POV-Ray : Documentation : Atmospheric Media Interaction
  POV-Ray 3.6 Documentation Online View Light Fading Atmospheric Attenuation Atmospheric Media Interaction

By default light sources will interact with an atmosphere added to the scene. This behavior can be switched off by using media_interaction off inside the light source statement.

Note: in POV-Ray 3.0 this feature was turned off and on with the atmosphere keyword. Light Fading Atmospheric Attenuation

Copyright 2003-2021 Persistence of Vision Raytracer Pty. Ltd.