Having a variety and contrast of values can be a key aspects to a successful color rendering. The contrast of light and dark hues will distinguish one object from the next and show the shape of an object. In the rendering above, the light was coming from the front right side. The darkest value in the inside of the cabinet was on the right with a highlight on the front of the ball shape. In my rendering class, this line drawing was used as a practice activity focused on rendering contrast of value. Want to view the values in your own image? Make a copy of it in black & white. By taking out the color or hues, you have an opportunity to study how the values are working in your image.