question: why do red pigments fade quicker than others in sunlight?
comment: Red absorbs more visible light than all the other colors, heating it more and denaturing the pigments
passages: Chlorophylls degrade into colorless tetrapyrroles known as "nonfluorescent chlorophyll catabolites" (NCCs).
  
  As the predominant chlorophylls degrade, the hidden pigments of yellow xanthophylls and orange beta-carotene are revealed. These pigments are present throughout the year, but the red pigments, the anthocyanins, are synthesized "de novo" once roughly half of chlorophyll has been degraded. The amino acids released from degradation of light harvesting complexes are stored all winter in the tree's roots, branches, stems, and trunk until next spring when they are recycled to re‑leaf the tree.
  
  Section::::Pigments in animals.
   Exposure to ultraviolet radiation, solvents and high temperatures reduce the lifespan of leuco dyes. Temperatures above about typically cause irreversible damage to leuco dyes; a time-limited exposure of some types to about is allowed during manufacturing.
   Red lake pigments were an important part of the palette of 16th-century Venetian painters, particularly Titian, but they were used in all periods. Since the red lakes were made from organic dyes, they tended to be fugitive, becoming unstable and fading when exposed to sunlight.
  
  Section::::In science and nature.:Food coloring.
  
  The most common synthetic food coloring today is Allura Red AC is a red azo dye that goes by several names including: Allura Red, Food Red 17, C.I. 16035, FD&C Red 40, It was originally manufactured from coal tar, but now is mostly made from petroleum.
   Anthocyanins are present in about 10% of tree species in temperate regions, although in certain areas—a famous example being New England—up to 70% of tree species may produce the pigment. In autumn forests they appear vivid in the maples, oaks, sourwood, sweetgums, dogwoods, tupelos, cherry trees and persimmons. These same pigments often combine with the carotenoids' colors to create the deeper orange, fiery reds, and bronzes typical of many hardwood species. (See Autumn leaf color).
  
  Section::::In science and nature.:Blood and other reds in nature.
   Color indices of distant objects are usually affected by interstellar extinction, that is, they are redder than those of closer stars. The amount of reddening is characterized by color excess, defined as the difference between the observed color index and the normal color index (or intrinsic color index), the hypothetical true color index of the star, unaffected by extinction.
  
  For example, in the UBV photometric system we can write it for the B−V color:
   The somatic, or X-linked inheritance patterns of RP are currently identified with the mutations of six genes, the most common occurring at specific loci in the RPGR and RP2 genes.
  
  Types include:
  
  Section::::Pathophysiology.
   During the summer growing season, phosphate is at a high level. It has a vital role in the breakdown of the sugars manufactured by chlorophyll. But in the fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant. When this happens, the sugar-breakdown process changes, leading to the production of anthocyanin pigments. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting color display. When the days of autumn are bright and cool, and the nights are chilly but not freezing, the brightest colorations usually develop.
   The appearance of pigments is intimately connected to the color of the source light. Sunlight has a high color temperature and a fairly uniform spectrum and is considered a standard for white light, while artificial light sources tend to have strong peaks in parts of their spectra. Viewed under different lights, pigments will appear different colors.
  
  Color spaces used to represent colors numerically must specify their light source. Lab color measurements, unless otherwise noted, assume that the measurement was taken under a D65 light source, or "Daylight 6500 K", which is roughly the color temperature of sunlight.
   Section::::In graphical industry.
  
  In printing inks mainly organic pigments are used, so shifting or bleaching of the color of a printing product due to presence of the UV light is usually just a matter of time. The usage of the organic pigments is justified especially by their inexpensive price comparing to inorganic pigments. The particle size of the inorganic pigments is often larger than on organic pigments thus all inorganic pigments are not suitable to be used in the offset printing.
   Early "non colour-sensitive" (NCS) films, plates and papers were only sensitive to the high-energy end of the visible spectrum from green to UV (shorter-wavelength light). This would render a print of the red areas as a very dark tone because the red light was not actinic. Typically, light from xenon flash lamps is highly actinic, as is daylight as both contain significant green-to-UV light.
   Paints, inks and dyes that are organic are more susceptible to photodegradation than those that are not. Ceramics are almost universally colored with non-organic origin materials so as to allow the material to resist photodegradation even under the most relentless conditions, maintaining its color.
  
  Section::::Applications.:Pesticides and herbicides.
   Photosensitivity reactions are characterized by severe inflammation of the skin with depigmentation and ulceration. In some cases (Type I), pigments are excreted through urine or deposited in hard tissues such as bones and teeth, causing discolouration. Affected animals should be protected from direct sunlight until the photodynamic compounds have been completely eliminated from the body or the appropriate treatments have been given.
  
  Section::::Biological mechanism of photosensitivity reactions.
   Section::::Role in the circadian pathways.:Circadian output.
   These types of phosphorescent pigments, often called lume, operate like a light battery. After sufficient activation by sunlight or artificial light, they glow in the dark for hours. Larger markings are visible for the whole night. This activation and subsequent light emission process can be repeated again and again, and the material does not suffer any practical aging. Strontium aluminate–based pigments have to be protected against contact with water or moisture, since this degrades the light emitting quality.
  
