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.
Switch on only when required. What made you think that switching a fluorescent light on and off wasn't a good idea?
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 saving.
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.
a popular myth
It's not an issue of thermal cycling :
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 tube.
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.
DG
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 degree.
I seem to recall, and emphasise seem, that Which back in the year dot when I started to subscribe, then suggested that a tube was best left on for 45 mins., if you were likely to re-enter that room. I still have that habit, but have reduced it to about 15 - 20 minutes.
Which one?
Could you point out please the particular myth you refer to?
Could you expand on that? It's a rather large webpage but all it says on lamp life is :
"Tube life depends on type of ballast (& starter where used), and how often the tube is switched on and off."
Which is correct but not specially helpful.
BTW Mr. Meow. we had another CFL fail yesterday after 6 months service in a cap down open fitting. It was a Feit electric 23 watt spiral offered for sale promising a 5 year life. The phosphor is quite significantly darkened and the top of the plastic end cap containing the electronic ballast has been toasted brown, what happened to the cheap Chi/Taiwa-nese pcb assy inside is anyone's guess.
DG
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 saving energy!
I've noted the same, and that later models have a breather hole in them.
Classic case of insulated electronics failing after prolonged 'on' periods.
I remember having this issue once with some gear I designed: A probe inside showed the unit took nearly ten hours to reach equilibrium - or would have. It generally failed after 7..;-) ten holes.. 5 in the top and 5 in the base made it totally reliable.
That is a common myth. Any extra power consumption surge during starting amounts to the amount of energy consumed in a second or two of steady operation - or less.
However, the cost of bulb wear from an extra start could require several minutes of off-time in order for electricity savings to outweigh that.
How many minutes? This depends on the bulb cost, electricity cost, starting method, and when the bulbs were made.
Modern fluorescents suffer less starting wear than older ones.
The "break even time" is less for ones 4 feet and longer than smaller ones. Lower wattage bulbs cost even more than 4-footers, and lower ratio of power consumption to bulb cost increases the "break even time".
The "break even time" varies with starting method because different starting methods cause different amounts of starting-related wear:
"Program Start" - this is used in some CFLs. The bulb does not come on at all until a fraction of a second to about a second after power is applied, then turns on without blinking. It may have a "rapid fade-on" during a fraction of a second. This causes the least wear, and is often used in CFLs of Philips and Sylvania brands (and some others but I can't remember who and I have not tried them all).
"Rapid Start" - bulbs come on instantly very dim, usually slightly flickery, stay dim for about half a second to a second, then quickly brighten over a fraction of a second. This is next-best to "Program Start" for minimizing wear from starting. "Trigger Start" refers to a variation of "rapid start" used on bulbs designed for "Preheat Start".
"Instant Start" - The bulbs are on instantly. Sometimes the brightness makes a sudden slight upward jump a fraction of a second after starting when the filaments achieve normal operating temperature. This is worse than "program start" and "rapid start" for starting-related-wear.
"Preheat Start" - usually has a "glow switch starter" or "glow bottle starter", rarely an electronic alternative. Bulbs usually blink a few times before they start and stay started. Since each blink causes starting-related-wear, this method is worst for starting-related-wear. Fluorescent lamps using this starting method, especially with bulbs 22 watts or less, are likely to have break-even times in/near the 15 minute to 1 hour ballpark, and should be left on rather than being turned off and back on shortly later. Electronic versions of starters that make the first starting attempt successful greatly reduce the starting-related-wear. Electronic schemes that make some determination when the filaments are properly preheated as well as making the first starting attempt successful are at least arghuably "program start" schemes.
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Now, how bad is it to turn off and back on a fluorescent lamp?
Case 1: 4-footer, 32 watt T8, instant start costing $2. I am guessing that a start with an instant start ballast takes 20 minutes off its 20,000 hour life. I am assuming also that this is with an electronic ballast that improves energy efficiency and also mildly underpowers the lamp/bulb (expect about 90% of "catalog" light output from the lamp/bulb), and per-bulb power consumption could be about 30 watts, usually not exceeding
32 watts. Another assumption - electricity cost 11 cents per KWH, which I believe is close to current USA average residential rate.Starting wear taking 20 minutes off the life of a $2 20,000 hour bulb costs .003333 cent. (Actually slightly less, since these bulbs are rated to last 20,000 hours with one start using rapid-start-method every 3 hours, and will last slightly longer than 20,000 hours if used continuously.)
To consume .003333 cent worth of electricity at 30 watts and 11 cents per KWH (.33 cent per hour) only takes .0101 hour, about 36 seconds.
Case 2: 15 watt spiral CFL purchased at a higher-side price of $7, instant-start. Assuming that the filament here is optimized a bit more for enduring starts, so I guess 15 minutes of life lost per start. (It could easily be 10 minutes or less.) Also, rated life expectancy 6,000 hours. (I know, now they make ones rated 7500 or 10,000 hours. But I want to be a little conservative here!) The life rating is with a start every 3 hours. So if it lasts 6,000 hours with a start every 3 hours and a start costs 15 minutes, then continuous operation avoids 2,000 starts over 6,000 hours and would add
500 hours to the 6,000 hour figure and make it 6,500 hours. Assuming that all my numbers here are good including ones that I am halfway pulling out of a hat, a start costs about .027 cent. If you get these bulbs in a $10 4-pack, then a start costs about .0096 cent. If you get these bulbs in a promotional $10 6-pack, then a start costs about .0063 cent. Now, to balance against 15 watts of power consumption at 11 cents per KWH (.165 cent per hour): .027 cent per start ($7 bulb) means "break-even" at 10 minutes .0096 cent per start ($2.50 bulb) breaks-even at about 3.5 minutes .0063 cent per start ($1.67 bulb) breaks-even at about 2.35 minutesLower wattage CFLs will tend to have longer "break-even" times, higher wattage ones will tend to have shorter "break-even" times.
Break-even time is also inversely proportional to electricity cost. It will be a little shorter in the metro areas of Chicago, Philadelphia and NYC.
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Where starting wear on lower wattage CFLs is a big issue, consider cold cathode ones. Those do not suffer any significant starting wear, and are often even rated for heavy blinking duty. They also have longer life expectancy than hot cathode ones of same wattage even without starting wear.
Downsides:
- Don Klipstein ( snipped-for-privacy@misty.com)
You have to read the fine print. Under that bit Five Years is the small print that bases the life on X number of hours per day.
Feit states 8,000 hours. From my experience with a few of them, I'd say they are close and have even exceeded that. I use them in some places in our warehouses for night lights and security lights that burn 24/7. Not a bad deal for a bulb that sells for 74¢.
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 believable.
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.
Why do you say they don't mind? Haven't you noticed that they almost always burn out at the moment they are turned on?
That's when they heat up, the filament expands (maybe faster than when it contracts on turning it off) and stresses on the filament are greatest.
If you leave a filament bulb on, it will generally last much longer than if you turn it on and off.
On or about Sun, 19 Aug 2007 04:07:06 -0400 did mm dribble thusly:
I was amazed no one had pointed out the error in that statement, and was about to comment. Sure enough, last message in the thread, and I'm scooped.
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