This shader simulates light scattered by a thin, uniform atmosphere. It produces shafts of light and volumetric shadows cast from geometric objects. It works with point, spot and area lights, but not with distant or skylights. This is a scene-wide volume shader (or an atmosphere shader in Arnold terms).
Increases/decreases the atmospheric volume density. The following images show the effect of altering the 'Density' setting.
The samples are distributed according to the volume density. More samples will refine the quality of the solution.
Henyey-Greenstein Anisotropy coefficient between -1 (full back-scatter) and 1 (full forward-scatter). The default is 0 for an isotropic medium, which scatters the light evenly in all directions, giving a uniform effect. Positive values bias the scattering effect forwards, in the direction of the light, while negative values bias the scattering backward, toward the light. Changing the eccentricity, therefore, means that you will get a different effect depending on whether the camera is looking toward the light or away from the light.
Note that values very close to 1.0 (above 0.95) or -1.0 (below -0.95) will produce scattering that is so directional that it will not be very visible from most angles (and what scattering you do see may be noisy), so such values are not recommended.
The attenuation parameter sets the rate at which the rays of light traveling through the scattering medium are extinguished and how much light coming from the background is blocked. A high value means that light will only travel a short distance through the volume, while a low value means that light will travel a long distance through the volume.
Controls the degree to which volume scattering affects diffuse GI rays.
A thin volumetric spotlight with a small cone angle
The density control is multiplied by this RGB value (so a blue value here means blue light is scattered).
It is also possible to map textures to this parameter in order to get interesting volumetric effects. The example below uses a 3d fractal texture to simulate a cloudy fog effect.
Fractal texture mapped to Color