|MadSci Network: Engineering|
Excellent question! You have to look at it in two parts: a: the cost of the electricity alone b: the overall life cycle cost of the light that you're paying for. a: There's no question that turning the lights off immediately after leaving the room saves electricity. How many $ that saves depends on how much you're paying for electricity. But that's not the whole picture. b. When you cycle a fluorescent light on/off, you shorten the life of the bulb, starter, ballast. These cost money to replace, lost productivity while the fixture has failed, and labor costs to replace the bad parts. The numbers I've read vary, but it seems that if you're only going to leave the light off for anywhere from 30--90 minutes, depending on who you listen to, you're better off in total life cycle cost if you leave the light on. One company I worked at had the fluorescent lights turned on by infrared motion sensors in the room, and would leave the lights on for 45 minutes when the motion sensor was activated. This seems like a good idea, and obviously the company's calculations said that 45 minutes was the optimum number in terms of total life cycle cost. So your idea is validated in at least one real instance. One small point: a common spelling error is to spell it "flourescent". The correct spelling is "fluorescent". One caution: if you're at a party with engineers or science students and you mention this subject, an argument will invariably result. Of course, that might be interesting--your call. Good Luck!
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