Light vs. Dark

In Part I of Joseph Conrad’s Heart of Darkness, Marlow tells the story of his experience of going to Africa. Throughout his own narrative, Marlow often incorporates the contrast between light and dark. Some examples are “A lot of people, mostly black and naked, moved about like ants . . . A blinding sunlight drowned all this . . .” (15), “ . . . the brass-wire set into the depths of darkness and in return came a precious trickle of ivory” (18), and “The edge of a colossal jungle so dark green as to be almost black, fringed with white surf, ran straight, like a ruled line, far far away along a blue sea whose glitter was blurred by a creeping mist” (13). What does the contrast Conrad sets up in Heart of Darkness do for the reader? Does he use this as a racial contrast? Or did Conrad have something else in mind?