Night or nighttime (also spelled night-time or night time) is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. The exact time when night begins and ends (equally true with evening) depends on the location and varies throughout the year. When night is considered as a period that follows evening, it is usually considered to start around 8 pm and to last to about 4 am.

Visual perception is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. This is different from visual acuity, which refers to how clearly a person sees (for example "20/20 vision"). A person can have problems with visual perceptual processing even if they have 20/20 vision.