Turning Off Lights

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    • #249533

      > …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
      >truth…

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

      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
      minutes.

      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
      some
      interesting thoughts but it kind of gets down to where
      the
      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
      likely
      (and convenience and reduced family stress is worth
      something…
      just not very much…).

      Jay

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