One of the guy's at one of my LFS always has told me, "Don't go by the WPG rule, you know what really matters is the lumens.." I agree with him that lumens is more important than watts. As pointed out by Giancarlo though, it is much easier to explain to someone WPG than have them looking around for lumens on each bulb packaging. I think lumens would extremely complicate the process of helping someone out when the are first getting into the hobby. One of the guys at my LFS was showing me that these T8 Hagen glo bulbs had really high lumens that could be close to that of what is is being outputted by some of the CF bulbs. I still use WPG though since it's easier..Simpte 27 said:So when talking about aquarium lighting for plant growth, would it be more accurate to measure lumens over watts?