From: SFPhysics@aol.com
Date: Wed Nov 21 2001 - 01:43:38 PST
From: SFPhysics@aol.com Message-ID: <96.1d81d8de.292cd14a@aol.com> Date: Wed, 21 Nov 2001 04:43:38 EST Subject: Electricity Questions
1. On a computer, if you have the settings such that
the monitor turns off after a certain amount of time,
does it save more energy to actually turn it off?
2. When exiting a room with fluorescent lights, there
is someone who contends that one should not turn them
off unless you're going to be gone for at least an
hour because it takes so much energy to start them up
again. This seems ridiculous. Does anyone know how
much energy it takes to start them up?
Thanks,
damon
>>
Greetings Damon:
1) First let me state that our society with its propensity to want everything
now, at the touch of a button, has generated a hundred little energy vampires
in our homes and businesses. Such a device is the standby circuit in a
monitor. Turning a device like a computer monitor completely off is better
than leaving it on standby but the difference is small. On standby a large
monitor may only be drawing 7-8 Watts typical. That is not much and it keeps
the monitor alert to a sync signal from the computer which would turn it
fully on. But multiply this times a whole city full of monitors, tens of
thousands, and you get into some real power. When fully running the average
monitor can draw 100+ Watts so standby is much better than leaving banks of
monitors on as was the practice of banks, businesses, government agencies,
etc., in the past before monitor standby mode "energy savers" were
introduced. I set my monitor to shut off if I am not active on the computer
after 10 minutes. When I am not using the machine overnight, during the day,
while I am gone from the house, weekends away, etc., a master switch on an
outlet strip (that is also a spike protector) shuts the whole computer system
off. Then the draw is zero. This also saves on the hard drives in the CPU.
2) Modern thin tube fluorescent lamp systems do not have a large initial
current draw. Turning them off saves energy, period. The only thing that
would make you not want to turn of the light is that cycling them on and off
does tend to shorten the life of the tubes, the ballast system, and the
control switch. So, turning them off for just five minutes while you are out
of the room gives you very little gain. Wear on the wall switch leading to
an early call for an electrician will eat up all of the savings gained for
years. This becomes a judgment call. If you know you are leaving a room for
a half-hour and you do this several times a day then the time does add up.
For a large office space with many Kilowatts of lighting this could add up
quickly. Conversely for a cubical or small room the gain would be minimal
and leaving the lights on might make more sense. The mechanical wear on the
switch is the main concern.
The idea that turning on a light, even the old Edison carbon lamps of the
1890s, uses more power than running them for a long time has never been
correct. Incandescent lamps do draw high currents for short duration but
that quickly drops as they reach operating temperature. Fluorescent lamps
have no such large starting current.
Happy Thanksgiving to All,
Al Sefl
Physics Teacher at Large
And who will be larger after Thanksgiving...
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