Another light Study

First just let me say that i know the anatomy on the drawing sucks hardcore! I just grabbed the first drawing i had sitting around and scanned it in. My focus during this exercise was to better understand lighting and how to use it to describe form. If any of you know any better exercises to learn lighting please share them with me! I would be most grateful. By the way, I just want to say thanks to AJ and Edgar for their help! Also Critiques on the lighting is most welcome.