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Ask Cam

Fluorescents: Leave 'em on or switch 'em off?

August 3, 2010

Question:

Hey Cam,

A bunch of us were sitting around the other day, thinking of ways CSU could save money. We're wondering if turning off fluorescent lights actually saves money. We heard it costs more in energy to turn them on rather than leaving them on all day. Can you shed some light on this? Thanks!

Cam's answer:

I get a tingle from my horns to my hoofs whenever someone asks about ways to not only conserve energy, but save some coin at the same time!

To answer this one, I went to CSU Facilities energy engineer - and our campus’ conservation guru - Carol Dollard. This is what Carol had to say:

This is a myth that has persisted for years (decades?). It is generally not true. Fluorescent lights do require a small amount of extra "startup current" to turn on, but the TV show Mythbusters tackled this myth and determined the effect lasted fractions of a second so really did not have an impact on the economics of turning lights on and off.

What is affected is the lamp life. Switching lights more frequently shortens the life of the lamp. On the other hand, when the lamp is off, it is not using power, so there is a savings with switching lamps as well. So how do you know when to turn them off or not? It is dependent on local power rates and what you pay for lamps, but around here the break-even point is about 15 minutes.

  • So if you're going to be gone from your office for just a few minutes (to make a copy, for example), leave your light on.
  • If you are going to be gone longer (for a meeting, lunch, etc.), then turn them off.

So there you have it. You can find more conservation tips at CSU Facilities Management's sustainability page.

Here's to banking that energy!

Cam the Ram