Darkness

Darkness is the absence or markedly reduced level of visible light, creating a condition in which surroundings are not illuminated. It is a perceptual and environmental state rather than a material substance, occurring naturally at night or during eclipses and can be produced by turning off lights or blocking light sources.

Light, the electromagnetic radiation within the visible spectrum, defines darkness by the absence of photons reaching an observer. Luminance is measured in lux; full daylight can reach tens of thousands of lux, typical indoor lighting is around 100–500 lux, and a moonless night may fall to about 0.001–0.1 lux. Absolute darkness outdoors is rare, while total darkness can occur in caves or during certain eclipses.

Perception and biology play a central role in darkness. The human eye relies on rods and cones; darkness shifts vision to rod-dominated scotopic processing, reducing color discrimination and enhancing sensitivity to movement. Adaptation to darkness takes minutes, during which brightness and detail improve.

Natural darkness arises from night, weather, and terrain that blocks light. Artificial darkness refers to intentional or incidental light control, notably light pollution and excessive artificial lighting, which can degrade night sky visibility and disrupt ecosystems and human circadian rhythms.

Culturally, darkness has long served as a symbol in religion, folklore, and literature, often linked to danger, the unknown, or rest. In science, darkness underpins studies of nocturnal biology, circadian rhythms, and astronomy, and it should be distinguished from dark matter, a separate concept in physics. Darkness is thus a contextual phenomenon that affects perception, biology, and culture.