The interplay between light and dark become a key motif in the book, evening contributing to the title. The narrative is presented as a journey from light to dark, both in the sense of journeying from the “enlightened” Europe into the dark heart of Africa and journeying into the darkness of Kurtz’s character. This transition from light to dark is gradual and corrupting, affecting Marlow and changing him forever.

The lighting in the book is perpetually hazy. There are very few moments of pure light; instead, everything is cloaked in fog, mist, and darkness. In London, as Marlow and his companions sit on the Thames, a mist settles over the river and the sun begins to set. It is this fading light that inspires Marlow to tell the story of the time he confronted darkness in its purest form. Additionally, the Belgian city is described as gloomy and impervious. This reflects the characters’ willful ignorance of the truth about what is happening in Africa; Marlow’s aunt, for instance, will not be convinced that the colonial presence in the Congo is anything other than benevolent. Her ideas, like the city itself, is shrouded in an impervious fog that morality and truth struggle to penetrate.