The Spot Fill tool works like the standard fill light control, but adds circular area control for finer control of the effect with on-screen adjustments for size and position.

Fill: Extent to which the Light Color is added to the scene.

Radius: Size of the area outside which the blur operation is at full strength.

Spread: Threshold/softening region feathers the radius.

Falloff: Sets the median point between the Radius and Spread.

Light Color: Color used to illuminate shadow areas.