As far as exposure units, to me the king of all exposure lamps is the 8,000 watt from Olec, now sold by Douthitt.
It has incredible multi spectral light that can really expose emulsion to it's absolute strongest capability.
Nothing wrong with lower wattage units, just longer exposures.
Ballpark Times on a pure photopolymer emulsion Like Murakami Aquasol HVP on a 110 mesh.
8,000 watts: 30-45 seconds
5,000 watts: 50-80 seconds
1,000 watts: 2.5 - 3 minutes
Fluorescent tubes 8 - 18 minutes
Why the different times? for fluorescent tubes a lot depends on the manufacturer, the type of tube and the wattage of the tube, as well as age. Even two exactly the same units will expose at different times for the following reasons: Age of Bulb: the older the bulb the longer it will take to expose, newer ones will expose faster. That's why high end exposure units come with an integrator that measures lumens, not seconds, so that the screen receives the right amount of light for exposure.
What type of Bulb? Use original manufacturer's bulbs. They have more precious metals in metal halide lamps and last longer and have better multi spectral wavelength output. Also where your shop is located has a lot to do with exposure times. Low humidity areas like Phoenix AZ can expose far faster than the wet foggy climate of the beach in California or the tropics. The best way to look at a screen is you can easily make an image with underexposure but you can't make a strong screen, only a complete exposure up to but not at over exposure will create a strong screen to withstand difficult inks like discharge, HSA, or long run plastisol. Post exposure is the obvious fix or hardening, but is possible that important layers of emulsion were washed off during development on the inside of the screen that prevents stencil breakdown, or pinholes due to squeegee abrasion.
