In article , bonnie wrote:
Given, CFL's are thought to be more energy efficient than incandescent
bulbs. But I heard they use more energy to turn on.

That is absolutely false. It is a continuation of an old myth that
fluorescents have some big surge in power consumption when they are
turned on, supposedly amounting to a significant amount of energy
consumption. That is simply not true.

That is a mistranslation from advice to leave fluorescents on rather
than turn them off and back on, unless they will be off for a substantial
amount of time - due to starting-related-wear.

What if it is in a room that is used infrequently, a closet or guest
room for instance. In other words a room in which you would go in and
out of pretty quickly.

How long would a CFL have to be left on to realize the net energy
savings.

This varies widely with lamp wattage, lamp cost, starting technology
used, and your electricity cost rate. I would say, as a
"one-size-fits-all" figure that is at best a ballpark, 5 minutes for
wattages at least 10 watts.

I consider closets, refrigerators and motion sensor lights to not be
candidates for CFLs.

There are cold cathode ones that do not experience starting-related
wear. However, they cost more, are less widely available, available only
in lower wattages mainly 8 watts and less, are less efficient than the
usual hot cathode ones, and still need to warm up to achieve full light
output. Cold cathode CFLs are best for frequent on-off use. They take
too long to achieve payback when they are off 98-99% of the time.

- Don Klipstein )