Describing the depths or boundaries of darkness is something that is used a lot in narrative. The most interesting thing about darkness, from a storytelling perspective, is that it can be used to convey so many different things. While on one hand, that’s a no-brainer, it’s also something we love to read or see (as in movies) during a storytelling, so while it shouldn’t be overdone so that it’s obvious, it can still be an important vehicle for getting across larger, perhaps more literary concepts.
Darkness can evoke fear. There are monsters, demons, etc. that lurk in the dark. And though Hell is overtaken by flames, which should theoretically throw bursts of light into the environment, we still see an overwhelming, smothering darkness when Hell is portrayed.
Darkness can emit peacefulness. Quite to the contrary of evoking fear, a nice still darkness can bring a sense of peace. Where there’s nothing to see, there’s no crazy world moving around you at 100 miles an hour—that in itself can be peaceful. Then there’s the more paranormal feeling of peaceful darkness, where there is light but also an easygoing, serene darkness.
Darkness can represent vastness. Space is vast, but it’s also very dark, representing the great unknown. There’s no telling how far the darkness spreads or if it even ends—but there are stars and planets throughout the vastness, so it doesn’t really matter if it goes on forever or eventually ends. The idea remains, however, that there’s much more than anyone can imagine.
Darkness can represent emptiness. Again to the contrary, just as darkness can represent vastness, it can reflect emptiness. To take another space analogy, just look at a black hole. In reality, a black hole is nothing—the only way we know of its existence is by all the stars that surround it, being pushed out of the vacuous black hole and forced to surround, rather than enter, it. Within the black hole itself, however, is nothing.
Mood in stories is so important, and while it is possible to overdo the dark versus light descriptions, when done right, they can be powerful tools in the realm of storytelling.