Answer:
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. 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.
Scientific
Perception
The perception of darkness differs from the mere absence of light due to the effects of after images on perception. In perceiving, the eye is active, and the part of the retina that is unstimulated produces a complementary afterimage.
Physics
In terms of physics, an object is said to be dark when it absorbs photons, causing it to appear dim compared to other objects. For example, matte black paint does not reflect much visible light and appears dark, whereas white paint reflects lots of light and appears bright. For more information, see color. An object may appear dark, but it may be bright at a frequency that humans cannot perceive.
A dark area has limited light sources, making things hard to see. Exposure to alternating light and darkness has caused several evolutionary adaptations to darkness. When a vertebrate, like a human, enters a dark area, its pupils dilate, allowing more light to enter the eye and improving night vision. Also, the light detecting cells in the human eye 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.
The material known as Vantablack is one of the darkest substances known, absorbing up to 99.965% of visible light is a material developed by Surrey NanoSystems in the United Kingdom. The name is a compound of the acronym VANTA and the color black.
Technical
The color of a point, on a standard 24-bit computer display, is defined by three RGB values, each ranging from 0-255. When the red, green, and blue components of a pixel are fully illuminated, the pixel appears white; when all three components are unilluminated, the pixel appears black.
Cultural
Artistic
Artists use darkness to emphasize and contrast the presence of light. Darkness can be used as a counterpoint to areas of lightness to create leading lines and voids. Such shapes draw the eye around areas of the painting. Shadows add depth and perspective to a painting. See chiaroscuro for a discussion of the uses of such contrasts in visual media.
Color paints are mixed together to create darkness, because each color absorbs certain frequencies of light. Theoretically, mixing together the three primary colors, or the three secondary colors, will absorb all visible light and create black. In practice it is difficult to prevent the mixture from taking on a brown tint.
Literature
As a poetic term in the Western world, darkness is used to connote the presence of shadows, evil, and foreboding, or in modern parlance, to connote that a story is grim, heavy, and/or depressing.
Religion
The first creation narrative in Christianity begins with darkness, into which is introduced the creation of light, and the separation of this light from the darkness . Thus, although both light and darkness are included in the comprehensive works of the almighty God—darkness was considered "the second to last plague", and the location of "weeping and gnashing of teeth" .
Erebus was a primordial deity in Greek mythology, representing the personification of darkness.
Philosophy
In Chinese philosophy, Yin is the complementary feminine part of the Taijitu and is represented by a dark lobe.
Poetry
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