OMG, I'm so glad I found this thread. I switched out the wimpy 15 wt tube fixture with two cheap clamp lights with 23 watt bulbs and now my tank looks luminous!
I have a 26 gallon bowfront, and the 15 wt light wasn't penetrating deep enough for my plants. Now I'm hoping with this new set up my plants will flourish.
Thanks for this thread!