I have understood that switching fluorescent lamps - tubes - on and
off was not a good idea and that they should be switched on and left
on. Unlike filament lamps which do not seem to mind.
How do the modern CFLs compare/suffer etc etc?? I know that they can
take a minute or two to warm up and maximise their light output.
If they should be switched on and left on, then they begin to defeat
the very purpose of having energy saving CFLs fitted.
It was either a common misapprehension, or used to be different with
older tubes. I certainly remember an "order" going around school in the
early 70's to NOT switch off lights during break-times as it took more
electricity to re-start them, than to leave them on for 20 minutes.
It was a complete redherring then and still is. Yes the current is higher
in order to ignite the tub, but given it lasts for a second or so. As long
as the tube is switched off for over, say 5 seconds, there'll still be a net
When, and with fittings of what vintage? Tubes and control gear have
been improved continuously, changing out of all recognition since the
end of the war.
Sorry not the case, there is still an optimum way of operating the
This sort of advice was originally intended for industrial users who
had a machine shop or a weaving shed etc lighted with hundreds of
fluorescent fittings mounted on the ceiling over the machines. These
tubes were replaced on a planned preventative maintenance basis whilst
the plant was shut down for (annual ?) holidays. To have tubes fail
between times was very expensive, the electrician would have to work
above the machines (which would have to be stopped) and there was the
possibility that a tube would be dropped or broken contaminating the
workplace with broken glass, and if that was a loom would include
hundreds of feet of very expensive cloth.
That's not the issue (even if it's true, I've not seen it mentioned
elsewhere), shortening of the tube life is the issue. Modern control
gear can be a lot better than old stuff, but as always the best
equipment is more expensive and not always used.
Nowadays domestic users of fluorescent tubes need not concern
themselves too much, but "Best Practice" is "Best Practice". If you
have a fitting that requires a lot of effort to get at (above the
stairs say) it makes sense to get the most out of the tube.
It's very much the issue! I recall stories as the poster had where the
starting of a fluorescent tube was equivalent to 1/2 hour running.
I have read the article and it confirms what I know. I was answering a post
outlining a supposition put forward in the 70's. At that time the ballast
would be an inductor and the starter would be gas filled device.
It's a great shame that the article doesn't qualify "Lamps operated for
typically less than 3 hours each switch-on will normally run out of the
emission mix before other parts of the lamp fail". That is the most common
failure mechanism for lamps. I recall figures which suggested that whilst
the lamp lifetime when "on" was shorter, the act of switching it off when
not needed actually increased the "real" life time of the lamp as well as
Analyse that statement logically and you will see it makes no sense...
How much current would be drawn by say a single 56W tube? 230mA.
How long does it take to start? say 3 secs
So the current drawn in those three seconds would need to be 600 times
(i.e. 1800 secs over 3) the nominal current so as to consume the same
amount of energy, or 138A.
Any guesses as to how many tubes with that sort of inrush current you
could start on a circuit protected by a 6A breaker without tripping it? ;-)
First off, it's true, and it may be the basis for the original post,
so it's worth discussing.
Secondly, I would say that it does make sense**, but it's not accurate
and for someone who knows anything about the topic, it's not
Something that makes no sense, to me, would be something whose
intended meaning I can't discern.
**A lot of things use more electricity on start-up, so the sentence is
not illogical. But the numbers are wrong.
Well, Duh! His obvious point was that if you look at the real facts,
which he clearly presented, then it makes no sense, because the
current required in the few secs of startup would be huge. And I
think your definition of "makes no sense" equals "can't discern
intended meaning" isn't exactly mainstream. For example, if someone
said that Mars revolves aroung the Earth, the meaning is quite clear,
yet any reasonable person would say that makes no sense.
I accept that the claim has been made - I have heard people making it as
I also expect that is is a corruption of the original research that was
looking at overall costs including lamp life and not just running costs.
It has just that much of the detail has been lost in the Chinese
whispers along the way and it has been reduced to an absurdity
concerning just energy costs.
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember John Rumm
The first time I read about this was nearly 30 years ago in New
Scientist, where the article made the point it was about overall
lifetime of the lamp and fittings, rather than electricity consumption.
In that original article there was bare mention at all of the start-up
energy cost, probably because it was insignificant. The piece
illustrated how the lifetime of a lamp was reduced by multiple starts,
and showed that it was more economical *at that time* to reduce the
number of starts, or once started, leave the lamp on for a while.
At that time, with the fluorescent lamps and fittings available and the
energy cost of the day, the break-even point was 20 minutes.
