Light is shallow; darkness is infinitely deep. Light is always bounded, it has boundaries. Darkness has no boundaries, it is unbounded. Light comes and goes; darkness always is. When there is light you cannot see it. When light is not there you can see it. But it is always there; you cannot cause it. Light has a cause. You burn the fire, you put on wood. When the wood is finished the light will be gone. It is caused, hence it is an effect. But darkness is not caused by anything, it is not an effect. It is uncaused eternity.