question: Why do colours look different in artificial light to the way they appear in sunlight?
comment: Artificial light doesn't produce the same spectrum of colors (which combine to form "white" light) as natural sunlight does. Imagine if the frequency of light that we perceive as red was missing from sunlight - nothing outdoors would appear red to us, as no red light from the spectrum would be reflecting off those objects for us to see. The same thing happens indoors - artificial lights may have a little more yellow or less blue or whatever in their spectrum; not enough for us to notice right away, but enough to make objects appear to be a slightly different color.
passages: 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.
   Spectral rendering can also simulate light sources and objects more effectively, as the light's emission spectrum can be used to release photons at a particular wavelength in proportion to the spectrum. Objects' spectral reflectance curves can similarly be used to reflect certain portions of the spectrum more accurately.
  
  As an example, certain properties of tomatoes make them appear differently under sunlight than under fluorescent light. Using the blackbody radiation equations to simulate sunlight or the emission spectrum of a fluorescent bulb in combination with the tomato's spectral reflectance curve, more accurate images of each scenario can be produced.
  
  Section::::Implementations.
   Most digital cameras have means to select color correction based on the type of scene lighting, using either manual lighting selection, automatic white balance, or custom white balance. The algorithms for these processes perform generalized chromatic adaptation.
   There is a large literature on how one might estimate the ambient lighting from the camera data and then use this information to transform the image data. A variety of algorithms have been proposed, and the quality of these has been debated. A few examples and examination of the references therein will lead the reader to many others. Examples are Retinex, an artificial neural network or a Bayesian method.
  
  Section::::Chromatic colors.
   Section::::Bioinspired periodic/aperiodic structures.
  
  Structural color is a type of coloration that arises from the interaction of light with nano-sized structures. This interaction is possible because these photonic structures are of the same size as the wavelength of light. Through a mechanism of constructive and destructive interference, certain colors get amplified, while others diminish.
   BULLET::::- Color rendition: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can make the color of objects appear differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism, red surfaces being rendered particularly poorly by typical phosphor-based cool-white LEDs. The same is true with green surfaces.
   In colour photography, different coloured lights can be used to affect pseudo-solarization, but the results become even less predictable.
  
  Using the Sabattier effect it should be obvious that it is very difficult to manage all parameters for yielding consistent and predictable results and therefore other means have been pursued such as Agfacontour and special pseudo-solarizing developers
   In contrast, when using multivariate optical computing, the light entering the instrument strikes an application specific multivariate optical element, which is uniquely tuned to the pattern that needs to be measured using multivariate analysis.
   The above-mentioned chromatic aberrations, due to mask-induced apodization, also lead to inconsistent source-mask optimizations for different wavelengths.
  
  Section::::Enhancement opportunities for EUV patterning.:Optimum illumination vs. pitch.
   Also the printing industry is affected by metamerism. Inkjet printers do the mixing of colors under a specific light source, resulting in a modified appearance of original and copy under different light sources. One way to minimize metamerism in printing is by first measuring the spectral reflectance of an object or reproduction using a color measurement device. Then, one selects a set of ink compositions corresponding to the color reflectance factor, which are used by the inkjet printer for the reproduction. The process is repeated until original and reproduction present an acceptable degree of metamerism. Sometimes, however, one reaches the conclusion that an improved match is not possible with the materials available either due to gamut limitations or colorimetric properties.
   Section::::Components and action.:Photon.
  
  Photoexcitation of the pigment molecules in the antenna complex induces electron transfer.
  
  Section::::Components and action.:Antenna complex.
   Cryptochromes are another type of photoreceptor that is important in photoperiodism. Cryptochromes absorb blue light and UV-A. Cryptochromes entrain the circadian clock to light. It has been found that both cryptochrome and phytochrome abundance relies on light and the amount of cryptochrome can change depending on day-length. This shows how important both of the photoreceptors are in regards to determining day-length.
   Sources that rely on fluorescence have a different emission spectrum shape than do thermal sources. Some wavelengths will be produced with greater amplitude than others. Fluorescent sources used for lighting, such as fluorescent lamps, white light emitting diodes, and metal halide lamps are intended to produce light at all wavelengths, but the distribution is different from thermal sources and so colors will appear different under these forms of lighting than under daylight; some colors may match under one light source that don't appear the same under another, a phenomenon called metamerism.
   Figure 7: Comparison between PAM and 2PAM images of melanin distribution.
  
