Flourescents: Turn off vs leave on??
Job
| Posted in Energy, Heating & Insulation on
I’ve heard said that turning flourescent lamps on and off shortens the life of the lamp, so one should just leave it on always. Sounds counter intuitive to me, + cost of elec a factor? Any ideas? Thanks. Paul
Edited 12/28/2002 3:58:38 PM ET by paulz
Replies
It's my understanding from previous reading that flourescents use quite a whallop of juice to charge the starter and get them fired up to the point that turning them on uses the same juice as around twenty minutes to a half hour of leaving them on. I don't know if the parts wear out faster or not. My office lights are flourescent and stay on almost all the time.
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
"...turning them on uses the same juice as around twenty minutes to a half hour of leaving them on. "
I've heard that too, but don't buy it. If it took that much to get them started, a 40 watt bulb would have to have a 20 amp circuit to get it started.Eat well, stay fit, die anyway.
Not so Boss. Short surges can be handled by lower rated circuits. For instance, a fifteen amp circ saw can draw way more than that to start cranking. My WH molder is rated for 29amps at 120V but on startup it will draw fifty or more, depending on temperature and length of cord. You are not likely to melt your house wiring down by turning on the flourescent lights but if you stand there flicking the switch on and off several times it will heat up and mtybe shorten it's life..
Excellence is its own reward!
"The first rule is to keep an untroubled spirit.
The second is to look things in the face and know them for what they are."
--Marcus Aurelius
I turn mine on and off as I leave the room. The tubes last a very long time, even if I am shortening their life. I believe that turning them on pulls a momentary high current pulse, but within a second or two, it's running normal operating current. I have heard that its more efficient to leave them on for at least 30 minutes (power wise), but that's not true. I could see where the labor costs enter into the equation, it has no effect on my situation though.
The published lifetimes of the flourescents bulbs (10,000 to 20,000 hours) is based on them running a minimum of 4 hours at a time. I don't have any numbers of how much life is lost with each on/off cycle. But in a home application they don't last near that long because of the frequent on/off cycling.
BTW, I saw a study that indicated that flourescents with the electronic ballast where more tolerant of short on/off cycles.
The trade off is between the material and labor costs of replacing the lamps, tubes, versus the cost of electricity. For a homeowner the labor is cheap if they do it themselves. The tubes vary in cost with size and sophistication.
The numbers involved with the lights in many department stores during the early 70s, a time when electricity was cheap, worked out in favor of keeping the lights on 24/7. The kicker was that the ceiling in many of these stores was pushing 20' meaning that you needed a Baker scaffolding and a small crew to do the job.
Also the efficiencies involved usually meant that the entire store was done at the same time. In fact many locals back then would grab the lamps out of the back alleys knowing that most would have a good deal of life left in them. Many a church or charitable organization got free lamps this way.
In residential situations selection of fixtures should take this into account. Florescent lights are good for kitchens, shops, porch lights or any other location that they are likely to be run for two hours or so at a time. Hallways, baths and most bedrooms are not so good due to the way these rooms are commonly used.
The big companies (like IBM, GE, City Bank, etc.) study these things to death, mostly because fractions of a cent times 10,000 instances can add up. While I do recall seeing some ideal number, that changed with the electricity and labour rates BTW, they usually go for simple guidelines (higher penetration of compliance is always more fruitful than rules that aren't followed). The last set of rules that I can remember were:
1) lights go off at EOD, lunch, and any time you go to a meeting.
2) do not turn off the lights to go to get a coffee, to take a nature break, to pick up printouts/mail, or do any errand that will take 15 minutes or less.
Phill Giles
The Unionville Woodwright
Unionville, Ontario
Someone got snippy a few days ago when I suggested he contact the manufacturer with his technical question, since I thought few other sources would have the time, instrumentation, and laboratory necessary to give him an answer that was correct. But it only happened once and I'm not going to let it faze me!
Sorry for the digression.
According to the General Electric lighting catalog, for a typical (say a Trimline T8) lamp, the rated average life if left on 12 hours each time it was started is 24,000. If left on only 3 hours each time it was started the life drops to 20,000 hours. So, frequent starting does have an effect on lamp life.
In college I asked my electrical engineering professor if starting a fluorescent lamp uses significantly more electricity than leaving it running. He said no, the starting current is only slightly more than the operating current, and is very brief. Since that was over 25 years ago, I don't remember the numbers.
Why would I believe a light bulb vendor's recommendations for extending the life of their bulbs?
You don't have to believe them if you don't want to.
They are not making recommendations as to how to extend the life of their lamps. They are providing technical data that lighting designers require in order to make an intelligent choice. Large, reputable manufacturers tabulate useful data for all the thousands of lamps they make, including lumens, life, color temperature, color rendering index, and the effects of other factors such as voltage, ballast factor, high frequency operation, temperature, luminaire temperature, etc. They specify how such tests are conducted, according to, say, such and such an ANSI standard, using calibrated instruments, traceable to NIST.
If the data they give is materially inaccurate, they would be committing a fraud. I doubt any long standing company would do that.
Why wouldn't a company want you to get the most out of their products? If you're happy you are likely to return again and again. That's how companies get to be a hundred years old or more. Doesn't an automobile company tell you how often to change the oil, filters, etc?
I would not trust most used car salesmen, but I would trust published technical data from an established corporation.
By the way, I don't work for GE or any related company.
Nobody has mentioned temperature effects, or did I miss that post? . If the room temp is at 50F leave them on all day once you turn them on, or you will replace a LOT of bulbs (old & wise experience, plus lots of mfg test data!)
As to energy calc, typical breaker takes less than say 1 second to trip at much over 20 A (again, see mfg data for breakers)0r alternatively, the lamp lights in less than 1 second -- for the simple 1 second example, 120 V* 20 A * 1/ 3600 = .00066 kw-hrs, thus starting is same as running for 3600*.00066 kw-hrs/.2 kw < 12 seconds.
Thus, as others have said, it is only the replacement cost that you are concerned with. If you are in FL or HI at 80 or 90 F all the time, turn'em off when you leave other plaes use a sliding scale (again, as said before, see mfg data) as temp drops, leave'em on all day for 50 F if you are ever going to turn'em on again that day.