Penumbra Angle
The penumbra angle element determines the penumbra angle of the active light cone, if the light in question is the spot light . The penumbra is the outer spot light cone. The inner part encloses the light cone angle . If the penumbra angle is smaller than the light cone angle, then a light cone without any penumbra is used. The penumbra angle is expressed in radians, the default setting being 0.