Do I get you right: A light travels along those paths in a multipass frame?
Yes. You can see a set up where a spline light simulates the sunlight reflecting off a spot on the floor here.
I used the lowest res Kleig light for speed.
Paths with straight lines are not really ideal, the best path would be a completely random squiggle that still evenly covered the area.
It's moofuf's principle there ...
a long time ago I posted s similar image testing "fakeosity"...