For those interested in Wizzard~Of~Ozz's article, here's an Excel compatible (macro-free) spreadsheet
you can mess with that lets you combine different bulb types: say, 40w CF plus 20w T12.
In addition to lumens/sq in, it gives "Equiv T12 wpg" (Lumens/(Lumens/T12 watt * Tank gal). It also includes "Tong's WPG," which comes from (lumens/sq in)/(5.63 lumens sq in/1 WPG). (A standard 55gal aquarium with the average T12 bulb with an efficient reflector is 5.63 lumens/sq in.) The bulbs book has lumens/watt and it starts the conversions, in case you want to change it for a specific bulb.
Tong on AA has raised the point that short (say 24" and less) bulbs have less lumens/watt than the ~48" bulbs we did quick and dirty deviation on to obtain average lumens/watt. He explains this and other points in the fourth page of this thread
, offering another interesting reason why wpg breaks on small tanks. Eventually there'll be an updated calc and supporting bulb samples for this. Wizzard~Of~Ozz has a survey
linked in his article, and more entries from APC would be real cool to use as the standard to compare calcs/ideas to. Just saying.
To add two cents to John N.'s posts, screw-in CFs (for incandescent sockets) lose a lot of light due to, as I understand, "restrike." The parallel U-tube style above is theoretically better than the spiral bulb shape. IMO they still get destroyed by "true" CFs with lower total wattage. Here's some pics of various lighting over an 8gal for comparison. Here is 2*23w spiral screw-in CF inside a painted white hood 2*13w AHSupply Bright kit (their reflector)
(Light in the sump, 23w spiral screw in CF in a desklamp, is the same in both pics. Especially notice how much light hits the bottom of the comparison tank.) 20w T12 NO with bent metal as a reflector
. 2*13w AHSupply bright kit