Quote Originally Posted by Monophoto
I was in a Pt/Pd workshop a couple of weeks ago with Tillman Crane. He recommends just leaving the box on throughout the printing session.
This makes a lot of sense to me for a workshop enviroment but in my own working conditions it would be a very big waste of energy to leave the tube bank on throughout a printing session. At 12 tubes X 40 watts each that turns out to be almost 500 watts, a fair amount of energy. And there really is no point in leavingthe tubes on all the time as far as exposure consistency is concerned, because tubes reach full output almost immediately on being turned on. Yes, turning them on and off will shorten the life of the tubes somwhat, but that is the only down side.

The spiral tubes put out a lot of UV light, especialy in the 27 watt size which is now available, but their major downside is that they do not reach full output until they have been on about a minute or so, as others have pointed out. So in this case it would make sense to leave them on for the duration of the printing session. A better procedure, however, would be to connect the sprial tubes to a light integrator.