Darkness

Darkness is the condition resulting from a lack of illumination, or an absence of visible light.

Human vision is unable to distinguish colors in conditions of very low luminance because the hue-sensitive photoreceptor cells on the retina are inactive when light levels are insufficient, in the range of visual perception referred to as scotopic vision.

The emotional response to darkness has led to metaphorical usages of the term in many cultures, often to convey feelings of unhappiness or forebording.

"Darkness" may also refer to night, which occurs when the Sun is more than 18° below the horizon. Provided by Wikipedia