I want one spot light only in the scene. But when I activate spot light to a plane there seems to be no difference in the lighting at all no matter how much power I add or any other changes. Do I have to be inside of a box to turn the sun off?
Thanks
Assuming I'm understanding what you are trying to do....
In the Environment tab, under "Adjustments", set the brightness to zero. That will turn off all the environment (world) lighting and leave only your one spotlight to provide illumination.
Add a ground plane, turn the environment brightness to zero, enable global illumination and that should brighten your day or scene.