How To: Add Volumetric Lighting
Cycles 4D makes this very simple by using the cyEnvironment object. Here is a simple scene illuminated without volumetric lighting. A single spotlight is used to light the sphere:
And now with volumetric lighting:
The only difference is the material applied to the cyEnvironment object. Here is the extremely simple node tree:
As you can see, all that is needed is to link a Volume Scatter shader to the Output node and (in this case) turn down the density. The higher the density, the less light will reach the object so you need either to turn this down or increase the light strength.
That's all you need to do to get volumetric lighting.