Darkness is the absence of light, which can occur in various environments, such as during the night or in enclosed spaces. It is a natural phenomenon that affects visibility and can influence the behavior of living organisms. For example, many animals, like owls, are adapted to thrive in dark conditions. In addition to its physical properties, darkness can also have psychological effects on humans. It can evoke feelings of fear or uncertainty, as seen in common fears of the dark. However, darkness is also associated with rest and sleep, providing a necessary contrast to the brightness of day, which is essential for the circadian rhythm.