I have been using cheap screw-in cfl bulbs to grow my chaeto in my sump and thought there had to be a better way. The light was not directional and is designed to light up a room, not a tank.
Old Bulbs
I had read about a DIY project years ago using Circular cfl screw in bulbs. Looking locally and on recent trip to the states, I could not find the 30 Watt adapter only 22 Watts.
In the end, I found them online - but i had to buy 6.
These take a 27w quad 4 pin bulb without any modifications. This one is 6500k and is available at all the big box hardware stores. I picked this up for $10 but i think they are about $14 at Rona.
If you don't put in the circular bulb, the 4 pin socket fits the 4 pins off the quad cfl bulb.
Each quad bulb is producing 1800 Lumens and is equivalent to a 100w incandescent (its even a bit more than 100W because it is overdriven slightly)
I am going to hook up 2 and have the equivalent to 200W. In addition to Chaeto, I'm going to put some frags under the light and expect that they will grow fine.
BTW, I've got a few extra Circline adapters that I am selling at cost - $5