This method of the Direct3dRMLight Class sets the angle of the umbra cone.
public void setUmbra(float u);
u | The new umbra angle. This angle must be less than or equal to the angle of the penumbra. If you set the umbra angle to greater than the penumbra angle, the penumbra angle will be set equal to the umbra angle. |
By default, the initial umbra angle is 0.4 radians.