How difficult did you find it to distinguish between light from the primary source and secondary reflected light
I’m not sure whether I have understood what is meant by this and if have seen it at all. Probably I should do some research on this topic, trying to find examples to be sure that I didn’t completely miss the point.
Addendum: After reading around secondary reflected light, as summarized in the post Drawing Skills: Secondary reflected light, I think I have recognized and drawn it in the tonal studies without too many difficulties.
How has awareness of light and shade affected your depiction of form?
I think it adds a lot more interest to the drawings. Becoming aware of the lighter and darker areas within a single colour, and integrating this into the drawing, supports the three-dimensionality illusion. In the tonal study of four objects, I tried to draw the hatching lines as if I were drawing on the objects’ surface, which seems to help giving them an appearance of volume.