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Even though it says 15W = 60W? It says the compact flourescent bulbs uses 15 watts but puts out 60 watts. Light output is 900 lumens.
Those bulbs are sold as replacements for incandescent bulbs, but are much more efficient, so for the same light, less wattage is needed. The 15 watt CFL bulb is supposed to give about as much light as a 60 watt incandescent bulb. But our "watts per gallon" criteria is based on fluorescent bulbs, or compact fluorescent bulbs, so the watts for that criteria is the actual wattage of the bulb, or 15 watts.

The problem is that the screw in spiral tube CFL bulbs are not very efficient compared to a straight fluorescent tube. Much of the light they give is blocked by the adjacent spiral of the tube. So a 15 watt screw in CFL isn't nearly as effective as a straight fluorescent tube. I am using 2 20 watt screw in CFL bulbs on my 10 gallon tank, and I get no more than low light intensity from them. That is 4 watts per gallon, but is only as effective as maybe 1.5 watts per gallon of straight tube bulbs.
 

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you know hoppy i built a hood bassed on your ten gallon design for my 29 gallon tank using four 25 watt cfl bulbs and a make shift high gloss white reflector made from flashing and i can see straight through my gravel and have actualy been able to grow all sorts of plants so i am very happy with the cfl bulbs
Yes, I realize that others have had good results with those bulbs. That is what is frustrating. It may only take small changes in the hood to make a big difference - more room between bulb and reflector, larger hood size, etc. And, I have even seen big differences in brightness of the bulbs between two of the same wattage, same manufacturer, same part number. My 10 gallon tank is jinxed.
 

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I have used the 6500K GE bulbs and let me tell you, they aren't that great for lighting...

I swapped the standard bulb in my Eclipse 5 with a 15 watt 6500K and all it grew were aglae and insufficient plant growth. Makes sense because all that white light is just parts of the spectrum that plants can't utilize well.. especially green. Aesthetically pleasing results, but better off using it as a supplement.
That's interesting! I had never considered that those bulbs might be producing most of their light at wave lengths that plants don't use. That could explain the really bad results I got with the bulbs. Since I plan to get rid of that tank very soon I won't be trying other bulbs, but at least I can now see where I might have been off track. And, that could explain why others had so much better "luck".
 
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