I've been restoring some old microscopes for a local educational nonprofit group and ran into a couple B&L scopes that used 15W incandescent bulbs in the illuminators. One was burned out and I couldn't find a replacement so I designed an LED holder that screws into the E26 bulb socket and wired in a 5 mm white LED. Powered by a 6V wall wart.
The original stuff:
The printed parts:
The result:
More details here.
Yes, a single 20 mA, 5mm, white LED provides plenty of light even at 400x magnification.
Ultra MegaMax Dominator 3D printer: [
drmrehorst.blogspot.com]