I'm currently using screw in spiral cf over my 20 gallon. I have had moderate success with microswords, dwarfsags, amazon, xingu and a few other plants.
Right now, I'm switching between two 26w full spectrums and two 42w 2700k. The yellowish color actually isn't too bad. I was able to get them for $1 as a pricematch to Stop and Shop's Earth Day sale, they're normally $9.
They're in a reflected clamp light right now. I know it is not scientific, but compared to the stock 15 fluorescent that came with the tank, they are about 10 times brighter.
In the next few days, I'm going to make a DIY canopy with it to incorporate all 4 bulbs sideways with reflectors. So I should have a base of 136w. If I am lucky to get 40%, I'll be around 55 watts.
Some people say the % is as little as 20-25, I personally think it is more than that. I think that with the right bulb, reflectors and canopy, 50-65% is doable.
I know the microswords are a medium to high light, and so far over the month and a half I have had them, I have noticed some new growth on them.
So I think an actual percentage is tough to come by. My only advice is to try it out and see. I hope to have a full report on my experiences with cf spirals in a few weeks.
Part of the fun of this hobby is trying new stuff, discovery and invention. What makes it fun and exciting is the constant struggle to make things perfect (and for some of us as near perfect on a tight budget).
