POV-Ray : Documentation : Projected_Through
  POV-Ray 3.6 Documentation Online View Looks_like Light Fading Projected_Through


  light_source {
    projected_through { OBJECT }

Projected_through can be used with any type of light source. Any object can be used, provided it has been declared before.
Projecting a light through an object can be thought of as the opposite of shadowing: only the light rays that hit the projected_through object will contribute to the scene.
This also works with area_lights, producing spots of light with soft edges.
Any objects between the light and the projected through object will not cast shadows for this light. Also any surface within the projected through object will not cast shadows.
Any textures or interiors on the object will be stripped and the object will not show up in the scene. Looks_like Light Fading

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