Steve,

I had the same thought about making a light source from LEDs.

The idea is exiting, as you can get a small light source, vastly reduced heat , and the beauty of RGB LEDs, effectively giving you a full colour head or variable contrast, Green/Blue, for us B/W printers.

The main restriction so far is the limited output, even if you use some 5W LEDs.

I am trying to modify a Durst 138s to give more light than the standard 75/110/300W enlarging bulbs.
The 300W bulb produce about 5000 lumens, and I am unable to find the equivalent, let alone brighter output from LEDs.

Metal halides bulbs do give great output; 125 or 150W = 12500Lumens!
But you are back to using multigrade filters.

High power fluorescent coiled bulbs exist up to 85W, equivalent 500W tungsten, not enough lumens and the bulbs are nearly 300mm long, and impossible to accommodate.

Would really welcome input/help from anyone who has tried.

Danny