There are so many different kinds of mercury vapor to get into it. No reason to plow new ground here. If you are looking for a cheap source for alt process, use the sun. If you want to build a source, read the article at unblinkingeye.
Heat lamps are indeed the wrong end of the spectrum and for most Alt processes, you want to avoid excessive heat as it can cause fogging on the print.
If you do use bulbs, 24" 20 watt fluorescent with the designation of
F20T12/350BL. Make sure it is labeled BL and not BLB BLB tend to be more expensive and put out less UV.
This is from a book called Coming into Focus:step by step guide to alt photo printing processes.
Palladio Company. 800-628-9618. Palladium paper, light iunits and vacuum frames. Primarily phone and catalog orders. www.bostick-sullivan.com