I could expose a board I had to work out the exposure time, its
different for every lamp wattage and board type so you need to work it
out for your set up. I cut a board in half and removed the light proof
protective film on the copper side. I laid this on the artwork which I
had taped to the glass at one end. You don't need a red light in a totally dark
room or anything like that, just keep exposure to a minimum and don't
have direct sunlight on it. I just drew the blinds while I was working.
I marked off 8 roughly equal
divisions on a piece of opaque card and used this to create a test
strip. At one minute intervals I raised the lid and slid the card out
one division. This particular unit has a safety cut out which
extinguishes the light when you lift the lid so I didn't have to keep
switching it on and off. I used the kitchen clock to time it and ended
up with 8 strips exposed from 1 to 8 min. I developed the test strip
and established 3 to 4 min was about right.