I'll tell you an experience I had today...
I have just returned home from a xmas holiday of 7 days and took my forest dragons and my cham to be minded by my parents (other usual lizard sitter had prior engagements

), anyway, my dragons were in a smaller temporary enclosure so the reptisun's were closer than usual to the plants. To my amazement when I went to collect my guys today, the hibiscus were actually thriving, soo much more new folage and nice healthy growth....

The conclusion to the experiment is simply to place light closer to your plants....
I'll leave it to you guys to do the rest.
BTW, I started a thread on this topic a few months back, since then I added another 2x18w flouro grow lights especially for the plants, things are going great, BUT no where near as good as the light fitting being closer to the plants like I have just experienced today!
Cheers Scott.