As the ray marches through the dust all light coming from any light sources is accumulated and scattered according to the dust type and the current dust density. Since this light accumulation includes a test for occlusion, other objects may cast shadows into the dust. The Henyey-Greenstein function needs the additional parameter eccentricity that is described in the section about atmosphere. This keyword only applies to dust type 5, the Henyey-Greenstein scattering. Emitting Emitting halos only emit light.
Every particle is a small light source that emits some light.
This light is not attenuated by the other particles because they are assumed to be very small. As the ray travels through the density field of an emitting halo the color of the particles in each volume element and their differential transparency is determined from the color map. These intensities are accumulated to get the total color of the density field. This total intensity is added to the light passing through the halo. The background light is attenuated by the total density of the halo.