One big plus using even white LED would be that most of the wattage is wasted heating up and using the IR and red end of the spectrum, just to obtain the green/blue wavelengths, so the full spectrum output of the LED will provide a much brighter source up there with much less wattage/heat...

You did the right thing blacking out the inside lamp housing as the condenser just wants to see the even bulb surface at exactly the right height to focus to the condenser, but bright outer light can focus differently and cause outer ring, "kidney bean" effects, etc in the illumination field...

Underexpose a piece of photo paper from a set up/focused enlarger without a neg to see how even it is...

Steve K