In article ,
RJH writes:
Can't quite think this through. Work has just fitted a 23W CFL in an
Anglepoise type desk lamp, replacing an 11W - I asked for a brighter bulb.

I've noticed that the shade gets very hot - maybe a little less than a
CH radiator. But still hotter than I would expect. I've also noticed
that the sticker inside seems to indicate CFL max 11W, and incandescent
max 60W.

I've pointed all this out to them, but the thinking seems to be that if
it's OK for 60W, then 23W will be fine, and they can't explain the 11W.

Is this about right? Work asked me to tell them if it gets worse - but
short of burning the building down, I'm not sure what sort of thing I
should be looking for.

Slow work day . . . :-)

A GLS filament lamp is designed to run at around 200C.
A CFL is designed to run the tube at around 100C, so max power rating
is less. The life of the electronics in the CFL is very temperature
dependant. In a well cooled/ventilated fitting, the tube will generally
reach full life and fail when the emission material is all lost from
the electrodes. When run hotter, the life of the electronic control
gear reduces - typically it halves for every 10C temperature rise, and
if run hot, the electronics will probably fail before the tube does.

So the only consequence is likely to be shorter life due to the
integral electronics failing earlier.

An LED flood lamp or spot lamp might be a better choice because a
lower power LED (less than half that of the CFL) will still get you
more light where you want it. LED's are even less able to
withstand high tempertures than CFL's, so its benefit derives from
being twice as efficient, and being natuarally directional without
spilling light where it's not wanted. CFL's are particularly
inefficient in lamps or fittings which direct the light, because
large omni-directional light sources and compact reflectors don't
work well together, so in this case the LED is going to be well
more than twice as efficient.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]