Understanding how to use tonal values in paintings and photography is paramount to a successful outcome. This tonal value sphere is found in "Exploring Visual Design" by Joseph Gatto, Albert Porter, and Jack Selleck. Davis Publications 2000.
The highlight is where the light hits the sphere. Transitional light is the middle value between the light and dark. The core of the shadow is the area on the sphere that is the furthest from the light. The reflected light is the area that is reflecting the light from the table. And, the cast shadow is the shadow that the sphere is casting onto the table.
Due to the importance of learning to see value changes in art, my students paint a value painting in black and white before they paint in color. Also, something that a lot of people miss is adding that very dark line under an object. I call it, "Sitting an object down". Try putting an apple on a table and look directly at where the apple meets the table. It's almost pitch black, then the shadow extends from there.
I hope this helps you in your painting and photography journey! - Jill