I know people do flatfielding from the sky at dusk, but this has its own
problems. I know Olivier has shown how to use a quartz halogen flood
light for flatfielding. Besides quartz halogen, what other bulbs can be
used? What about the incandescent bulbs that have a clear glass? They
are usually called Crystal Clear. Is the gas inside the bulb a possible
problem that prevents one from getting a close approach to a black body
continuum? I think one advantage of these bulbs is that they have a
wider coverage than a quartz halogen flood light.

Just today I saw GE has a new bulb called a Reveal bulb. Robin, I saw
you made some comments about this bulb in the AAVSO discussion group but
am not sure if you were endorsing it or not. I am guessing there may be
problems with using this bulb for two reasons: a) it says "With Halogen"
which sort of implies it has something else that would detract from a
black body continuum, and b) the bulb glass has something in it called
Neodymium which filters out the "Dull Yellow Rays", as they describe it.
Hence, the spectrum would be stronger in the blue, it seems.
Stan