Darkness (nonfiction)

Darkness, the polar opposite of brightness, is understood as a lack of illumination or an absence of visible light.

Human vision is unable to distinguish color in conditions of either high brightness or high darkness.[1] In conditions with insufficient light levels, color perception ranges from achromatic to ultimately black.

The emotional response to darkness has generated metaphorical usages of the term in many cultures.

Referring to a time of day, complete darkness occurs when the Sun is more than 18° below the horizon, without the effects of twilight on the night sky.

• Darkness @ Wikipedia

• The Deep Dark is an art installation that asks "why do we fear the dark?" @ Boing Boing