simple study

This is not exactly right, learn a few stuff when doing this.
gradient of light occur in all the 3 plane cause by the main light source and bounce lights.
Cast shadow is not relative to the value of cube but depend on the light source. Strong light = hard edge, soft light = soft edge, bright light= dark shadow, dim light = lighter shadow. Edge of shadow get softer as it go further away form the object that cast the shadow. Ambient occlusion occur when the object touches another object/ surfaces.