'Darkness' in the Bible

The sun will be changed to darkness and the moon to blood, before the great and glorious day of the Lord comes.

And now behold, the hand of the Lord [is] against you, and you will be blind, not seeing the sun {for a while}. And immediately mist and darkness fell over him, and he was going around looking for [people] to lead [him] by the hand.

to open their eyes [so that they] may turn from darkness to light and from the power of Satan to God, [so that] they may receive forgiveness of sins and a share among those who are sanctified by faith in me.'