When reproducing shadows cast by objects on each other, remember that sharp shadows are caused by a point source while soft shadows are the result of some extended or diffuse light source. This means that the light rays travel from that point outward in all directions. A distributed-ray source has the lights coming from an object larger than a single point, such as a desk lamp with a long fluorescent bulb or as a bank of lights. In this case, the light rays are more parallel. A parallel-ray source is so far away that all the light rays are parallel, such as the light rays from the sun.
Ambient light comes from a diffuse, nondirectional source of light.
It is the product of multiple reflections from the many surfaces present in the scene. A diffuse light comes from all directions. This is especially true of a scene with a great deal of reflected light. The term achromatic implies the absence of color. Thus, the quantity of the light is the only attribute.