Glossary of Color Terms


Introduction: The following glossary was borrowed from many sources including the "ASTM" Standards of Color & Appearance. We have also "borrowed" from our own resouces & have assembled an informative color term reference for your convenience.  Any errors are the authors’. We welcome your comments. We do not pretend to provide every term used in our field. Rather, we wanted to include most of the commonly used terms you are likely to see in the literature as it relates to every day use of color computers.


"a", n - Redness-greenness coordinate in certain transformed color spaces (Hunter L,a,b or CIELAB), generally used as the difference in "a" between a specimen and a standard reference color. If "a"  is positive, there is more redness than greenness; if "a" is negative,there is more greenness than redness. It is normally used with b as part of the chromaticity or chromaticity color difference.

absolute data, n  - color measurement data presented without comparison of the sample to a standard or calculated color difference.

absorption, n - (1) penetration of one substance into the mass of another. (2) decrease in directional transmittance of incident radiation (such as light), resulting in a modification or conversion of the absorbed energy, into heat, for example. Light incident on a specimen may be partially reflected, partially transmitted, or partially absorbed.

absorption tinting strength, n – relative change in the absorption properties of a standard white material when a specified amount of an absorbing colorant, black or chromatic is added to it.

accuracy, n – the closeness of agreement between a test result and an accepted reference value (often used as a color instrument specification).

achromatic, adj – (1) for primary light sources, the computed chromaticity of the equal-energy spectrum.        (2) for surface colors, the color of a whitish light, serving as the illuminant, to which adaptation has taken place in the visual system of the observer. (3) perceived as having no hue, that is, as white, gray, or black.

additive color mixture, n – superposition or other nondestructive combination of lights of different perceived colors.

angle of illumination, n – angle between the specimen normal and the illuminator axis.

angle of view, n – angle between the normal to the surface of the specimen and the axis of the receiver.

aperture, n - the measurement opening in a typical reflection color instrument. The size of the aperture determines the size and type of sample that can be measured.

appearance, n -- manifestation of the nature of objects and materials through visual attributes such as size, shape, color, texture, glossiness, transparency, opacity, etc.

artificial daylight, n -- term loosely applied to light sources, frequently equipped with filters, which are claimed to reproduce the color and spectral distribution of daylight. A more specific definition of the light source is to be preferred.

attributes of color, n – (1) for the object mode of appearance, hue, lightness, and saturation. In the Munsell system, Munsell Hue, Munsell Value, and Munsell Chroma. (2) for the illuminant or aperture mode, hue, brightness, and saturation.

averaging, vt – a method of color measurement that allows you to average several measurements into one color measurement. Averaging is recommended when measuring standards or samples with surface variation. Usually the sample is turned 90° between measurements.

"b", n -- yellowness-blueness coordinate in certain color spaces (Hunter L,a,b & CIELAB), generally used as the difference in "b" between a specimen and a standard reference color, normally used with "a" or "a" as part of the chromaticity difference. Generally, if "b" is positive, there is more yellowness than blueness; if "b" is negative, there is more blueness than yellowness.

basic color terms, n – a group of 11 color names found in anthropological surveys to be in wide use in fully developed languages: white, black, red, green, yellow, blue, brown, gray, orange, purple, pink.

Beer’s law, n – the absorbence of a homogeneous sample containing an absorbing substance is directly proportional to the concentration of the absorbing substance, often used in mixture prediction of transparent materials.

black, n -- ideally, the complete absorption of incident light; the absence of any reflection. In the practical sense, any color that is close to this ideal in a relative viewing situation, i.e., a color of very low saturation and of low luminance.

brightness, n – (1) aspect of visual perception whereby an area appears to emit more or less light;  (2) of an object color, combination of lightness and saturation; (3) in the textile industry, perceived as saturated, vivid, deep, or clean. (color);  (4) of paper, reflectance of an infinitely thick specimen (reflectivity) measured for blue light with a centroid wavelength of 457 nm under specified spectral and geometric conditions of measurement. (5) dyer’s, the color quality, combining lightness and saturation that would be decreased by adding black, gray, or a complementary color to a chromatic dye.

bronzy color (or bronzing), n – a metallic coloration observed when viewing the light reflected at angles near the angle of specular reflection, the color usually being quite different from that observed for other directions (i.e., paint samples).

