hello,
I searched and looked through a bunch of threads, but there was no definite answer. Some posts stated that HPS bulbs wouldn't work at all. Other posts said that it just wasn't as effective as a Metal Halide Bulb.
If the HPS can work at all i'm ok with that as I'm using a regular 500W Halogen Exposure unit that came with my kit and I would think the HPS would at least be better than that. A neighbor just tossed all of their cabinets/cupboards from their house and they had a cabinet that seems to be just about a perfect size to turn into an exposure unit.
If the HPS can't be used at all I'll probably just try and create a Flourescent unit as I don't have a few hundred to blow on a Metal Halide with all the hardware right now.

I hope this thread doesn't seem like other threads, but there didn't seem to be a real answer when anyone asked about the HPS bulbs. I have a HPS set-up(I think it is a 300W, but i'd have to check) and I'd rather try to utilize it if possible so I Can save up money for an Epson printer combo. Then I can finally print up some solid Transparencies and hopefully toy around with halftones too.

-Scott Lewis
Silk Screen Expressions