Light, whether natural or artificial, is a recurring motif. Natural light—such as the long days in Iceland, the sun, and the stars—symbolizes the conscious, rational world. Artificial light, such as the lanterns, is a stand-in for human knowledge and science and serves to create a fantastical, fairy-like atmosphere in the tunnels as it illuminates sights that are unknown and inaccessible to most people. When human knowledge first encounters new information, it seems magical until properly explained and categorized.

The absence of light beneath the ground symbolizes the irrational. Axel, for example, loses his ability to think logically when left alone in the dark. Such an interpretation highlights that the journey to the center of the Earth is also the attempt of the rational mind to explore and understand the subconscious.

A third type of light in the book serves to connect the artificial and natural—the light in the huge cavern created by the electricity in the air. It is closer in nature to the lantern light, but it is described as an “aurora borealis,” implying a natural phenomenon. Given the other dichotomies present in the novel, exploring the subterranean world can be seen as an attempt to reconcile the conscious and subconscious and the rational and irrational.