Go to home depot, find the GE fluorescent floodlights...the ones that look like old-school floodlights but have the swirly fluorescent inside of 'em. If you look carefully, they have one brand that even has the kelvin rating printed on the packaging (in teeny-tiny print, of course). Look for the 6500K lights, and you'll be good to go. My chaeto grows like mad under this light, and it's been on full time for 8 months now. Can't beat that!!
Oh yeah, I don't know if anyone else has noticed this....but does your chaeto grow faster when it's kept trimmed back?? Or is that just my imagination??