other hand, any power hook up work done by the power company will not be cheap either.

    Looks like $$$ either way you go. If these are Fluorescent lights, it would be easy, and much cheaper, to get a different voltage ballast and replace them. Then again, new fluorescent light fixtures cost about the same as a new ballast in most cases. You may get lucky and find something LESS expensive, but you WILL need to spend $$$ to get these lights working.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. #12

    Expert

    Nov 30, 2010
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    News Flash: Ignorant boss buys stuff that won't work because it's cheap, then tells me to make it work.

    Been there, done that...so many times!

    Try not to call him an idiot if you want to keep your job.
     
  5. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
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    Thanks Kermit2 I was actually asking about the physics of exponential light decay due to voltage drop. This incident happened some years ago. I suppose I could look up the answer myself, but I was wanting to get on the board. ;)
     
  6. Markd77

    Senior Member

    Sep 7, 2009
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    If it was an incandescent bulb then there's at least a couple of things going on.
    Power is V^2 X R so the power is reduced by a bigger amount than the voltage is.
    If the power is reduced then the filament temperature is lower so less of that power goes into producing light and relatively more into producing heat.
     
  7. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
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    That article shed a lot of light. Thank you very much! I had a hunch this would be an interesting topic and I suspect I should have posted in on the physics forum to keep it present. I'll repost it there and let's talk about it.
     
  8. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
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    LOL! I already knew it wouldn't work because of previous experience in LA when we gutted a hospital wing and all the workmen took 277 volt lights home to put them in their workshops at 240 volts. I told them it might work but then got the bad news. Live and learn. At least my lesson was free.
     
  9. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Read beenthere's link. It says that most of the light from an incandescent is infrared, a frequency of light the human eye can't see and so is wasted power.
     
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