But there may be a hidden catch.

As you tilt the roof , you reposition the view to get the full picture again.

Ahaaaaa; but this repositioning, to re-center the image also changes the lights origin.

 But is is an infinite light! So it should not matter. So to answer your question, yes it is one infinite light. And should not light them at all.................... (with the horizontal roof, that is)
With the horizontal floor an roof, in theory, only reflections would count.

By repositioning, your eye is looking at a different angle . . . that is all.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!