Adjust the penumbra radius manipulator to change how the brightness of a spot light beam decreases only near the edge of the beam. Only the spot light includes this option.
To show the manipulator, see Display > Show > Light Manipulators. See Show, hide, or resize a light manipulator.
You can display multiple decay regions for the penumbra, and adjust the penumbra angle interactively. To enable this behavior, open the Preferences window, and under the Manipulators category, Light Manipulator section, enable Show Decay Regions for Penumbra.
Penumbra regions are displayed with dotted lines, while the cone angles are displayed with solid lines. Move the penumbra radius manipulator to adjust the angle interactively.
