These (now not so new) low energy light bulbs are often marked up as "Not
for use with dimmers, timers or photocell controlled switches". I can
understand fairly intuitively why dimmers and photocell controlled switches
are excluded, but why should these bulbs not work with a switch that is a
My guess: some timer switches are electronic, rather than mechanical,
switches. The bulbs are not compatible with electronic switches. For the
manufacturer to cover their own arses, they say "don't use on any timer"
because they have to assume the average user is dumber than a blunt hammer
and won't know the difference in timer switches.
Charles Perry P.E.
A couple of issues. Firstly, a number of these special switches actually
power themselves through the filamant of a filament lamp, drawing a tiny
current even when the light is apparently off. This doesn't work with a
low energy lamp (it can cause the lamp to flash periodically and/or the
switch not to behave correctly, or even work at all). If the switch has
a separate neutral connection to power it and a relay to switch the load,
then it will work with a low energy lamp (even photocell switches -- I
have one such on my porch).
The second point is that low energy lamps generally don't like frequent
switching (reduces lamp life) and can take a minute or two to run up to
full brightness. This makes them unsuitable for short duration use such
as a 2 minute timed switched in a communal entrance or triggering via
a movement or occupancy sensor for a only a few minutes switch-on.
I had a electromechanical timer like this for my front porch light. It
worked fine with incandescent bulbs, but had mixed reactions to compact
fluorescent bulbs. Some CFs worked fine and some burned out after only
a few days. I finally solved the problem by buying a different timer,
electronic with its own AAA battery, that does not draw current through
Agreed. I have two such photocell switches on the lights on the rear
of my house and they work fine with CF floodlights. The CFs do call
for a "moisture protected" outdoor fixture, so I installed the
floodlight sockets with a wider section that covers most of the lamp -
not the common ones that only cover the socket. The bulbs usually last
a few years.
the low power floresents have an inductive load, (normal light bulb is
resistive) which dimmer and photo cell were not designed for, too much
current throuth the latter killing it eventually or oerheating it.