C or Delta c, n -- abbreviations for chromaticity or chromaticity difference, respectively.

calibrate, vtto find and eliminate systematic errors of an instrument scale or method of instrument by use of material standards and techniques traceable to an authorized national or international measurement system.

characterize, vt – to specify the parameters or performance of an instrument, method of measurement, or material absorption and scatter.

chroma, n – (1) attribute of color used to indicate the degree of departure of the color from a gray of the same lightness. (2) C*, (in the CIE 1976 L*, a*, b* or L*, u*, v* system) the quantity C*ab = (a*2 + b*2)1/2 or C*uv = (u*2 + v*2)1/2.  (3) attribute of a visual perception, produced by an object color that permits a judgment to be made of the amount of pure chromatic color present, irrespective of the amount of achromatic color.

chromatic, adj – perceived as having a hue; not white, gray, or black. (opposite of achromatic)

chromaticity, n -- dimensions of a color stimulus expressed in terms of hue and saturation, or redness-greenness and yellowness-blueness, excluding the luminous intensity; generally expressed as a point in a plane of constant luminance. Syn: chromaticness.

chromaticity coordinates, CIE, n -- the ratios of each of the three tristimulus values X, Y and Z in relation to the sum of the three; designated as x, y and z, respectively. They are sometimes referred to as the trichromatic coefficients. When written without subscripts, they are assumed to have been calculated for Illuminant C and the 2° (1931) Standard Observer unless specified otherwise. If they have been obtained for other illuminants or observers, a subscript describing the observer or illuminant should be used. For example, x10 and y10 are chromaticity coordinates for the 10° observer and Illuminant C.

chromaticity diagram, CIE, n -- a two-dimensional graph of the chromaticity coordinates, x as the abscissa and y as the ordinate, which shows the spectrum locus (chromaticity coordinates of monochromatic light, 380-770 nm). It has many useful properties for comparing colors of both luminous (light emitting) and nonluminous (reflective) materials.

CIE, n – the abbreviation for the French title of the International Commission on Illumination, Commission Internationale de l’Eclairage.

CIE 1931 standard observer, n – ideal colorimetric observer with color matching functions x-(y), y-(y), z-(y) corresponding to a field of view subtending a 2º angle on the retina; commonly called the "2º standard observer."

CIE 1964 supplementary standard observer, n – ideal colorimetric observer with color matching functions x-10(y), y-10(y), z-10(y) corresponding to a field of view subtending a 10º angle on the retina; commonly called the "10º standard observer."

CIELAB color difference, n – color difference calculated by using the CIE 1976 L* a* b* opponent-color scales (also referred to as CIELAB), based on applying a cube-root transformation to CIE 1931 tristimulus values X, Y, Z or CIE 1964 tristimulus values X10, Y10, Z10.

clarity, n – the characteristic of a transparent body whereby distinct high-contrast images or high-contrast objects (separated by some distance from the body) are observable through the body.

cmc (l:c) color difference, n – color difference calculated by use of the formula developed by the Colour Measurement Committee of the Society of Dyers and Colourists of Great Britain.

Discussion Based on the lightness, hue, chroma version of CIELAB, it incorporates chroma and hue-angle correction terms for improved visual spacing and variable weighting factors for lightness (l) and chroma (c) relative to hue for improved correlation depending on type of judgment (acceptability, perceptibility) and application (textiles, others). CMC reports the equivalent of D E as a weighted function of the ratio of L:Ch as Performance Factor=PF.

color, n – (1) of an object, aspect of object appearance distinct from form, shape, size, position, or gloss that depends upon the spectral composition of the incident light, the spectral reflectance of transmittance of the object, and the spectral response of the observer, as well as the illuminating and viewing geometry.  (2) perceived, attribute of visual perception that can be described by color names such as white, gray, black, yellow, brown, vivid red, deep reddish purple, or by combinations of such names.  (3) psychophysical, characteristics of a color stimulus (that is, light producing a sensation of color) denoted by a colorimetric specification with three values, such as tristimulus values.

colorant, n – dye, pigment, or other agent used to impart a color to a material.

color atlas, n – a collection of color samples arranged according to a color order system (such as Munsell, NCS, DIN).

color constancy, n – the general tendency of the colors of an object to remain constant when the color of the illumination is changed.

