Turning Off Lights

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  1. #1
    Jay Williams

    Default Re: Turning Off Lights

    > ...thoughts on turning lights off and on...you save
    >by turning them off when you are out of a room....
    >(possibly) not a real saving, as it (might) cost more
    >to turn them back on. So, not sure of what is the

    The TRUTH, as in so many cases, is: It sort of

    Most people in the U.S. pay in the vicinity of $0.07
    per kilowatt hour (that is, using a 1,000 watts of
    electricity for one full hour costs a dime or less -
    as does using 100 watts for 10 hours or 10 watts for
    100 hours).

    So, if you leave a 100 watt bulb burning all night (or
    day) you'll find an extra dime on your bill at the end
    of the month.
    If you turn it off for, say, 15 minutes while you
    aren't in a particular room for a little while, you'll
    save in the order of a quarter of a penny (given that
    it takes a dime to run the 100 watt bulb for 10 hours
    which is a penny for 1 hour and
    15 minutes is one-quarter of an hour).

    And you'll notice that more and more it is becoming
    common to find that the lights are off in restrooms
    when you first go in,
    copy machines are "sleeping" until you wake them up,
    and there
    are timers or sensors on lights in public places. It
    all adds up!

    But life is never quite so simple. The typical light
    bulb has a low
    resistance when it is "cold" (turned off and not
    giving off light)
    and a higher resistance when it is "hot" (turned on
    and illuminating
    the room). When you first turn on a filament-style
    electric light
    there is a surge of current larger than normal through
    the cold
    bulb until it warms up. So a person would be correct
    in saying
    that for some short period of time it takes a little
    more energy
    (which is turning your meter) to warm up the bulb than
    it would
    to just have left the bulb on in first place.

    Opinions vary as to where the break-even point is
    between just
    leaving the bulb burning versus turning it off and
    then back on
    but it's most likely a time measured in seconds...not

    But, there is another "gotcha" in all this. Turning a
    light off, letting
    it cool down and then turning it back on again
    subjects the bulb, as
    we said before, to a momentary surge of current
    through the filament
    which stresses the bulb both electrically and
    mechanically and leads to an
    earlier failure (I'm sure that you have noted that
    many times a light
    bulb will fail with a blinding flash of intense
    blue-white light just when
    you flip the switch on...the cold surge at work and
    the filament will
    be broken - you can sometimes hear it rattling around
    inside - and there
    may be dark smudges visible even through the frosting
    that indicates
    that something violent happened inside the bulb).

    So,what does a new bulb cost and how much did we
    shorten the
    life of the bulb by turning it off and on to save a
    little electricty and
    will we have to replace the light switch sooner than
    we would have
    if we weren't always flipping it off and on...off and
    on...off and on...
    until it too fails mechanically.

    From what I've seen a lot of really sharp folks have
    put a pencil to the
    numbers for one reason or the other and come up with

    interesting thoughts but it kind of gets down to where
    assumptions are driving the results.

    I really struggle to conserve electricity (and gas and
    water and...)
    by putting in the compact flourescents and turning off
    lights in rooms
    that nobody is currently occupying and hardly have a
    monthly electric bill
    over $15.00 for about 1200 square feet (2 BR, 2 Bath
    apartment) but
    I'm not sure that everyone would actually want to live
    like that.

    For me, the lights go off as I leave a room unless I'm
    absolutly sure
    that I will be back in the room within a couple of
    minutes (not
    5 or 15 but 1 or 2). Could I prove that it's EXACTLY
    the cheapest
    way to do things beyond a shadow of a doubt? Not very
    (and convenience and reduced family stress is worth
    just not very much...).



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  2. #2

    Default Turning Off Lights

    Boy oh boy, I never thought I'd learn so much about light bulbs.

    Jay Williams <nwslttrs02@yahoo.com> wrote:> ...thoughts on turning lights off
    and on...you save
    >by turning them off when you are out of a room....
    >(possibly) not a real saving, as it (might)


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