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Chris, David -

neither of you seem to have bothered stating what you're assuming happens
*around* the flowerpot. And it seems from the side as if one of you thinks
it's "totally obvious" that the flowerpot is *instead* of the rockwool,
i.e. that the top and sides of the inverted flowerpot are open to the
surrounding air - in which case the lamp will indeed run a lot cooler,
since
the pot itself will be able to dissipate a fair proportion of the heat
produced by the lamp to the free air around it by both radiation and
convection. The other of you seems to assume the pot is covered/surrounded
by the rockwool, and under this assumption quite correctly points out that
once the air around the lamp and the pot have risen to pretty much the
temperature of the lamp fitting (which they will, since the surorunding
rockwool prevents nearly all the heat from going anywhere useful), the
temperature of the lamp under the pot under the rockwool will be no
different from the temperature of the lamp directly under rockwool.

Have I got the source of the divergent views right? (And will I regret
piping up at all? ;-)

Stefek

well I'm half way in between

the pot is in a hole in the insualtion but the top is not covered with
insulation.

cheers

David