Darkness is the partial or total absence of light. In the Bible, it is symbolic of the total absence of the goodness of God, whom Scripture says is light and also dwells in unapproachable light, which no man can see or could ever see. Darkness has been used by God as one of His ten plagues against Egypt during the time of the Exodus, in order to get the Pharaoh to release his grip on the Israelites.

In the Left Behind series, the Fifth Bowl Judgment produced a plague of darkness occurring in a cylindrical area around the center of New Babylon in the last year of the Tribulation, only lifting a few days before the Glorious Appearing. From the outside, the phenomenon appears as an enormous dark column starting from the ground and going up into space.

Rather than affecting the physical movement of photons, the plague of darkness attacks the nervous system of all those within the affected area; aircraft radar and even the photocells on vending machines are shown to operate normally. Sound transmission is likewise not affected, indicating that sonar rangefinders would work.

Christians who bear the Seal of God would be able to see in what they describe to be sepia tones, up to roughly twenty feet (seven meters) out. Chang Wong and Otto Weser use this to their advantage to be able to move around New Babylon unimpeded, the former setting up remote systems so as to be able to control New Babylon's computers after escaping to Petra, the latter taking the opportunity to resupply along with his small underground church.

Unbelievers become entirely unable to process any form of light that reaches their eyes, perceiving absolute darkness with the exception of the body of Nicolae Carpathia, who can be seen as if he was glowing dimly, up to a similar distance. Unbelievers also demonstrate a form of blindsight, sufficient to let them find food and water if they are in a familiar environment. To escape the darkness, Nicolae had to walk in front of the caravan of cars that the Global Community leaders drove to the outer limits of the city in order to guide them.

People who are already completely blind would presumably be unaffected.

It is not known whether animals are affected.

Briefly before the Glorious Appearing, the area around Petra was plunged into darkness when Nicolae and the Unity Army made their charge against the believers hiding out in the ancient city, and the "sign of the Son of Man" disappeared from the sky, only that time all power and the ability to use firearms was affected on the Unity Army's side.