Now, i didn't do any calculations, I just used photoshop and created some parallel lines and perpendicular lines and came to the conclusion that if you wanted to reduce the light more you could just have a dangly bit at the bottom of the porch. Don't ask me if that is structurally cool or not, but it seems to me to significantly shrink the amount of light that would come in, which I believe to be the purpose of the task.
Edit: Oops i just noticed that it wasn't the porch above the window, it was the roof. That makes me less confused and makes my suggestion a little more lame.
