This is exactly what I do (I have 2 of the 2x54 watt Hagen Glo fixtures though) and it is enough light to grow BBA if you want. When all 4 bulbs are on it is bright! I now have my lights hung about 10" above the top of my standard 75 gallon. You could probably get away with just one fixture.
What if I did this.....what if I had two of these aquaticlife fixtures on my tank. I ran on for 4 hours, then the second one with all 4 bulbs running as a mid-day burst for a few hours, then later just had the last two lights running. How will this help with growth? Ill be injecting co2.