The atmosphere feature can be used to model the interaction of light with particles in the air. Beams of light will become visible and objects will cast shadows into the fog or dust that's filling the air. The atmosphere model used in POV-Ray assumes a constant particle density everywhere except solid objects. We want to create a simple scene to explain how the atmosphere feature works and how you'll get good results. Imagine a simple room with a window.
Light falls through the window and is scattered by the dust particles in the air.
You'll see beams of light coming from the window and shining on the floor. We want to model this scene step by step. The following examples start with the room, the window and a spotlight somewhere outside the room. The empty room we want to start with. The point light source is used to illuminate the room from inside without any interaction with the atmosphere.