Equiloud shows how you can use a light source as a projector in C4D.
Lights in 3D can have properties that lights in real life miss. An example is that a negative value for a light typically will subtract light from an area. Another is the fact that you can use light in 3D as a kind of projector.
Check out this new tutorial from Uwe Schweer-Lambers, who shows how you can apply materials on lights in Cinema 4D to create some crazy effects.