It's usenet, so it's not unknown for the ill-informed start an argument
without knowing the full story.
Many thanks for your support. I was trying to make the point, admittedly
badly, that in the 70's that there was the misapprehension that starting a
fluorescent tube took an inordinate amount of energy. I think we both agree
that this is very untrue.
How does that contradict what he said? And it is the issue, like he
They said the same thing about lncandescent lights, btw, and I
believed it until I thought about it. My line of thinking was. If
turning the light on was equivalent to using 10 minutes of
electricity, imagine the time it takes for the bulb to get to full
brightness and imagine running 10 minutes worth of electricity through
the filament in less than a second. That's a half amp or so times
36,000 (sec./10 minutes). That's 18,000 amps through my lightbulb.
Wow. Maybe I'll rejuvenate a cadaver next time.
I haven't read the url below, so I'll leave that for later.
On Sat, 18 Aug 2007 22:56:48 +0100, Derek Geldard
:Nowadays domestic users of fluorescent tubes need not concern
:themselves too much, but "Best Practice" is "Best Practice". If you
:have a fitting that requires a lot of effort to get at (above the
:stairs say) it makes sense to get the most out of the tube.
Yes, DG has it right. The issue is NOT energy usage here but the life of
the bulb. Turning a CF on and off a lot DOES shorten the life. It may
have 10,000 hours MTBF, say, but if you turn it on and off 10,000 times
the life isn't apt to be 10,000 hours! I don't know if the bulbs have
gotten better that way, but what HAS been getting better is the cost of
the bulbs. They still aren't nearly as cheap as incandescents, but the
economy of the situation has incandescents out of the picture. I haven't
bought one in quite a few years.
If I only need a CF on for a few seconds, in my workroom, say, I
generally use a flashlight rather than turn on the overhead light for
10-15 seconds in order to find what I need. At the ceiling are two CF's,
and I don't want to wear them out. I've heard that nowadays the life is
only shortened maybe 5 minutes, but I suspect that's quite inaccurate. I
have had several CF's fail way before they were supposed to. There's a
circular one in my kitchen that would probably cost me over $10 to
place, and the one it replaced lasted maybe 10-15% of the supposed life
1. Heat - see if it gets unduly warm where that light is. Rated life is
with ambient temperature 25 degrees C (77 degrees F).
Better ones should have only slight incidence of early failures if it
gets a fair amount warmer. But if you have an enclodure around it, try
removing the enclosure.
2. Was it a brand other than GE, Sylvania or Philips? Most "circline"
lamps that I have seen to go into screw sockets have been by Lights of
America so far, and I have had a disproportionate share of LOAs die young.
(However, I have only bought one LOA since 2001 so they may have
improved.) I have also generally experienced LOAs (as well as Maxlites)
to be a little dimmer than others of same claimed light output.
- Don Klipstein ( firstname.lastname@example.org)
In the case of CFL's I recall that while they do take more energy on
start-up, the break even point comes after a matter of a few seconds.
So, for practical purposes, they should be turned off when not
needed. With all of the ones I've seen, the bigger problem is what
was already noted. They take a couple mins to reach full output.
Even worse, the output is terrible for the first 30-60secs. For that
reason, I leave them on more than I would a regular light, thinking
I'll need it again in maybe 10 mins. But overall, I'm pretty sure
I'm saving a good bit on energy.
I don't think the startup energy is the issue, it is the wear and tear on
the lamp from thermal cycling which shortens the life. I leave a CFL on in a
(very dark) hall and landing all day, and they last years.
It's not an issue of thermal cycling :
It's during start up that most of the wear and tear is done to the
tube filaments. The filaments are coated with an emission mix which is
sputtered off causing blackening of the tube ends. When most of it has
gone the striking voltage of the tube rises until in the end stage the
tube will not strike any more. Some electronic ballasts can detect
this condition coming and shut down, other earlier/cheaper electronic
ballasts will continue to try to start the tube and end up being
damaged by overvoltage and fail. Simpler inductive ballasts with glow
switch starters do not fail but will typically run for months with the
tube flashing on but failing to start and then cyclically restarting
from scratch, this causes a nuisance and should not be allowed to
continue as eventually the starter can overheat melting it's mounting.
Actually it was that the total cost was more to turn them off than to
leave them on for periods of about 20 minutes or less. The largest factor
was the cost of replacing the lamps because cycling them reduced their life.
Note those figures were based on commercial applications and included the
cost of the maintenance man doing the replacement. This was one of the
studies we took apart in my statistics class while working on my economics
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