But what about when lit from the back?
This didn't look quite right to me because leaves are translucent; and here we should be seeing light coming through the leaves. I went out to a park to take some reference pictures of real leaf translucency:
So what dermines how much light we see filtering through the back of a leaf? One factor is how close the leaf is to the image of the sun. Another factor is the angle between the leaf and the sun. The final factor is the translucency of each part of the leaf. Here is a picture showing these three components:
When they are all combined, we get a correctly lit tree!
What do you think of our leaf translucency? Are there any ways that we could improve it?