It's fun to challenge yourself to simplify, let the light and value describe form. Hyon painted with me in this same park a little more than a week ago and she was talking about 'notan,' which to me means see in 3 values.
'Conversations in Paint' by Charles Dunn has a chapter on it with good illustrations and you can check out the short video below. My painting ended up a little more complicated but the underlying structure is there. Some one told me it looked like a very serene little house; I think its a direct result of the light-dark harmony. Have you ever worked with this Japanese design principal? It's just getting back to basics, especially if a piece just isn't coming together. Let me know if you try it :)