This seems to be a piece of so-called common knowledge that has never made sense to me, because nobody has ever been able to explain how such an anti-intuitive fact got spread around.
Does it save power to leave your fluorescent lights on?
And if so, why do fluorescent lights have switches?
A manager at my last job reminded me of this alleged fact when I was turning off lights behind me in the building. “It saves power if you leave them on,” he said. “It takes a lot of power to initially light up the [blah blah] the ballast of the light, which [blah blah blah] electricity [blah blah] lots of money.”
“Where did you find this out?” I asked, eager to learn its origin at last.
“A representative came to a restaurant I worked at and explained it to the managers.”
“A representative of the restaurant?” I asked.
“No, he was from the Sylvania light bulb company,” he told me.
Ah, I thought–truth at last. A legend perpetuated by the light bulb manufacturers to save customers electricity at the cost of buying more bulbs? Or is there some truth to this, after all?
I forgot to mention that you shouldn’t turn off fluorescents frequently (nor any light for that matter), such as when you’re leaving a room for 15 minutes, as it does shorten their life, but in your “shutting down the office for the day” scenario, you were doing the right thing.
I’ll reaffirm DMC’s comment. Most literature on lights and energy savings suggest that a fluorescent needs to be off at least 15 minutes to be cost effective. I understand it to be for two reasons (1) FLFs do require a slightly extra surge of power to start up, and (2) each time you turn on a FLF, you shorten the lifespan of the tube.
We’ve got a big obnoxious fluorescent light in our kitchen and it is on almost all the time. The bummer is, it shines into the bedroom, which can be very annoying. But we’ve only changed the bulbs 1 or 2 times in 15 years. Sometimes when we turn it off it won’t turn back on right away. I tend to think it’s just a crappy light switch, though.
But wouldn’t the same hold true for incandescent lamps?
An incandescent bulb’s filament has extremely low resistance upon start up, thus there must be an initial current surge. And turning an incandescent bulb on and off expands/contracts the filament, thus reducing its life.
An incandescent bulb only has a small filament to charge and illuminate, a flourescent bulb has to charge a much larger volume of gas. It is common with an old bulb for it to be giving off plenty of light with no flicker or anything, but turn it off and it may not be able to turn back on again.
Some ultra-high effeciency flourescent bulbs will have drastically shorter lives if turned on and off. We had some of these installed as a test at work (in the $&#@& BATHROOMS of all places!) and due to people instictively turning off the lights as they left the bulbs only lasted a few weeks. They finally put regular flourescents back in and put the ultra-high effeciency ones where they belong, in the allways lit hallways and entry areas.