I found a
chart online; great reference if it is correct (I have no reason not to believe it)
13 watt CFL produces 850 lumen
18 watt CFl produces 1100 lumen
23 watt CFL produces 1600
Based on this run a 23, 13 then 18 for efficiency of lumens per watt. So at 1 watt per gallon that is somewhere between 61 and 69 lumens per gallon.
Now the problem with low power LEDs is that they are listed in MCD which apparently does not have a direct ratio to Lumens, but let me go see what I can find.