I built my own model of this room off the posted image and rendered it as I suggested above.

As you can see, with just one light, the results along the ceiling and sections of the room not in the light are not well lit.  However, I think it's fairly realistic and if you want more light, add lights to the scene that you would expect hanging from the ceiling like real lights (fixtures and everything).

I did reduce the blur diameter away from 100 though.  I used something much more along the lines of 35.

Indirect lighting set to 400.  Skylight set to 50.

You can see the blue of the sky on the floor (just like it should be).

-Kix