Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared (below red), and cannot be seen by the naked human eye. Red is used as one of the additive primary colors of light, complementary to cyan, in RGB color systems. Red is also one of the subtractive primary colors of RYB color space but not CMYK color space.
Etymology and definitions
The word red comes from the Old English rēad. Further back, the word can be traced to the Proto-Germanic rauthaz and the Proto-Indo European root reudh-. In ...view middle of the document...
 This further drove other adaptations to take advantage of this new ability, such as red faces. Red light is also used to preserve night vision in low-light or night-time situations, as the rod cells in the human eye aren't sensitive to red. Red is one of the three additive primary colors of light, complementary to cyan, in RGB color systems. Red is also one of the three subtractive primary colors of RYB color space but not CMYK color space.
One common use of red as an additive primary color is in the RGB color model. Because red is not by itself standardized, color mixtures based on red are not exact specifications of color either. The United States government sets certain specifications for what paints to use when red is stated in a design. In order for computers to produce exact colors, the color red needs to be defined in terms of an absolute color space, such as sRGB. color correction (so that a standardized red is produced that is not in fact full intensity of only the red colorant).
Red illumination was (and sometimes still is) used as a safelight while working in a darkroom, as it does not expose most photographic paper and some films. Though many more modern darkrooms use an amber safelight, red illumination is closely associated with the darkroom in the public mind.
Mars possesses a distinct red color, particularly when seen up close
Mars is called the Red Planet because of the reddish color imparted to its surface by the abundant iron oxide present there. Astronomical objects which are moving away from the observer exhibit a red shift. Jupiter's surface displays a Great Red Spot, a football-shaped gigantic storm south of the planet's equator. Many elements exhibit a red color when burned; calcium, for example, produces a brick-red when combusted..
Red blood cells on agar plates
Oxygenated blood is red due to the presence of oxygenated hemoglobin. When used about animal coloration red usually refers to a brownish, reddish-brown or ginger color. In this sense it is used to describe coat colors of reddish-brown cattle and dogs, and in the names of various animal species or breeds such as red fox, red squirrel, red deer, Robin Redbreast, Red Grouse, Red Knot, Redstart, Redwing, Red Setter, Red Devon cattle etc. The usage for animal color appears similar to that for red ochre, red hair and Red Indian. When used for flowers, red often refers to purplish (red deadnettle, red clover, red helleborine) or pink (red campion, red valerian) colors.
Red is associated dominance in a number of animal species. For example, in mandrills red coloration of the face is greatest in alpha males, increasingly less prominent in lower ranking subordinates, and directly correlated with levels of testosterone. Red can also affect the perception of dominance by others, leading to significant differences in mortality, reproductive success and parental investment between...