Nick

Have you considered that these low enrgy bulbs take quite a while to start up and reach full ouput. I use them around my house and it's typically 10-20 seconds for decent output & a minute or so for full output.

I started down the route of designing a 10x8 enlarger, the light source was the major area of concern, I opted for the tungsten halide lamps with built in reflectors as used in many enlargers, however an Ebay purchase made making my own redundant.

The light box on my DeVere 5108 still gives even light output when bulbs go down, you should investigate how these light boxes work, looking at it I reckon extremely easy to make your own version, larger or smaller as well.