Ulco, the trees are from the Xfrog Africa package: The big one on the left is the African Mahogany and the smaller ones are the Wild Peach with the spiky plants on the ground being the African Boxwood. The scene is washed out because of the high haze values I used to get some extra light bouncing under walls.
I certainly like the daylight version better myself, but couldn't resist giving a night version a quick try.
UponInfinity, GI is generally the way to go provided that there is a lightsource in your scene. In my night version there is no direct lightsource at all, so I used the Ambient Occlusion mode to bring light in. I set the strength on surfaces to 0.3 and the strength in the atmosphere to 0.