Darkness is a key idea within Lord of the Flies. How does Golding use darkness in the novel?

Golding uses darkness in Lord of the Flies to further the action, the theme, and characterization. Since the boys are on a deserted island without adults, realistically they are bound to be frightened of the dark. They suddenly find themselves in a world without electric lights, and the darkness is darker than what they have been used to. Many of the worst things that happen to the boys occur in the darkness or as darkness approaches: The plane crashed in the dark; the fire that kills the boy with the birthmark happens at dusk; the boys have nightmares in the dark; Ralph loses control of the assembly because he calls it so late that the darkness allows talk of ghosts to take hold; the "beast from air" descends on the island at night; Simon is murdered in the dark; Piggy's glasses are stolen at night; and it is nighttime when Ralph learns from Samneric that Jack intends to kill him. 

Golding's theme of the darkness of the human heart follows along with his use of darkness in the narrative. Many of the worst displays of negligence, rebellion, and violence occur in the dark. During Ralph's last night alone on the island, he is tormented not just by the darkness of the night but also by the moral darkness the other boys have succumbed to. He remembers Piggy's fatal fall, and to him "Piggy was everywhere, was on this neck, was become terrible in darkness and death." 

Golding uses darkness to enhance characterization, especially of Simon. Interestingly, black-haired Simon seems to be the only boy who does not mind the dark. He finds a little thicket where he likes to go to be alone, even at night. There, in the darkness, "the candle-buds opened their wide flowers glimmering under the light that pricked down from the stars." Just as the night-blooming jasmine flowers (probably the flower Golding had in mind--see video link) bloom in the darkness, so Simon is able to retain his purity despite the depravity of the others. Even Ralph and Piggy end up partaking in murdering the innocent Simon. Only Simon in the novel is able to face the darkness of the Lord of the Flies, in his vision even entering inside the mouth where "there was blackness within, blackness that spread." He also faces the "beast from air," examining it until he understands what it is--a decomposing paratrooper--and setting it free from the parachute. Of all the boys, Simon can touch darkness without being tainted by it, perhaps because he alone understands "mankind's essential illness."