  Section::::Super resolution techniques.:Structured illumination.
   As a result of these favorable "differential kinetics", DSSCs work even in low-light conditions. DSSCs are therefore able to work under cloudy skies and non-direct sunlight, whereas traditional designs would suffer a "cutout" at some lower limit of illumination, when charge carrier mobility is low and recombination becomes a major issue. The cutoff is so low they are even being proposed for indoor use, collecting energy for small devices from the lights in the house.
   To solve problems such as these, the HSL and HSV models scale the chroma so that it always fits into the range for every combination of hue and lightness or value, calling the new attribute "saturation" in both cases (fig. 14). To calculate either, simply divide the chroma by the maximum chroma for that value or lightness.
   The Nayatani et al. color appearance model focuses on illumination engineering and the color rendering properties of light sources.
  
  Section::::Color appearance models.:Hunt model.
   Problems have been encountered attempting to use LED lighting on film and video sets. The color spectra of LED lighting primary colors does not match the expected color wavelength bandpasses of film emulsions and digital sensors. As a result, color rendition can be completely unpredictable in optical prints, transfers to digital media from film (DI's), and video camera recordings. This phenomenon with respect to motion picture film has been documented in an LED lighting evaluation series of tests produced by the Academy of Motion Picture Arts and Sciences scientific staff.
   The first architectural integration was demonstrated at EPFL's new convention center in partnership with Romande Energie. The total surface is 300 m, in 1400 modules of 50 cm x 35 cm. Designed by artists Daniel Schlaepfer and Catherine Bolle.
  
  Section::::Development.:New developments.:2018.
   Research is in progress at universities such as Radboud University Nijmegen and Delft University of Technology. For example, at Massachusetts Institute of Technology researchers have developed approaches for conversion of windows into sunlight concentrators for generation of electricity. They paint a mixture of dyes onto a pane of glass or plastic. The dyes absorb sunlight and re-emit it as fluorescence within the glass, where it is confined by internal reflection, emerging at the edges of the glass, where it encounters solar cells optimized for conversion of such concentrated sunlight. The concentration factor is about 40, and the optical design yields a solar concentrator that unlike lens-based concentrators, need not be directed accurately at the sun, and can produce output even from diffuse light. Covalent Solar is working on commercialization of the process.
   This section describes some of the color appearance phenomena that color appearance models try to deal with.
  
  Section::::Color appearance phenomena.:Chromatic adaptation.
   Section::::Dye-sensitized solar cells.:Disadvantages.
   Section::::Dye-sensitized solar cells.:Mechanism of DSSCs.
  
  The following steps convert in a DSSC photons (light) to current:
  
  The efficiency of a DSSC depends on four energy levels of the component: the excited state (approximately LUMO) and the ground state (HOMO) of the photosensitizer, the Fermi level of the TiO electrode and the redox potential of the mediator (I/I) in the electrolyte.
  
  Section::::Dye-sensitized solar cells.:Nanoplant-like morphology.
   Each of the three types of cones in the retina of the eye contains a different type of photosensitive pigment, which is composed of a transmembrane protein called opsin and a light-sensitive molecule called 11-cis retinal. Each different pigment is especially sensitive to a certain wavelength of light (that is, the pigment is most likely to produce a cellular response when it is hit by a photon with the specific wavelength to which that pigment is most sensitive). The three types of cones are L, M, and S, which have pigments that respond best to light of long (especially 560 nm), medium (530 nm), and short (420 nm) wavelengths respectively.
   Two different light spectra that have the same effect on the three color receptors in the [[human eye]] will be perceived as the same color. They are [[Metamerism (color)|metamers]] of that color. This is exemplified by the white light emitted by fluorescent lamps, which typically has a spectrum of a few narrow bands, while daylight has a continuous spectrum. The human eye cannot tell the difference between such light spectra just by looking into the light source, although reflected colors from objects can look different. (This is often exploited; for example, to make [[fruit]] or [[tomato]]es look more intensely red.)
  
raw_presuppositions: Colors should look the same in all light.
raw_corrections: Artificial light doesn't have the same colors in it to reflect out. 