The plague (the ninth) of darkness in Egypt (Ex. 10:21) is
described as darkness "which may be felt." It covered "all the
land of Egypt," so that "they saw not one another." It did not
extend to the land of Goshen (ver. 23).

When Jesus hung upon the cross (Matt. 27:45; Luke 23:44), from
the "sixth hour there was darkness over all the land unto the
ninth hour."

On Mount Sinai, Moses (Ex. 20:21) "drew near unto the thick
darkness where God was." This was the "thick cloud upon the
mount" in which Jehovah was when he spake unto Moses there. The
Lord dwelt in the cloud upon the mercy-seat (1 Kings 8:12), the
cloud of glory. When the psalmist (Ps. 97:2) describes the
inscrutable nature of God's workings among the sons of men, he
says, "Clouds and darkness are round about him." God dwells in
thick darkness.

Darkness (Isa. 13:9, 10; Matt. 24:29) also is a symbol of the
judgments that attend on the coming of the Lord. It is a symbol
of misery and adversity (Job 18:6; Ps. 107:10; Isa. 8:22; Ezek.
30:18). The "day of darkness" in Joel 2:2, caused by clouds of
locusts, is a symbol of the obscurity which overhangs all divine
proceedings. "Works of darkness" are impure actions (Eph. 5:11).
"Outer darkness" refers to the darkness of the streets in the
East, which are never lighted up by any public or private lamps
after nightfall, in contrast with the blaze of cheerful light in
the house. It is also a symbol of ignorance (Isa. 9:2; 60:2;
Matt. 6:23) and of death (Job 10:21; 17:13).