The Fifth Vial
Darkness
Revelation 16:10-11

"And the Fifth Angel poured out his Vial upon the seat (throne) of the Beast: and his kingdom was full of darkness; and they gnawed their tongues for pain and blasphemed the God of Heaven because of their pain and their sores and repented not of their deeds."

           This is a repetition of the Ninth Egyptian Plague, that of the darkness.  The prophet Joel spoke of this day, "A day of darkness and gloominess, a day of clouds and thick darkness."