  Section::::Alternative for afterglow pigments.
   Photo-oxidation, "i.e.," photochemical oxidation. A colorant molecule, when excited by a photon of sufficient energy, undergoes an oxidation process. In the process the chromophoric system of the colorant molecule reacts with the atmospheric oxygen to form a non-chromophoric system, resulting in fading. Colorants which contain a carbonyl group as the chromophore are particularly vulnerable to oxidation.
  
  Section::::Chemical processes.:Photoreduction.
   Chlorophylls degrade into colorless tetrapyrroles known as nonfluorescent chlorophyll catabolites.
  
  As the chlorophylls degrade, the hidden pigments of yellow xanthophylls and orange beta-carotene are revealed. These pigments are present throughout the year, but the red pigments, the anthocyanins, are synthesized "de novo" once roughly half of chlorophyll has been degraded. The amino acids released from degradation of light harvesting complexes are stored all winter in the tree's roots, branches, stems, and trunk until the next spring, when they are recycled to releaf the tree.
  
  Section::::Pigments that contribute to other colors.
  
  Section::::Pigments that contribute to other colors.:Carotenoids.
   Section::::Standards and measure scales.
  
  Some organizations publish standards for rating the lightfastness of pigments and materials. Testing is typically done by controlled exposure to sunlight, or to artificial light generated by a xenon arc lamp. Watercolors, inks, pastels, and colored pencils are particularly susceptible to fading over time, so choosing lightfast pigments is especially important in these media.
   Type II Photosensitivity is caused by inborn errors in the metabolism of certain biological pigments. In the absence of some key metabolic enzymes, the products of intermediary metabolism accumulate. They are either eliminated through the urine and body fluids or are deposited in some body tissue, such as bone and teeth. A common condition seen in animals is congenital porphyria due to the accumulation of Uroporphyrin, which is deposited in the teeth and bones, giving them a pink discolouration, or excreted through the urine, exhibiting a pinkish fluorescence under ultraviolet light.
  
  Section::::Classification of photosensitivity reactions.:Type III Photosensitivity.
   BULLET::::- Betalains are red or yellow pigments. Like anthocyanins they are water-soluble, but unlike anthocyanins they are synthesized from tyrosine. This class of pigments is found only in the Caryophyllales (including cactus and amaranth), and never co-occur in plants with anthocyanins. Betalains are responsible for the deep red color of beets.
  
  A particularly noticeable manifestation of pigmentation in plants is seen with autumn leaf color, a phenomenon that affects the normally green leaves of many deciduous trees and shrubs whereby they take on, during a few weeks in the autumn season, various shades of red, yellow, purple, and brown.
   Chlorophyll, the most abundant plant pigment, is most efficient in capturing red and blue light. Accessory pigments such as carotenes and xanthophylls harvest some green light and pass it on to the photosynthetic process, but enough of the green wavelengths are reflected to give leaves their characteristic color. An exception to the predominance of chlorophyll is autumn, when chlorophyll is degraded (because it contains N and Mg) but the accessory pigments are not (because they only contain C, H and O) and remain in the leaf producing red, yellow and orange leaves.
   Diketopyrrolopyrrole pigments are an important class of high-performance pigments used in inks, paints and plastic. More recently their optical-electronic performance was discovered for photovoltaic applications and related uses.
  
  Section::::Optical properties.
   Section::::Pigments in animals.:Pigments in marine animals.:Photo-protective pigments.
  
  Due to damage from UV-A and UV-B, marine animals have evolved to have compounds that absorb UV light and act as sunscreen. Mycosporine-like amino acids (MAAs) can absorb UV rays at 310-360 nm. Melanin is another well-known UV-protector. Carotenoids and photopigments both indirectly act as photo-protective pigments, as they quench oxygen free-radicals. They also supplement photosynthetic pigments that absorb light energy in the blue region.
  
  Section::::Pigments in animals.:Pigments in marine animals.:Defensive role of pigments.
   Tetrapyrroles are the next most common group of pigments. They have four pyrrole rings, each ring consisting of CHNH. The main role of the tetrapyrroles is their connection in the biological oxidation process. Tetrapyrroles have a major role in electron transport and act as a replacement for many enzymes. They also have a role in the pigmentation of the marine organism's tissues.
  
  Section::::Pigments in animals.:Pigments in marine animals.:Melanin.
   Section::::In pigments.
  
  In a conjugated pi-system, electrons are able to capture certain photons as the electrons resonate along a certain distance of p-orbitals - similar to how a radio antenna detects photons along its length. Typically, the more conjugated (longer) the pi-system is, the longer the wavelength of photon can be captured. In other words, with every added adjacent double bond we see in a molecule diagram, we can predict the system will be less likely to absorb yellow light (appear more red to our eyes) and more likely to absorb red light (appear more yellow to our eyes).
   When mixing the printing inks the lightfastness of the ink being weaker by its lightfastness defines the lightfastness of the whole color. The fading of one of the pigments leads to tone shift towards to component with better lightfastness. If it is required that there will be something visible from the printing even though its dominant pigment would fade, small amount of pigment with excellent lightfastness can be mixed with it.
  
  Section::::See also.
  
  BULLET::::- Blue Wool Scale – a measure of dye permanence
  
  BULLET::::- Color fastness – resistance to fading of textile colors
  