The Cucoloris is used to create shadow patterns on backgrounds or subjects. A flatly lit wall can be broken up into interesting pools of light and shadow. Lighting directors frequently use them to simulate sunlight filtering through trees.
The 18x24" Cello Cucoloris from Matthews projects a more subtle pattern. The pattern itself depends on the distance of the light source and the distance to the background. This "cookie" has webbing on three sides to prevent injury and present a more finished look.