color difference, n – (1) perceived, the magnitude and character of the difference between two colors described by such terms as redder, bluer, lighter, darker, grayer, or cleaner.  (2) computed, the magnitude and direction of the difference between two psychophysical color stimuli and their components computed from tristimulus values, or chromaticity coordinates and luminance factor, by means of a specified set of color-difference equations.

color-difference units, n – units of size of the color differences calculated according to various equations. Such color differences cannot be accurately converted between different equations by the use of average factors.

colorimeter tristimulus, n – instrument that measures psychophysical color, in terms of tristimulus values, by the use of filters to convert the relative spectral power distribution of the illuminator to that of a standard illuminant, and to convert the relative spectral responsively of the receiver to the responsivities prescribed for a standard observer. See spectrocolorimeter.

colorimetry, n – the science of color measurement.

colorist, n -- a person skilled in the art of color matching (colorant formulation) and knowledgeable concerning the behavior of colorants in a particular material; a tinter (q.v.) (in the American usage) or a shader.

color match, n – (1) condition existing when colors match within a specified or agreed tolerance. Sometimes called commercial color match. (2) condition existing when colors are indistinguishable; a normal observer is usually implied. Sometimes called an exact color match.

color matching, n – procedure for providing, by selection, formulation, adjustment, or other means, a trial color that is indistinguishable from, or within specified tolerances of, a specified standard color under specified conditions.

color-matching functions, n -- the amounts, in any trichromatic system, of the three-reference color stimuli needed to match by an additive mixture monochromatic components of an equal energy spectrum.

color measurement, n -- physical measurement of light radiated, transmitted, or reflected by a specimen under specified conditions and mathematically transformed into standardized colorimetric terms that can be correlated with visual evaluations of color relative to one another. Although the term "color measurement" is normally used, color itself cannot be measured.

color order systems, n – a rational method or plan of ordering and specifying all object colors, or all within a limited domain, by means of a set of material standards selected and displayed so as to represent adequately the whole set of object colors under consideration.

color perception, n – subjective impression of color, as modified by the conditions of observation and by mental interpretation of the stimulus object.

color space, n – a geometric space, usually of three dimensions, in which colors are arranged systematically.

color specification, n – notation or set of three color-scale values used to designate a color in a specified color system. Practical color specifications may include color tolerances as well as target color designation, measuring instrument, instrument settings, measurement procedures and sample preparation procedures.

color stimulus, n – a radiant flux capable of producing a color perception.

color temperature, n – of a light source, the temperature, usually expressed in kelvins, of a full radiator (perfect, theoretical black substance that when heated would not affect the "color" of the light emitted) which emits light of the same chromaticity as the source. For example average daylight color temperature is often expressed as D65, for 6,500 degrees Kevin.

color tolerance, n – the permissible color difference between sample and specified color (Standard).

color tolerance set, n – a group of colored standards, usually seven painted chips, arranged on a single card, one exhibiting a desired color, and two each exhibiting the limits of the permissible range of color variation in each of the color attributes. Normally the set is arranged as the acceptable limits in lightness to darkness, redness to greenness, yellowness to blueness.

contrast, n – objective, the degree of dissimilarity of a measured quantity such as luminance of two areas, expressed as a number computed by a specified formula.

contrast ratio, n – see, contrast or opacity. In color measurement, a sample is measured over a white background, then over a black background and the ratio expressed either as  a perctentage (where 100% = complete opacity) or as a ratio to 1.  (

crazing, n – a network of apparent fine cracks on or beneath the surface of materials, such as in transparent plastics, glazed ceramics, glass, or clear coatings.

daylight illuminants, CIE, n -- series of illuminant spectral power distribution curves based on measurements of natural daylight and recommended by the CIE in 1965. Values are defined for the wavelength region 300 to 830 nm. They are described in terms of the correlated color temperature. The most important is D6500 (often referred to as average daylight) because of the closeness of its correlated color temperature to that of Illuminant C = 6774 K. D7500, bluer than D6500 and D5000, yellower than D6500, are also used.

densitometer, n – instrument designed for measuring optical density of a photographic negative or positive or a printed image; not suitable for colorimetry.

densitometry, n – technique for measurement of optical density by use of a densitometer.

detector, n – device to convert radiant energy (light) into a neural signal (such as the eye) or an electrical signal (such as a phototube, photomultiplier tube, photocell, photodiode, or the like).

diffuse reflection, n – reflection in which flux is scattered in many directions by diffusion at or below the surface.

directionality, n – (1) perceived, the degree to which the appearance of a surface changes as the surface is rotated in its own plane, under fixed conditions of illumination and viewing. In color the addition of metal flake and or pearlescent pigments will greatly increase the visual color effects. Surface striation and texture may also greatly change color appearance. (2) measured –- (scattering indicatrix, azimuthally nonisotropic) – difference in pattern of near-specular and semidiffusely scattered light, dependent upon the azimuthal angles of the incident and viewing beams.

dominant wavelength, n – the wavelength of a spectrally pure light that, when added to a reference achromatic (white) light, will produce a combination that matches the color of a specimen light.

