The emotional response to darkness has generated metaphorical usages of the term in many cultures.
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 that part of the retina that is unstimulated produces a complementary afterimage.
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, a matte black paint does not reflect much visible light and appears dark, whereas white paint reflects much light and appears bright. For more information see color.
Light cannot be absorbed without limit. According to the principle of the conservation of Energy, energy cannot be created or destroyed; it can only be converted from one type to another. Consequently, most objects that absorb visible light reemit it as heat. So, although an object may appear dark, it is likely bright at a frequency that humans cannot perceive. 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 pupils dilate, 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)
The color of a point, on a standard 24-bit computer display, is defined by three RGB (red, green, blue) values, each ranging from 0-255. When the red, green, and blue components of a pixel are fully illuminated (255,255,255), the pixel appears white; when all three components are unilluminated (0,0,0), the pixel appears black.
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Artists use darkness to emphasize and contrast with light. Darkness can be used as a counterpoint to areas of lightness to create leading lines and voids[disambiguation needed]. 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.
As a poetic term in the Western world, darkness is used to connote the presence of shadows, evil, and foreboding.
The first day of the biblical creation narrative begins with darkness, into which is introduced the creation of light, and the separation of this light from the darkness (as distinct from the creation of the sun and moon on the fourth day of creation). Thus, although both light and darkness are included in the comprehensive works of the almighty God — darkness was considered "the second to last plague" (Exodus 10:21), and the location of "weeping and gnashing of teeth.” (Matthew 8:12)
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 the “prince of darkness” (King Lear: III, iv) and gave darkness jaws with which to devour love. (A Midsummer Night’s Dream: I, i) Chaucer, a 14th-century Middle English writer, wrote that knights must cast away the “workes of darkness.” Dante described hell as “solid darkness stain’d.”
In Old English there were three words that could mean darkness: heolstor, genip, and sceadu. 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.
- David T. Horner, Demonstrations of Color Perception and the Importance of Contours, Handbook for Teaching Introductory Psychology, Volume 2, page 217. Psychology Press, Texas, 2000) "Afterimages are the complementary hue of the adapting stimulus and trichromatic theory fails to account for this fact". http://books.google.ca/books?id=qyjYzloWfoMC&lpg=PA217&ots=fdXFRLg7GZ&dq=retina%20that%20is%20unstimulated%20produces%20a%20complementary%20afterimage&pg=PA216#v=onepage&q=retina%20that%20is%20unstimulated%20produces%20a%20complementary%20afterimage&f=false
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- Dr. Denise Smith. Exploring the Electromagnetic Spectrum: The Herschel Experiment (powerpoint). Space Telescope Science Institute. Archived from the original on 2007-02-06. Retrieved 2007-01-21.
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- Shakespeare, William. "The Complete Works". The Tech, MIT.
- Chaucer, Geoffrey (14th century). The Canterbury Tales, and Other Poems. The Second Nun’s Tale.
- Alighieri, Dante; Translated by: Henry Francis (14th century). The Divine Comedy.
- Mitchell, Bruce; Fred C. Robinson (2001). A Guide to Old English. Glossary: Blackwell Publishing. pp. 332, 349, 363, 369. ISBN 0-631-22636-2.
- Harper, Douglass (November 2001). "Dark". Online Etymology Dictionary. Retrieved 2007-01-18.