With the temperature increasing in the junction, the wavelength of the LED drift a bit and the light output decreases significantly.
Considering the narrow peaks of the paper sensitivity, this might be an issue. A large heat sink will solve this problem!
The stepper motor seems quite an overkill solution, but you could replace the filters easily if necessary (
filter wheel) which would be a great feature for experimenting. Note than a stepper motor + driver cost less than $50. you can also recycle a stepper motor and its belt from an old ink jet printer Check here for a
low cost driver. This would be very easy to make for an omega enlarger as you can easily replace the head.
If only the blue LED is a problem, there is also the option to add filters on your blue LEDs only (check the B370
http://www.hoyaoptics.com/color_filter/blue.htm) ?
This would be easy to do?
The ra-4 digital printer might use lasers.
Dominique
What is your enlarger