Where are the 500W to 2000W equivalent output LEDS that run off the mains? I'll pop one in my enlarger and check it out...
I was talking about additive with relatively narrow passbands, so unless you misspelled "one" instead of "three", you are talking about a different beast. You also seemed to miss the important words right after where you stopped the quote.
I would suggest around 20 to 100 watt LED units to replace the 500-2000 W range in an additive system. You need a transformer, though. A side effect is that you can easily build or buy a stabilized power supply to get predictable and even results.
See Ebay for cheap prices, or
www.satisled.com for wholesale.
I am not sure if very high power units are available in the exactly desired wavelengths, though.
Let me also remind that the original question was using LEDs. Answering with "halogens are better" is clearly incorrect, even though I admit that there still is some usage for them even in new designs. I would, however, use halogens primarily in illuminating "continuous wavelength" subjects, i.e. photographing natural objects. Printing, on the other hand, can benefit from NON-continuous spectrum. This is exactly the reason why some people have preferred additive systems (with sharp-cut filters) instead of CMY filtered white light sources; but the usually cited problems of additive systems are related to the problems of using incandescent light sources in them, making them big, heavy, high-power, low light output, with quickly wearing filters. These problems are now solved thanks to LEDs.
Times change and LEDs provide excellent
printing properties especially in
additive systems. An additive halogen system was claimed better than additive LED system which clearly can now be considered untrue in most cases because of the reasons I listed above.
And, if we come back to the original question of multigrade B&W; if the LEDs are selected correctly, all filters can be removed from the system, simplifying the optical path and increasing light output; and contrast grades will work simply with electronic control. I would suggest adding red for paper placement / focusing aid and for future color work even if the OP wouldn't do color right now.