How Shadows Are Formed An opaque object blocks the light falling on it. This creates an area of darkness on the side of the object away from the source of light. A translucent object also creates a faint area of darkness. An area of darkness formed by an opaque object obstructing light is called a shadow. The following three things are required for a shadow to form: 1. a source of light 2. an opaque object 3. a screen or surface behind the object.