12 inches away from your light seems awfully close, unless you're exposing hat press screens.
For a single-point light source, your light should be at minimum the diagonal dimension of your screen. Some say 1.5 times. The reason is to spread the light out evenly over a larger area and reduce hot spots in the middle of the image and fall-off near the edges. That might be why your times are so short to get an exposure. I've got a 1200w Amerigraph MH unit that measures by light units, but I can tell you I might get an exposure that short with a 305 mesh count, but more likely around 2 to 3 minutes with coarser mesh/thicker emulsion using QX-1.
For a single-point light source, your light should be at minimum the diagonal dimension of your screen. Some say 1.5 times. The reason is to spread the light out evenly over a larger area and reduce hot spots in the middle of the image and fall-off near the edges. That might be why your times are so short to get an exposure. I've got a 1200w Amerigraph MH unit that measures by light units, but I can tell you I might get an exposure that short with a 305 mesh count, but more likely around 2 to 3 minutes with coarser mesh/thicker emulsion using QX-1.
