Energy saving or not? Does it really save energy to turn off light bulbs, TV's etc. when leaving a room?

I have heard the argument that turning lights etc. off and on actually uses more energy than just leaving them on if you are only going to be gone from the room for a few minutes. Is there any proof one way or the other? Or a "rule of thumb" to determine how long you should be gone before energy savings... show more I have heard the argument that turning lights etc. off and on actually uses more energy than just leaving them on if you are only going to be gone from the room for a few minutes. Is there any proof one way or the other? Or a "rule of thumb" to determine how long you should be gone before energy savings would be evident?
Also - what about frequently used computers? Which is more energy efficient - leaving them on stand-by or shutting down completely between uses?
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