I once read a study by, I think, RCA, about rated life of filaments and
repeated switching off and on.  It concluded that one on/off cycle was
equivalent to about 20 minutes per filament off the rated life.

For example, an incandescent light bulb with an average lifetime of only
1000 hours.  If you take a large number of them and switch them on/off
1000 times, the lifetime drops to 600-700 hours (666.6 hours nominally).

They pointed out that fluorescent lamps have two filaments (40 minutes
per on/off from a lifetime of, say, 15,000 hours), and tube radios or TVs
could have over 20 filaments.  The main cost of switching lights in an
office building was paying the electrician overtime to do the switching.

The typical colour monitor probably has three filaments (although some
reduce the mean time between failure by doing it with only one filament).
From this point of view, it's a toss-up whether you should leave it on
when you go to lunch, but you would be better off to switch it off
overnight.

Of course, other things such as the cost of the electricity used enter
into what you choose.  For example, if you unplug it, it is even less
likely to cause a fire because it was "hit by lightning".

Boyd Ramsay

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