Quote Originally Posted by Vaughn View Post
...my exposure under a 750W Merc Vapor bulb is about 90 minutes ... Howard's is 6 minutes under a 1000W "multi spectrum" lamp
Graphic arts metal halide arc lamps are specific to the type of material being exposed. Using the wrong lamp can result in long exposure times. The metal halide HID lamps for graphic arts/UV curing have special dopants added to produce light at wavelengths that are optimum for a particular material. Iron-doped lamps emit heavily in the 350-400nM spectrum and may be a good match to dichromated gelatine which responds best to 360-375nM. Indium and gallium doped HID lamps produce most of their output in the 400 - 450nM range and may not be a good choice.

If the mercury lamp you are using is made for general lighting then it is probably doped to produce most of its light in the visible spectrum and as little as possible in the UV.