Delta D ,n -indicates deviation or difference.

Delta E, Delta e, D E, D e n -- the total color difference computed with a color difference equation. It is generally calculated as the square root of the sum of the squares of the chromaticity difference, D a + D b, and the lightness difference, D L; in CMC identified as the "commercial factor" (CF).

eggshell, adj – semi-matte, having a texture resembling that of the outer surface of the shell of a chicken egg. Usually used in describing a type of paint finish.

fading, n – a change in color, usually to a lighter and less-saturated color, normally over time caused by the effects of light and other environmental effects on the colorants in a material.

flat, adj (1) of a coating material, a material that is capable of imparting a finish free of gloss. (2) of a surface finish, free of gloss.

flop, n – a difference in color and appearance of a material viewed over two widely different aspecular angles.

flop angle, n – the aspecular angle when a material is viewed from a direction far from the specular, typically 70º or more, normally associated with a change in color and appearance at two viewing angles.

fluorescence, n – a process by which radiant flux of certain wavelengths is absorbed and reradiated nonthermally at other, usually longer, wavelengths. (this phenomenon creates colors that show an abnormal color response and are used for packaging and other dramatic effects).

fluorescent illuminant, n – illuminant representing the spectral distribution of the radiation from a specified type of fluorescent lamp (as expressed as a set of data in color computer programs).

FMC-2 color difference, n – color difference calculated by use of the Friele-MacAdam-Chickering, Version 2, equations based on the MacAdam chromaticity-difference-perceptibility ellipses and the Munsell value function.

foot candle, n – unit of illuminance equal to one lumen per square foot.

Gardner color scale, n –a color scale for clear, light-yellow fluids, defined by the chromaticities of glass standards numbered from 1 for the lightest to 18 for the darkest.

gloss, n – angular selectivity of reflectance, involving surface-reflected light, responsible for the degree to which reflected highlights or images of objects may be seen as superimposed on a surface.

gloss meter, n – instrument that measures surface-reflected light at defined angles (i.e., 60º, 85º).

gray scale, n -- an achromatic scale ranging from black through a series of successively lighter grays to white. Such a series may be made up of steps that appear to be equally distant from one another (such as the Munsell Value Scale) or may be arranged according to some other criteria such as a geometric progression based on lightness. Such scales may be used to describe the relative amount of difference between two similar colors.

goniospectrophotometer, n – spectrophotometer having the capability of measuring with a variety of illuminating and viewing angles using bidirectional geometry; also known as multi-angle spectrophotometer. Usually used to measure colored samples with great directionality.

haze, n – in reflection, (1) scattering of light at the glossy surface of a specimen responsible for the apparent reduction in contrast of objects viewed by reflection at the surface.  (2) percent of reflected light scattered by a specimen having a glossy surface so that its direction deviates more than a specified angle from the direction of specular reflection.

hiding power, n – (1) the ability of a coating material to hide the surface coated by producing a specified opacity at a given film thickness. The greater the amount of scattering pigments, the greater the hide. (2) the area over which a specified volume of paint can be spread to produce a specified contrast between areas where the substrate is black and where it is white.

hue, n -- the attribute of color by means of which a color is perceived to be red, yellow, green, blue, purple, etc. Pure white, black, and grays possess no hue.

