I have my sump in the dark so no algae grows, then I have a 26W (I think) 6500k plant compact fluorescent bulb over my fuge. Bout it at the indore sun show, and it is housed in one of those utility reflectors you can buy at lowes. Macro grows like crazy
I ran an 18w pc over my sump (roughly 30 gals) and was more than sufficient for the area it needed to cover which was roughly 1/3 of the sumps capacity.
I run a plain CF 20w bulb in an clip on fixture over the fuge. Chaeto seems okay with it. Total cost $0 (had the lamp from my son's old frog tank and the bulb was sent from PSE)
If you have any trouble with growth, you might need to buy an actual CF plant bulb. Those ones PSE sent out are 2,700k I think. You really want something closer to 6,500k for plant life.