Darkness - online puzzles

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

Humans are unable to distinguish color in conditions of either high brightness or darkness. In conditions of insufficient light, perception is achromatic and ultimately, black.

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

Complete darkness is when the sun is more than 18 degrees below the horizon.