This setting defines whether or not a light source should illuminate the hair. It’s also possible to exclude light sources from lighting hair.
Use this setting to define the type of shadow the hair should cast. The following options are available:
The hair will cast no shadows, regardless of any light source settings.
The hair will always cast soft shadows, regardless of any light source settings (Hair-specific shadow maps settings should still be adjusted using this menu). All settings, with the exception of Traced Width, apply to soft shadows.
Use this setting to define the shadow map’s overall shadow density (affects self-shadowing and shadows cast onto geometry).
Use this setting to define the shadow density of shadows cast onto non-hair scene objects. There is a correlation to the Density setting. If Density is set to 0, even a Cast Shadow value of 500% will not generate a cast shadow onto geometry.
Use this setting to define the radius within which shadow maps will be sampled, from which an average value can be ascertained. Simply put: The larger the sample size, the softer the shadow will be.