I thought I would share this info as I have started trying some new bulbs that have hit the market.
First off, I'd like to comment on the Panasonic EFD series of Compact Flourescent bulbs. These are screw in type bulbs for replacing standard incandescent bulbs (as many of you know, this is how I have set up my 22 gallon tank).
I noticed a few key features right away that set these bulbs apart from many others I have tried.
1.) Approved for totally enclosed fixtures
2.) The widest temperature range I have seen for bulbs of this type (-30C to +50C)
3.) High CRI (88)
4.) NICE colour (5000k, very bright white)
5.) High Lumen Count
6.) Most importantly, they fit into incandescent aquarium canopies with NO modifications!
I have purchased 2 different sizes of these bulbs to try them in different setups. The 14 watt bulbs are truly an incredible product. The integrated ballast is slender enough I was able to retrofit the 7.5 gallon tank http://www.plantedtank.net/forum/viewtopic.php?t=816
(a 5.5 gallon would be possible, and I believe the 5 gallon minibows from all glass would be ok) with these without any changes to the original hagen canopy.
The 23 watt bulbs were equally impressive, and fit in both 10 gallon and 20 gallon canopies while providing full light coverage of the tank.
The only downside to this series of bulb is the cost, roughly 1.5 times the cost of a cheaper bulb. Now, that being said, these bulbs last considereably longer because they are designed for high-heat situations.
If you want to retrofit that old canopy you have laying around, this is definately a bulb you should consider.