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How long to turn off fluorescent lights?

  1. Jan 18, 2008 #1
    How long at least must I turn off my fluorescent lights to save energy?
     
  2. jcsd
  3. Jan 18, 2008 #2

    russ_watters

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    Forever would be best.....

    I suppose you mean how long would they have to be off to cancel out the effect of the starting current. Most modern fuorescents use electronic ballasts, which are fast starting and use very little extra power. So mere seconds is all it takes.
     
  4. Jan 18, 2008 #3

    mgb_phys

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    There was a chart for this but I can't find it.
    It was only worth leaving them on for the oldest technology fluorescent tubes ( the ones that flicker when you start them), which took something like 20seconds to break-even.
     
  5. Jan 18, 2008 #4

    turbo

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    Yeah, the inrush current to load the ballasts was much larger than the current required to maintain the arc, once established. If anybody here has balky fluorescents in their garage/attic/cellar that don't have diffusers, when you turn them on and they just glow faintly and sputter, you should quickly swipe your hand along the surface of the tube to create a static potential, and the light will usually come on, nice and bright. When my wife and I were considering renting an early 19th century brick house (cold,cold,cold) from my boss back 30 years ago, he was showing me through some closed-off rooms in the upstairs and one room had this type of lighting. It failed to do more than glow dimly and pulse, so I swiped the tubes to light them, and he said "I've got to spend more time with you. What else do you know?"
     
  6. Jan 18, 2008 #5
    A Mythbusters segment looked at this a while ago. I think their conclusion was that if you were going to be out of the room for more than a few seconds, turn the lights off.
     
  7. Jan 18, 2008 #6

    Integral

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    Looks like we have a good answer to the question, so it must be time for a story.

    I used to work in an interior (no windows) storage room, it was a long narrow room with exits to a hall way at each end. My desk sat near one of the exits. One day a professor was bringing in students for a brief conference through the exit at the far end of the room. As he left, he very consciencously turned out the lights. This left me sitting in the dark. I had to fumble my way over to a light switch, to turn the lights back on. A few minutes later, the same prof came in with another student. I sort of figured that he would see the lights on and figure out that he should leave them on. Nope, he shut them off again. After about the 3rd time I managed to get his attention to let him know he should leave the lights on.

    The moral of the story.. be sure the room is empty before you turn our the lights to save a few pennies worth of electricity.
     
  8. Jan 19, 2009 #7
    Question: Any suggestions on how to keep track of the number of hours the flourescent ceiling lights are left on in my daughter's dorm room? The lights are controlled by a wall switch. It's for a green project they're doing. We don't need to control the usage.

    Thanks!
     
  9. Jan 19, 2009 #8

    mgb_phys

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    Easiest way (without making any electrical connection to the wiring) is probably to have a web cam take a picture every 10mins and a bit of simple software to measure the brightness of the image.
     
  10. Jan 19, 2009 #9

    russ_watters

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  11. Jan 19, 2009 #10

    russ_watters

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    Hmm, that's a pretty good idea and if they only need a few days worth of data, they could sort it manually too.
     
  12. Jan 19, 2009 #11

    mgb_phys

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