Objects block light rays from continuing along this path. Areas behind the light-blocking body will not be illuminated. These areas are said to have a shadow cast over them. The boundary of a cast shadow can be plotted by running a straight line from the light source to the edge of the light blocking form, down to the next surface. At the boundary of the shade zones, cast shadows have a different edge quality than halftones.
Cast shadows have penumbras.
Soon I will develop a section describing the nature of penumbras.