Typically, this area will be a plane turned toward us. The illuminated side turns from the light, into the darkened plane facing you. All these factors work in concert to create the core of the shadow. Reflected light acts as illumination from non-primary light sources. Reflected light influences color or lightness level on all parts of the form, but its influence is most evident in the shade zone.
Reflective surfaces illuminate nearby forms, even if weakly.
As light sources, reflective surfaces cannot illuminate as strongly as the primary light source. The sky can be thought of as a reflective medium. Photograph of lamp mounted to ceiling, illuminating white plastic sheet. Cave Extreme recessions where, due to a closed configuration, light is prevented from reflecting back to your eye. Cast Shadow Light rays travel in a straight-line path out from the source.