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Re: GBlist: Fluorescent lights - to switch off or not? That is



Fluorescent lamps work by causing a coating on the inside of the lamp to
glow.  That happens when an electrical arc passes through the tube,
causing mercury (generally) vapors to give off UV light, which the
coating converts to visible light.  An initial "excitiation" current is
required to heat up the electrodes and get the beam of electrons going. 
With current lamps and ballsts, this takes a second or so and most
ballasts have a separate circuit to provide that starting current.  
During that moment, the fixture draws significantly more than it does
during normal operation, but the excitation phase takes only a second or
so with current lamps and ballasts. With older ones it took somewhat
longer.

If the fixture consumed, in that second or so, the same amount of
electricity it would in three to four hours of normal operation, a
two-lamp fixture would be drawing several hundred kilowatts of power. 
Circuit breakers would pop and the wiring to the fixtures would have to
be much larger than it is to accomodate that surge.

It is certainly true than increasing the number of on/off cycles will
reduce lamp, and more importantly, ballast life, but that "penalty" is
relatively insigificant at probably any electrical rate versus the cost
of lamps/ballasts.  This effect is maximized if the lights are quickly
turned on/off.  Every lighting control that I know of has delays built
into it for this reason.

A space must be intermittently occupied to make the things work
economically.  If people are conscientous about turning off lights
there's an argument that substituting occupancy controls for all light
switches can lose energy in some rooms because the occupancy sensor will
leave the lights on in an office for minutes after someone has left. 
Conference rooms are the typical examples of where occupancy sensors
make the most sense.  

Warren C. Liebold wrote:
> 
> With all respect to your Dad, that has not been true for many years.
> The very long period of time you quote, I think, was never right, at
> least as stated.  If it were, you'd cause an enormous spike.  I think
> what they have meant is that for an instant you have a surge, which is
> 3-4 times the draw of the fixture under normal conditions.  That's
> different than a surge equal in a second or less to the energy which
> would have been used in 3-4 hours.
> 
> Further, if that were actually true with current fixtures and ballasts,
> no one would have agreed to go for occupancy sensors.
> 
> timex@pathcom.com wrote:
> >
> > Hal:
> >
> > Well, after reading all that, I will say a couple of things:
> >
> > 1) Your experts and mine disagree.  The engineer from Philips, )and
> > my father, both) said that the surge, which I'm assuming is what your
> > chap calls the inrush, costs between 3.5 and 4 hours of energy.
> >
> > 2) I was also told that switching on and off did not so much affect
> > the life of the lamp, as the life of the ballast.  I did not see
> > (though I admit I got somewhat dizzy reading that post) anything that
> > addressed that point.
> >
> > I'm going to file this post for rereading, as I just got through 14
> > hours of work, and may have missed more than most of the math.
> >
> > Marilyn
> > "Some ideas are so stupid that only intellectuals
> > could believe them."
> > -quoted from Lessons at the Halfway Point
> > __________________________________________________________________
> > This greenbuilding dialogue is sponsored by Oikos (www.oikos.com)
> > and Environmental Building News (www.ebuild.com). For instructions
> > send e-mail to greenbuilding-request@crest.org.
> > __________________________________________________________________
> 
> --
> Warren C. Liebold
> 
> wliebold@waonline.com
> wliebold@pppmail.nyser.net
> 
> Director of Conservation
> New York City Department of Environmental Protection
> __________________________________________________________________
> This greenbuilding dialogue is sponsored by Oikos (www.oikos.com)
> and Environmental Building News (www.ebuild.com). For instructions
> send e-mail to greenbuilding-request@crest.org.
> __________________________________________________________________

-- 
Warren C. Liebold

wliebold@waonline.com
wliebold@pppmail.nyser.net

Director of Conservation
New York City Department of Environmental Protection
__________________________________________________________________
This greenbuilding dialogue is sponsored by Oikos (www.oikos.com)
and Environmental Building News (www.ebuild.com). For instructions
send e-mail to greenbuilding-request@crest.org.
__________________________________________________________________


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