Much of Heart of Darkness is concerned with Marlow’s struggle to maintain his sense of morality as power conspiracies rage all around him and the mysterious figure of Kurtz piques his curiosity. Marlow’s desire to do good grows increasingly futile as he is plunged into a world where no absolute goodness exists and the best he can do is choose between a selection of nightmares. Eventually, we see that the characters become unable to distinguish between good and evil. Conrad illustrates this moral ambiguity with light and darkness imagery that often blends together, yet is imbued with an overall inevitably sinister shade.
Conrad’s use of light and dark imagery works on several different levels – the physical, the psychological, the racial, and the moral.
Conrad often uses light, not as a symbol for goodness or enlightenment, but as a foil to a darkness that it eventually collapses into and is tainted by.