Mailinglist Archive: opensuse (2831 mails)

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Re: [SLE] How to start a computer remotely - generic Q
  • From: Bruce Marshall <bmarsh@xxxxxxxxxx>
  • Date: Mon, 17 Jul 2006 19:24:25 -0400
  • Message-id: <200607171924.25462.bmarsh@xxxxxxxxxx>
On Monday 17 July 2006 19:05, James Knott wrote:
> A fluorescent tube that's turned off draws no power.  There will be a
> brief surge when turned on.  So, unless it's being turned off and on
> repeatedly, there's no way that statement holds.

I believe the statement that turning fluorescent lights on and off *does*
shorten there life. It's the process of starting up that takes its toll.


Misconception #2: Turning fluorescent lamps off and on wears them out right

Reality: Electric lights have a published rating for expected life. This
rating is in the hundreds of hours for many incandescent lights, and in the
thousands of hours for most fluorescents. Fluorescent lights have a life
rating based on how many hours they are left on every time they are turned
on. This is usually referred to as "burn time", and for fluorescent lights
the burn time is three hours.

Every time a fluorescent light is turned on, a tiny amount of the coating on
the electrodes is burned off. Eventually, enough coating is burned off, and
the lamp fails to start. Most full-size fluorescent lamps are rated to last
20,000 hours when left on for 3 hours every time they are turned on. This
means that the lamp has roughly 6,667 starts available to use up. (20,000/3 =

Longer burns extend lamp life. If you "burn" your fluorescent lamps shorter
than 3 hours per start, you use up your potential starts faster. If
you "burn" them longer than 3 hours per start, you use up your starts more
slowly. However, you are paying energy costs for the operating time of the
lamps, and the most efficient lamp is the one that is not on when it is not
needed. See Table 2 (at end of article) for the effects of longer burn time
on lamp life.

But longer burns use more energy. Operating a light when it is not needed is
simply spending money for no purpose. Today's rapidly rising electric rates
mandate that every building becomes leaner with energy use to control costs.
See Table 3 (at end of article) for a comparison of operating costs for a
typical fixture.

Find the trade off point.
There is a point where the amount of money you save from turning off the light
exceeds the cost of reducing lamp life by more frequent starts. If you use
the formula in Table 1 (at end of article) at $0.05 KWh, you come up with a
time of about 15 to 20 minutes for that point. As energy rates go higher,
that time becomes shorter. If you pay less than a nickel per kilowatt hour,
your turning-off point would be longer.

The kind of ballast you use may make a difference if you turn your fluorescent
lights off frequently. There are three different kinds of electronic
ballasts: instant start; rapid start; and programmed start. Which one you use
can influence your choice of how frequently to switch off your fluorescent
lights. Check with your ballast supplier, or contact a lighting specialist at
the Lighting Design Lab for more information on different types of ballasts.

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