MeshFogMaterial
Works only with "Renderer"->"PathTracing" in Graphics3D
defines a material for volumetric fog effect in MeshMaterial
MeshFogMaterial[density_:0.01]Enable "MultipleImportanceSampling"
Example
Define a sphere-fog and place a SpotLight to light it up from below
Graphics3D[{
{MeshMaterial[MeshFogMaterial[0.1]], Sphere[{0,0,0},5]}, {Red, Sphere[{0,0,0}, 1]}, {SpotLight[White, -{5,5,5}]}
}, "Renderer"->"PathTracing", Background->Black, "Lighting"->None, "MultipleImportanceSampling"->True]