Hi Kate,
I made a light box out of ply wood, lined it with white fablon cut a circular hole in the fron and fitted 4 lamps at the front behind the hole. I had a voltage variable control but you could also use a variable resister. Running on a 12 volt reglated transformer(Maplin) it was easy to adjust the flat ADU to about 30,000. Only problem you needed 2 people to a) hold it in front & b) take 16 flats. For the ALPY spectroscope the built in flat lamp is a easier option.