Fluorescent Lights automatically turn off/on

[Fluorescence]

hello,

I recently went to the conveniences in Tesco, Aldershot , UK... and the lights were out when i walked in but came on automatically as i entered.

The lights were many small fluorescent tubes.

since this is a busy shop...these lights will be OFF and ON'ing all day long..

do you think this is wrong because fluorescent lights wear out very quickly if turned ON/OFF often ?

 

[dpc]

Wrong in what way? The tradeoff is between lamp life and energy costs associated with starting the lamp and keeping the lamp energized. Most recent data I have seen indicate that if the lamps are off at least a few minutes, it is more cost-effective to turn them off. This is contrary to what we were taught many years ago, but seems to be the current thinking.

Back when I started my career in the 70s, many office building kept their fluorescent lamps on 24 hours a day.

 

[IRstuff]

The power consumption myth has been long debunked. The inrush currents typically cited last a few seconds, max. Assuming even a factor of 10x in starting power, the payback period is less than 1 minute.

The thermal or other shock can be dealt with using soft-start approaches. This must also be considered in light of keeping the light on 10 or 100 times longer than needed, so there is already life loss by keeping the light on.

TTFN

FAQ731-376

 

[MacGyverS2000]

And inrush currents are most often associated with filament bulbs, not fluorescents (though a case could be made for the higher current used during the high-voltage strike pulse).

Dan - Owner

http://www.Hi-TecDesigns.com

 

[VEBill]

The TV show 'Mythbusters' recently (rerun?) had an episode with this question. They're sometimes a bit scientifically illiterate, but this time I didn't see anything wrong with their methodology.

They found that the lights with the worst start-up were the old fashioned fluorescent tubes (with the heaters in the end) and old-school ballast. But even those were only 23 seconds payback for switch-off. All other lights technologies were even less. In other words, the start-up power surge is trivially small in terms of financial impact.

And with respect to excessive on-off cycles, lights are extremely cheap compared to the cost of the power they use.

 

[dpc]

The concern in the past was always shortening of lamp life, not the power used on starting. The CFLs I buy have lifetimes so short I'm not sure the duty cycle could have any impact.

 

[VEBill]

"The concern in the past was always shortening of lamp life, not the power used on starting."

All the arguments and urban legends that I've seen were about saveing power. Lamp life was the secondary consideration. The Mythbusters TV show addressed the issue in the same order (power, then life).

YMMV.

 

[dpc]

Trust me, back in the 1970s, no one was too worried about saving power. Lamp life was the prime concern. As much as I consider Mythbusters the ultimate font of knowledge in all things.

 

[VEBill]

LOL

 

[Fluorescence]

Thankyou all for these great replys,

DPC: "Wrong in what way? "

...i was thinking about the "pitting" of the cathode which supposedly happens at switch on, resulting in a reduction in its life-time, (and also meaning it becaomes more inefficient due to the pitted cathodes).

I thought lights that go on/off regularly would be better done with LEDs ?

 

[btrueblood]

"lights are extremely cheap compared to the cost of the power they use."

But the labor required to change bulbs isn't cheap...yet.

 

[dpc]

You have to state your priorities:

Initial cost
Energy use
Quality of illumination
Maintenance costs
Total cost of ownership

It's always some kind of compromise and the analysis always depends on some assumptions.

 

[IRstuff]

According to the Wikipedia article on CFLs, they need to be kept on for at least 15 minutes each time to achieve their nominal lifetime.

TTFN

FAQ731-376

 

[VEBill]

Wiki on wiki: "the ultimate font of knowledge in all things." ;-)

 

[MacGyverS2000]

<sigh> Wasn't there some initiative a couple of years back that was supposed to make people list (and back up) their credentials before posting/editing a wiki page? Right now, any monkey with a keyboard can post their best guess (or wives tale / urban legend), as proven often by the last wiki quote ;-)

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Morrand]

re: the Wikipedia, I don't think there was such an initiative (or if there was, it was dropped). They do require registration in order to do certain things, like create pages, but that's nowhere near the same thing as requiring credentials.

I'll say this much for it, anyway: it's a good source for general information, and when it's written correctly it's a good source for references to more reliable and detailed sources--but, yeah, it's really a bad idea to rely on it to prove much of anything. (For example, that same CFL article has some discussion attached to it that repeats the old "CFLs have poor power factor and are therefore inefficient" factoid that's been debunked elsewhere in these forums.)

 

[zappedagain]

Mac,

Some Wiki topics have a 'committee' that can reject changes to the page. I've heard of this on political pages and seen it on technical pages (the committee deleting mention of a company dealing in the subject; not quite plagiarism but close).