you are right on about some flourscent bulbs looking dim to the eye but still providing a bunch og energy to plants. GE makes two plant bulbs. the popular GE P&A bulb is usually a "wide spectrum" (it says so by the label on the bulb) version one that emits more visible light, but they have another "narrow spectrum" that looks really really dim. almost like a pinkish purple black-light.
one important thing to note though: while there is not a direct correlation between light intensity and photosynthesis (if the light is intense but at the wrong part of the spectrum), the more intense the light, the better it is at penetrating the water, so while the GE wide and narrow spectrum bulbs might grow plants equally well in air, the wide spectrum will be better at penetrating to the bottom of the tank
90g planted tank & 55 g planted tank/sump, with opposing 12 hr photoperiods.
Filter: DIY rapid sand filter w/ 5 liters Eheim effisubstrat and 50 pounds of corse filter sand, 600 gph pump. dump returns.
Substrate: Gravel and laterite substrates, capped with Flourite and home depot sand.
Lighting: 6.7 watts/gallon on top
(2x175) of 10,000k MH, (2x128) ODNO GE P&A
3 watts/gal on bottom
(4x40) triton t-8 flourscent
Fertilization: Seachem liquid fertilization (iron and comprehensive), Tetra initial sticks
CO2: DIY 14 liter yeast (seven bottles connected to a gang valve)
400 gph reactor (gravel vacuum tube filled with bio-bale and a powerhead on top)