A surface's ambient color is multiplied by the intensity of the ambient source to give the total ambient light reflected from the surface. Directional sources are described by a direction alone, and are useful for modeling light sources that are effectively infinitely far away from the objects they illuminate. The direction need not be normalized. Point sources are defined as a single point in space. They produce shadows with sharp edges and are a good replacement for extended and other computationally expensive light sources.
Spotlights are useful for creating dramatic localized lighting effects.
They are defined by their position, the direction in which they are pointing, and the width of the beam of light they produce. If neither angle is given, they both are effectively set to 180 degrees. Extended sources are meant to model spherical light sources. If you do not specifically desire penumbrae in your image, use a point source instead. The shadows cast by extended sources are modeled by taking samples of the source at different locations on its surface.