Behavior of a shadow, photo 1 of 3..When a small (point) light source illuminates an object, it casts a shadow that is sharp and well defined (Photo 1). With an extended light source, whose size is comparable to the size of the object, the edges of the shadow are blurred (Photo 2). The larger the light source, the more blurred the shadow becomes (Photo 3). Here a chess knight is used to demonstrate the effect. Photo 1 of 3.