HRESULT SetPenumbra(D3DVALUE rvAngle);
Sets the angle of the penumbra cone.
·Returns D3DRM_OK if successful, or an error otherwise. For a list of possible return codes, see Direct3D Retained-Mode Return Values.
rvAngle
New penumbra angle. This angle must be greater than or equal to the angle of the umbra. If you try to set the penumbra angle to less than the umbra angle, the umbra angle will be set equal to the penumbra angle. The default value is 0.5 radians.