Glossary

• Achromatic color
  Color devoid of hue (white, black, grey, neutral).
  
• Candela, cd
  The unit of luminous intensity. The candela is the liminous intensity, in a given direction, of a source emitting a monochromatic radiation of frequency 540 x 10¹² Hz, the radiant intensity of which in that direction is equal to 1/683 Watt per steradian.
  
• Chromatic color
  Color exhibiting hue, as opposed to achromatic color.
  
• Chromaticity coordinates
  Ratio of each of a set of tristimulus values to their sum.
  
• Chromaticity diagram
  A two-dimentional diagram in which points specified by chromaticity coordinates represent the chromaticities of color stimuli.
  
• CIE (Commission Internationale de l'Êclairage)
  The International Commission on Lighting; the body responsible for international recommendations for photometry and colorimetry.
  
• CIE 1931 standard colorimetric observer
  An ideal observer whose color matching properties correspond to the CIE color matching functions for the 2º field size.
  
• CIE 1964 supplementary standard colorimetric observer
  An ideal observer whose color matching properties correspond to the CIE color matching functions for the 10º field size.
  
• CIELAB (CIE L*a*b*) color space
  The color space in which L*, a* and b* are plotted at right angles to one another. Equal distances in the space represent approximately equal color difference.
  
• CIE primaries
  The three standard primaries, defined by CIE in 1931 and called X, Y, Z, that can be used to match, with only positive weights, all visible colors. The Y primary is intentionally defined to have a color-matching function that exactly matches the luminous-efficiency function of the human eye.
  
• CIE XYZ color space
  The cone-shaped space formed by (x, y, z) weights, that when applied to the CIE primaries, match any visible color.
  
• Color matching functions
  The tristimulus values of monochromatic stimuli of equal radiant power.
  
• Color temperature
  The temperature of the Planckian radiator whose radiation has the same chromaticity as that of a given stimulus.
  
• Complementary colors
  Colors that can be additively mixed to produce as achromatic color.
  
• Complementary wavelength
  The wavelength of the monochromatic stimulus that, when additively mixed with the color stimulus considered, matches the specified achromatic stimulus.
  
• Cones
  Photoreceptors in the retina that contain light-sensitive pigments capable of initiating the process of photopic vision.
  
• D illuminants
  CIE Standard Illuminants that have a relative spectral power distribution representing the phases of daylight with different correlated color temperature.
  
• Dominant wavelength
  The wavelength of the color corresponding to the perceptual notion of hue. On the chromaticity diagram, the dominant wavelength is defined as the wavelength of the point on the spectral locus, corresponding to the intersection of the locus with a line drawn from the reference white through the color in question.
  
• Gamut (color gamut)
  The entire range of perceived color that may be obtained under specified conditions.

• Lumen, lm
  The unit of luminous flux. The lumen is the luminous flux emitted within 1 steradian by a point source having a luminous intensity of 1 candela.
  
• Purple boundary
  The line in a chromaticity diagram that represents additive mixtures of monochromatic stimuli of wavelengths approximately 380 and 780 nm.
  
• Saturation
  The colorfulness of an area judged in proportion to its brightness.
  
• Spectrophotometry
  Measurements of the relative amounts of radiant flux at each wavelength of the spectrum.
  
• Transformation equations
  A set of three simultaneous equations used to transform a color specification from one set of matching stimuli to another.
  
• Tristimulus values
  Amounts of the three matching stimuli, in a given trichromatic system, required to match the stimulus being considered.
  
• x,y diagram
  Chromaticity diagram in with the (x,y) chromaticity coordinates of the CIE XYZ system are used.