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.

AIUI this old advice was based on an elementary error, as it
overloooked the fact that although the tubes may last more hours if
left on, they will in fact last less days.

This whole subject is filled with myth and bad advice. Today for
domestic installs, the only sensible thing to do is turn off when not
wanted, however long or short that may be.


NT