If light symbolizes God, darkness connotes everything that is anti-God: the wicked ( Prov 2:13-14 ; 1 Thess 5:4-7 ), judgment ( Exod 10:21 ; Matt 25:30 ), and death ( Psalm 88:12 ). Salvation brings light to those in darkness ( Isa 9:2 ). Although darkness is opaque to man, it is transparent to God ( Psalm 139:12 ).

Darkness is vital to humans, animals and plants. It maintains the natural circadian rhythm, so you know when it is night and when it is day. Most animals are much more sensitive than humans and can even sense light that is indistinguishable to the human eye.