On Sat, 18 Aug 2007 20:34:56 +0100, "Newshound"
wrote:


In the case of CFL's I recall that while they do take more energy on
start-up, the break even point comes after a matter of a few seconds.
So, for practical purposes, they should be turned off when not
needed. With all of the ones I've seen, the bigger problem is what
was already noted. They take a couple mins to reach full output.
Even worse, the output is terrible for the first 30-60secs. For that
reason, I leave them on more than I would a regular light, thinking
I'll need it again in maybe 10 mins. But overall, I'm pretty sure
I'm saving a good bit on energy.

I don't think the startup energy is the issue, it is the wear and tear on
the lamp from thermal cycling which shortens the life.

It's not an issue of thermal cycling :

http://en.wikipedia.org/wiki/Fluorescent_lamp

It's during start up that most of the wear and tear is done to the
tube filaments. The filaments are coated with an emission mix which is
sputtered off causing blackening of the tube ends. When most of it has
gone the striking voltage of the tube rises until in the end stage the
tube will not strike any more. Some electronic ballasts can detect
this condition coming and shut down, other earlier/cheaper electronic
ballasts will continue to try to start the tube and end up being
damaged by overvoltage and fail. Simpler inductive ballasts with glow
switch starters do not fail but will typically run for months with the
tube flashing on but failing to start and then cyclically restarting
from scratch, this causes a nuisance and should not be allowed to
continue as eventually the starter can overheat melting it's mounting.

I leave a CFL on in a
(very dark) hall and landing all day, and they last years.