Darkness

Darkness, in contrast with brightness, is a relative absence of visible light. It is the appearance of black in a color space. When light is not present, rod and cone cells within the eye are not stimulated. This lack of stimulation means photoreceptor cells are unable to distinguish color frequency and wavelength. The resulting perception is achromatic and in the case of darkness, black. The emotional reaction to darkness has metaphorical importance in many cultures.

Scientific

A dark object absorbs photons, and therefore appears dim in comparison to other objects. For example, matte black paint does not reflect visible light and appears dark, but white paint reflects all visible light and appears bright.[1] For more information see color.
However light cannot simply be absorbed without limit. Energy, like visible light, cannot be created or destroyed. It can only be converted from one type of energy to another. Most objects that absorb visible light reemit it as infrared light.[2] So, although an object may appear dark, it is likely bright at a frequency that a human being cannot see. For more information see thermodynamics.
A dark area has limited light sources, making things hard to see. Exposure to alternating light and darkness (night and day) has caused several evolutionary adaptations to darkness. When a vertebrate, like a human, enters a dark area, its iris dilates, allowing more light to enter the eye and improving night vision. Also, the light detecting cells in the human eye (rods and cones) will regenerate more unbleached rhodopsin when adapting to darkness.
One scientific measure of darkness is the Bortle Dark-Sky Scale, which indicates the night sky's and stars' brightness at a particular location, and the observability of celestial objects at that location. (See also: Sky brightness)
[edit]Cultural



Separation of light and darkness, from the Sistine Chapel ceiling by Michelangelo
Further information: Light and darkness
[edit]Poetic
As a poetic term in the Western world, darkness can also mean the presence of shadows, evil, or depression.
Religious texts often use darkness to make a visual point. In the Bible, darkness was the second to last plague (Exodus 10:21) and the location of “weeping and gnashing of teeth.” (Matthew 8:12)[3] The Qur’an has been interpreted to say that those who transgress the bounds of what is right are doomed to “burning despair and ice-cold darkness.” (Nab 78.25)[4]
In Chinese philosophy Yin is the feminine part of the Taijitu and is represented by a dark lobe.
The use of darkness as a rhetorical device has a long standing tradition. Shakespeare, working in the 16th and 17th centuries, made a character called Satan, the “prince of darkness” (King Lear: III, iv) and gave darkness jaws with which to devour love. (A Midsummer Night’s Dream: I, i)[5] Chaucer, a 14th century Middle English writer, wrote that knights must cast away the “workes of darkness.”[6] Dante described hell as “solid darkness stain’d.”[7]
In Old English there were three words that could mean darkness: heolstor, genip, and sceadu.[8] Heolstor also meant “hiding-place” and became holster. Genip meant “mist” and fell out of use like many strong verbs. It is however still used in the Dutch saying "in het geniep" which means secretly. Sceadu meant “shadow” and remained in use. The word dark eventually evolved from the word deorc.[9]