If it is the lamp house I am thinking of - similar to the Omegalite - it uses a circular household flourescent of the sort you might find in a kitchen ceiling lamp.
The warm up is like any other flourescent lamp. Takes a minute or so to get to full brightness. If you make sure the lamp is warmed up before you print things may be OK.
This lamphouse design is not used anymore because of this problem. The design does provide lots of very even light using a very low cost design, however.