Though many people (including some artists) never know it, not all shadows are the same. Knowing and understanding the differences between shadows and how to use each correctly will improve the quality of your artwork. I guarantee it.
|Gerrit van Honthorst, Supper Party, 1619|
Let’s begin by defining the two different types of shadows.
A cast shadow is a shadow that is formed when all or part of an object is blocking a light source. A cast shadow will always have a hard edge. This edge will soften as the shadow extends out from the object. The stronger the light source, the longer the shadow will remain hard edged. Cast shadows are always darkest at the base of the object and they become lighter as they extend outward.
A form shadow is a shadow that is created when the round edge of an object curves away from the light source. Form shadows will always have a soft edge. These shadows begin gradually as the side of an object (let’s say an apple) turns away from the light. Since light travels in straight lines from the source, it can not wrap around to light the back of the apple. So as this edge turns away, a shadow forms. This shadow will be darkest along the center edge of the apple.
Now that we’ve seen this explained in words, let’s look at a picture to understand what we’re talking about here.
|Edward Hopper, Lighthouse Hill, 1927|
In Lighthouse Hill, Hopper has provided us with examples of both form and cast shadows. The sides of the house, because they are straight and square, block the light from hitting the back of the house. Thus they create cast shadows.
The lighthouse, being round, creates a form shadow as it turns away from the light. Notice the soft edge of this shadow. However, the projecting edge at the top of the lighthouse (circled in red) is creating a cast shadow because it is blocking the light from hitting the side of the lighthouse.
This leaves one question unanswered. Why is the form shadow darkest in the center? This is the work of our good friend, reflected light. Think about this, we know that light only travels in straight lines. So logically all shadows should be completely dark since light will never curve into them. However, because light bounces off of everything it hits (some things more than others), it reflects back into the shadows.
Edward Hopper didn’t help us out too much here with reflected light, so let’s reference Honthorst’s Supper Party from above. Notice how the shadow on this face is darkest down the middle. This is because the light is coming from the right and reflecting off of other objects in the room and throwing some light back into the shadow on the left. Note that reflected light will always be darker than direct light!
Those of you who are particularly astute will also notice a cast shadow being formed by the nose. This is because the nose projects out from the face and blocks the light from hitting the eye. Take note of the difference in edges – hard for the cast shadow and soft for the form shadow.
A great exercise for understanding how to see and draw different types of shadows is to draw three eggs on a white surface. Look for where reflected light is hitting the eggs and where the darkest portion of the form shadow is. Practices like this, though they may not end up hanging on your walls, will greatly improve your future work. Again, I guarantee it.