I have a little one. From 35 mm to 13x18 cm. A frustrum of pyramid
on one end a glass holder for negative and on the other end a
printing frame. Between a fixed lens.
It working properly with silverchloride POP papers, but the
chromatcolloids are usually a few times faster.
The average exp. time with strong sunshine: about 1-2 hour(s).
Fox Talbot had a similar enlarger also. So it is an enough tested thing.
I never tried it with artifical light but perhaps it working with a
strong UV lamp. (E.g. mercury vapour lamp without protecting cover
- dangerous for eyes!)
Balint Flesch