Q: As a child 30 years ago, I was told that it was good practice to leave fluorescent tubes switched on rather than using them intermittently over short periods. I thought that this was because each time they were switched on, their life was reduced. Was this ever true, and if so, does it apply to the newer generation of tubes and bulbs? Is there an optimum time below which the light should be left on?
A: The reduced life of fluorescent tubes caused by switching is a minor factor. Information provided by my local electricity supplier states that 鈥淎bout one hour of life is used at each switching. When equating the cost of lamp life lost against the running cost we get a break even time of about 10 minutes.鈥�
I think it is important to note that there is a general misunderstanding about this issue. Many people believe that fluorescent tubes consume much more energy at start up than during running and use this as an excuse to leave them on all the time. This fallacy has been promoted in 鈥済reen鈥� literature in which people are told that switching on consumes lots of energy and that running consumes very little. This is not true and I have conducted my own measurements. The rule is that if you will be out of the room for more than ten minutes, turn the lamp off.
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