Christ suffered three hours of darkness as symbol of being utterly cut off from his Father. Through the darkness of his suffering, he earned the right to become the Light of the World that gives light to those who sit in darkness. We already experience that light in part, and we anxiously await the return of Christ, to usher in the new heavens and the new earth, in which there will no longer be darkness.
2 But for you who fear my name, the sun of righteousness shall rise with healing in its wings. You shall go out leaping like calves from the stall.