<< I've been using a fluorescent "grow" lamp for exposing gums, but am
not really pleased with the contrast or exposure time compared to real
sunlight. >>
If you have used the grow lamp, you must have a unit already, so I guess the
easiest way is to replace the grow lamp with a black light or black light blue
tubes (BL or BLB). I believe that for dichromated gum, BLB works better.
Exposure should be easy to test. As far as difference in contrast compared to
sunlight, unfortunately you have to adjust your mix and maybe even procedure
....
Dave