Darkness

Darkness was the absence of light. According to the Fourth Doctor and Leela, "In the dark, we are all invisible, and all blind." (AUDIO: Last of the Colophon)

Dark planets were worlds which received almost no light, but which were nevertheless capable of supporting life. (PROSE: The Dark Planet)

While darkness generally impaired vision, some people, with an ability for night vision, could see well in the dark. (PROSE: Halflife, Tragedy Day) Humans could evolve larger eyes to accommodate for complete lack of light, as they did once on a planet given light only once every thousand years. Plantlife on this planet also developed to grow rapidly, through photosynthesis, during this brief span of sunlight. (AUDIO: White Ghosts) Gallifreyans could also see far better in the dark than humans could. (PROSE: Lucifer Rising)

The Vashta Nerada, as creatures of shadow, thrived in the dark, while light could easily drive them away. (TV: Silence in the Library / Forest of the Dead, AUDIO: Day of the Vashta Nerada)