I am building a flourescent exposure unit using 24" bulbs. (F20T12/BL) I have seen several posts suggesting to use 40 watt bulbs vs. 20 watt bulbs. All I can find is 20 watt in 24". Do they make 40 watt bulbs in 24"? If so, does anyone know where to purchase them?
I have also seen suggestions to use high output bulbs. Is that the same as 40 watt?
Any suggestions on how close to install the bulbs under the glass?
Well, make sure you're using the correct lights. Not just any fluorescent will work (well, they might, but not efficiently).
You need unfiltered black light. Not the party lights, but the ones used for indoor green houses. You can get them from grainer.com the model is F40DX Daylight. Those are 40 watt. But most stores that sell planting supplies should have something similar.
If you already knew that, sorry.
Anyways, the wattage shouldn't be a problem, you'll just need to adjust your exposure time accordingly. And according to Fresner's book, the top of the lights should be no more than 3-4 inches away from the glass.
bro, ...i just built a 1000 watt metal halide
unit for less then $200.00
and now burn screens in 60 seconds...for real
look up metal halide in the search and follow the
plan....well worth it!!!!
The bulbs you bought are fine. My first blacklight exposure unit was with the 20w bulbs. I made a larger unit using the 40w bulbs, and bought Starfire low-iron glass for it, and truthfully, my exposure times are about the same.
A metal halide rig would be better, but more important is to make a vacuum frame lid to suck that screen down tight against the film.
One of the nice things about the fluorescent exposure units is you can use a darkroom timer, so you don't have to stand there and throw the switch off to shut off the light. That, and the film and emulsion don't get hot.
Thanks for your posts. It sounds like the 20 watt bulbs will do the trick. I'd love a metal halide unit, but for what I'm doing right now, I think the black light flourescent box will work for me. I'm currently using a 500 watt halogen with good results, but the 15 minutes per screen are killing me. And the halogen gets too hot.
Any thoughts on how close from the glass the bulbs should be? Is there such a thing as getting them too close to the glass?
Thanks for your posts. It sounds like the 20 watt bulbs will do the trick. I'd love a metal halide unit, but for what I'm doing right now, I think the black light flourescent box will work for me. I'm currently using a 500 watt halogen with good results, but the 15 minutes per screen are killing me. And the halogen gets too hot.
That was exactly why I switched to the fluorescents. Big difference in exposure time (much less) and heat (none).
Any thoughts on how close from the glass the bulbs should be? Is there such a thing as getting them too close to the glass?
I have mine about 3" or a little less away from the bottom of the glass.
I'm in the process of moving out of the garage and into a warehouse with a small office, so I'll really have room to strew my mess! I plan on reworking my large exposure unit into a metal halide, as I've got a 400w unit I bought off of ebay, as soon as I figure out the best way to minimize the heat from the lamp. That said, if things keep picking up after I'm settled in, my next major purchase will be a NuArc metal halide exposure unit, and I'll go back to using dual-cure emulsions for the resolution improvement.
Home built exposure unit questions 
