[sci.electronics] fluorescent vs. incandescent

smf7s@hudson.acc.virginia.edu (friedman steven michael) (04/17/89)

	I know that fluorescent lights are more efficient than
incandescent lights, but use a lot of power during start-up; whereas
it costs nothing to flip an incandescent bulb on and off, but is more
expensive to run over time.  My question is where do the efficiency
curves meet?  That is, how long does one need to keep a light on
continuously before it becomes more efficient to switch from
incandescent to fluorescent? (Obviously the functions would cross in
different places, depending on wattage).

				Steven M Friedman

Mail path:	smf7s@virginia.BITNET
Voice path:	(804) 295 0235 -- Home
           	(804) 924 7625 -- Office

larry@kitty.UUCP (Larry Lippman) (04/17/89)

In article <1369@hudson.acc.virginia.edu>, smf7s@hudson.acc.virginia.edu (friedman steven michael) writes:
> 	I know that fluorescent lights are more efficient than
> incandescent lights, but use a lot of power during start-up; whereas
> it costs nothing to flip an incandescent bulb on and off, but is more
> expensive to run over time.

	The "starting" current of a fluorescent fixture is NOT significantly
more than its operating current, and in some fluorescent lamps the starting
current is in fact LESS than the operating current.

	Even in a simple "preheat" circuit with a manual starting switch -
like a desk lamp - the filament current is of the same magnitude as the
ionized lamp current.  Fluorescent fixtures with preheat circuits using
starters usually fire the lamps in 1 to 2 seconds, and during the starting
interval the fixture current does not result in any significant excursion
above operating current.

	Fluorescent fixtures with "rapid-start" circuits (probably the
most common circuit in use today in North America) have a starting current
that is LESS than the operating current, since the filaments remain on
at ALL times.

	Fluorescent fixtures with "instant-start", "trigger-start" and
cold-cathode circuits have about the same starting as operating currents.

	On the other hand, incandescent lamps ALWAYS have an inrush
current that is MUCH higher than operating current since the resistance
of an incandescent lamp filament is MUCH higher when hot than when cold.

	Sorry, but that's just the way it is.
 
> My question is where do the efficiency curves meet?

	They don't.

> That is, how long does one need to keep a light on
> continuously before it becomes more efficient to switch from
> incandescent to fluorescent?

	Sorry, but this is a non sequitor.

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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haynes@ucbarpa.Berkeley.EDU (Jim Haynes) (04/17/89)

In article <3098@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>In article <1369@hudson.acc.virginia.edu>, smf7s@hudson.acc.virginia.edu (friedman steven michael) writes:
>
>> That is, how long does one need to keep a light on
>> continuously before it becomes more efficient to switch from
>> incandescent to fluorescent?
>
>	Sorry, but this is a non sequitor.
>
Well, now I remember reading somewhere once long ago and far away that the
fluorescent lamp has a limited number of starts, whereas the incandescent
doesn't, so a figure of 10 minutes was given - that is, the cost of starting
the fluorescent in terms of reducing lamp life balances the cost of leaving
it on in terms of power consumption.  All of which sounds pretty wishy-washy
now that I think about it.  And actually incandescents must have some limited
number of starts also, since the thermal shock of turn-on probably reduces
life somewhat.

Thanks, Larry, for your previous posting on the various circuits and
principles of fluorescents.  I'm an E.E. too, but of course they don't
teach that kind of thing in engine school (tho I too had to endure all
the polyphase rotating machinery as you mentioned).  There ought to be
a book on "The Way Things Work" written at the level of engineers.
Like, I didn't get any answer to my earlier question about microwave
ovens.  Which was that the only magnetrons I know anything about take
terribly high voltages to operate; and the microwave oven doesn't seem
heavy enough to contain that kind of power supply.

haynes@ucscc.ucsc.edu haynes@ucscc.bitnet ...ucbvax!ucscc!haynes

"Any clod can have the facts, but having opinions is an Art."
        Charles McCabe, San Francisco Chronicle

anand@vax1.acs.udel.EDU (Anand Iyengar) (04/18/89)

In article <1369@hudson.acc.virginia.edu> smf7s@hudson.acc.virginia.edu (friedman steven michael) writes:
>incandescent lights, but use a lot of power during start-up; whereas
>it costs nothing to flip an incandescent bulb on and off, but is more
>expensive to run over time.  My question is where do the efficiency
>curves meet?  That is, how long does one need to keep a light on
>continuously before it becomes more efficient to switch from

	What I've heard is that it's not so much the start-up cost, but
the wear on the tube from switching it on/off, versus the cost of the
power it uses.  About 7 years ago, I was told that flourescents should
not be turned off if they're going to be used in the next hour (that
was for a room full:  I'm assuming this scales...therefore it should be the
same for fewer lamps of the same wattage (40) ).  Anyone know about
sodium/mercury vapor?

							Anand.  

kanner@Apple.COM (Herbert Kanner) (04/18/89)

>
>Thanks, Larry, for your previous posting on the various circuits and
>principles of fluorescents.  I'm an E.E. too, but of course they don't
>teach that kind of thing in engine school (tho I too had to endure all
>the polyphase rotating machinery as you mentioned).  There ought to be
>a book on "The Way Things Work" written at the level of engineers.
>Like, I didn't get any answer to my earlier question about microwave
>ovens.  Which was that the only magnetrons I know anything about take
>terribly high voltages to operate; and the microwave oven doesn't seem
>heavy enough to contain that kind of power supply.
>

While we are talking about how things work, perhaps someone can
enlighten me about a fluorescent flashlight.  This is an Everready
(made in Hong Kong, I think) flashlight that takes four AA batteries,
has a three-way switch for off, conventional flashlight, and miniature
fluorescent tube.  My question is, what circuit is behind the
operation of the fluorescent tube and how is the discharge started.
It does not look as if it has filaments, but it is hard to be sure.

Thanks.


-- 
Herb Kanner
Apple Computer, Inc.
{idi,nsc}!apple!kanner
kanner@apple.com