Joseph Meehan wrote:
Andy Burns wrote:
On 18/08/2007 18:59, Marsbar wrote:

Switch on only when required. What made you think that switching a
fluorescent light on and off wasn't a good idea?

It was either a common misapprehension, or used to be different with
older tubes. I certainly remember an "order" going around school in
the early 70's to NOT switch off lights during break-times as it took
more electricity to re-start them, than to leave them on for 20
minutes.

Actually it was that the total cost was more to turn them off than
to leave them on for periods of about 20 minutes or less. The
largest factor was the cost of replacing the lamps because cycling
them reduced their life. Note those figures were based on commercial
applications and included the cost of the maintenance man doing the
replacement. This was one of the studies we took apart in my
statistics class while working on my economics degree.

I seem to recall, and emphasise seem, that Which back in the year dot
when I started to subscribe, then suggested that a tube was best left on
for 45 mins., if you were likely to re-enter that room. I still have
that habit, but have reduced it to about 15 - 20 minutes.