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Efficiency of Fluorescent Lights

  1. Aug 24, 2005 #1


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    I read in a science question/answer book that it is takes as much energy to turn on a fluorescent light as it doesn to run it for 1 hour. So if this is true, it would mean that if you plan on using the light again within an hour, it is more efficient to leave it on, rather than turning it off and then back on again.
    Fluorescent lights are aleady much more efficient than incandecent light bulbs, but why not take the time to save an extra 10 of a cent.

    So has anyone else heard this before, or seen it somewhere else? I have only seen it in that one source, so I dont know if it is true, or if it is by how much.
  2. jcsd
  3. Aug 24, 2005 #2


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    I heard this on the grape vine, but thought it only applied to 'strip-light' style fluorescent tubes, rather than the 'energy saving' replacement light bulbs for domestic use. Will look it up properly when I get a spare minute...
  4. Aug 24, 2005 #3


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    Ok, here we go:


    The article also explains how long burns extend the lamp life, but since they use more energy, there's a trade-off point. The calculation needed is shown.
    Last edited: Aug 24, 2005
  5. Aug 24, 2005 #4


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    Yes, those were the ones I was refering to.

    So really, that book was wrong, or atleast very inaccurate.
    5 seconds, not even close to 1 hour.

    OK, thanks, I thought it sounded a little hokey.
  6. Aug 25, 2005 #5


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    This misconception may come from people thinking HID lamps (those big lamps at stadiums or in parking lots) work the same as fluorescents. An HID takes several minutes to heat up before operating and likely does use as much power in those few minutes as in the rest of the hour combined.
  7. Aug 27, 2005 #6
    I work on HID ballasts. A 100 Watt arc tube would use 200 Watts for
    maybe one minute. This is only twice, not 59 times the running power.

    If it used as much power to start (in one minute) as it did to run for the
    rest of the hour, then it would have to use 5900 Watts for the one minute.
    I assure you, it does not.

    What does take a couple of minutes is for the lamp to reach peak temperature
    and emit maximum light. The power by then is usually at the constant burn
    power even though the light is getting brighter.
    Last edited: Aug 27, 2005
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