Radiosity Test: How can I improve this?

I really have no experience whatsoever with radiosity, and I thought I’d try it out. I’m willing to wait for a bit longer rendertimes (it’s still quicker that indigo!). I just don’t have the hang of all the settings exactly; how to use them the most effectively. Here’s a quick test I did. How could I make the lighting more realistic?

P.s. I don’t understand the “Convergence” slider. I’ve looked it up in a few tutorials, but nothing seems to give a clear explanation…

Use more vertices. (Subsurf modifier with Simple Subsurf)

Convergence is the amount of light energy, that may remain unused in the scene (neither has vanised into infinity nor has been absorbed). So the smaller the convergence value, the longer the calculation time.