Inspired by Marco Bucci's teaching of keeping the light and shadow family separated in painting.
I think I have done this before, but this one might be the better answer to handle lighter/darker local value of an object.
Moo-ing horse
1. This is where I put one light source to illuminate the box with 3 different local value.
2. Separating the plane's value.
3. Connecting them to the full range of value.
4. Identifying the value from each object.
5. Light and shadow family found!
CONcluSION