The Volume Light tool window controls the position of the light in the volume window and the type of lighting used. The position of the light is either fixed in the radar world space or relative in eye space. World Space's origin is the center of the volume sampling square. In this mode, the light rotates with the model. Eye Space's origin is the current viewing position. The light does not rotate with the model. The Azimuth slider controls the azimuthal position of the light relative to its origin in the x/y plane. The Tilt slider controls the position of the light relative to the origin on the z-axis.
The Type slider controls the intensity of the shadowing generated by the light. When set to Diffuse, shadows are at their maximum. When set to Ambient, there are no shadows.