Hunter color difference, n – color difference calculated by the use of the Hunter equations, based on the opponent-color coordinates, L, a, b, applied to CIE 1931 tristimulus values for CIE standard illuminant C, and by extension to the CIE 1964 standard observer and other CIE standard illuminants.

illuminant, n -- mathematical description of the relative spectral power distribution of a real or imaginary light source, that is, the relative energy emitted by a source at each wavelength in its emission spectrum (the data entered into a color computer, used to predict the effect of different light sources on the perceived color).

illuminant A (CIE), n -- incandescent illumination, yellow orange in color, with a correlated color temperature of 2856K. It is defined in the wavelength range of 380-770 nm.

illuminants D (CIE), n -- daylight illuminants, defined from 300-830 nm, the UV portion 300-380 nm being necessary to describe correctly colors which contain fluorescent dyes or pigments. They are designated as D with a subscript to describe the correlated color temperature: D65 having a correlated color temperature of 6504K, close to that of Illuminant C, is the most commonly used. They are based on actual measurements of the spectral distribution of daylight.

illuminator, n – the portion of a radiometric or photometric instrument that provides the illuminating beam on the specimen, including the source, occasionally the monochromator or spectral filters, a diffuser such as an integrating sphere, if used, and associated optics.

index of refraction, n – the numerical expression of the ratio of the velocity of light in a vacuum to the velocity of light in a substance (gas, liquid, solid), at a specified wavelength.

integrating sphere, n – an optical device used either to collect light reflected or transmitted from a specimen into a hemisphere or to provide isotropic irradiation of a specimen from a complete hemisphere, consisting of an approximately spherical cavity with apertures (ports) for admitting and detecting light, and usually having additional apertures over which sample and reference specimens are placed and for including or excluding the specularly reflected components (surface reflected light).

interference filter, n – filter constructed of extremely thin alternate layers of high and low refractive-index material and capable of transmitting narrow spectral bands formed by constructive interference within the desired waveband and destructive interference at other wavelengths (used in filter colorimeters and some abridged spectrophotometers).

just-perceptible difference, n – color difference that is just large enough to be perceived by an observer in almost every trial.

Kubelka-Munk theory, n – phenomenological turbid-medium theory relating the reflectance and transmittance of scattering and absorbing materials to optical constants (Kubelka-Munk absorption coefficient (K), Kubelka-Munk scattering coefficient (S)) and the concentrations of their colorants. (The basis of computer color-matching calculations

LED, light emitting diode, n - solid state light emitters that are extremely stable and durable, the latest technology in color instrument light sources.

light, n -- (1) electromagnetic radiation of which a human observer is aware through the visual sensations that arise from the stimulation of the retina of the eye. This portion of the spectrum includes wavelengths from about 380 nm to 780 nm. Thus, it is incorrect to speak of ultraviolet or infrared "light" because the human observer cannot see radiant energy in the ultraviolet and infrared regions. (2) light, adj – referring to the color of a non-self-luminous body, having a high luminous reflectance factor, as "light green" or "light gray."

lightfastness, n – the ability of a material to withstand color change on exposure to light.

lightness, n – (1) the attribute of color perception by which a non-self-luminous body is judged to reflect more or less light.  (2) the attribute by which a perceived color is judged to be equivalent to one of a series of grays ranging from black to white.

light source, n -- an object that emits light or radiant energy to which the human eye is sensitive. The emission of a light source can be described by the relative amount of energy emitted at each wavelength in the visible spectrum, thus defining the source as an illuminant, or the emission may be described in terms of its correlated color temperature.

Lovibond tintometer, n – instrument for evaluating the colors of materials by visual comparison with the colors of glasses of the Lovibond color system.

luminescence, n – emission of light ascribable to nonthermal excitation.

luster, n – the appearance characteristic of a surface that reflects more in some directions than it does in other directions, but not of such high gloss as to form clear mirror images.

masstone, n – in paint technology, a pigment-vehicle mixture containing a single colorant only.

Discussion At times colorants are developed or recycled that contain more than one pigment, but that are tested and used as if they contained only a single pigment. This definition is meant to include such colorants.

match, vt – to provide, by selection, formulation, adjustment, or other means, a trial color that is indistinguishable from, or within specified tolerances of, a specified standard color under specified conditions.

matte, n – lacking luster or gloss. Synonymous with "flat" in paint terminology.

metameric, adj – (1) pertaining to spectrally different objects or color stimuli that have the same tristimulus values. (2) pertaining to objects, having different spectrophotometric curves that match when illuminated by at least one specific  illuminant (viewing condition) and observed by a specific observer.

metamerism, n – property of two specimens that match under a specified illuminator (illuminant) and to a specified observer and whose spectral reflectances or transmittances differ in the visible wavelengths and may appear to be a miss match under a second specified illuminant to the same specified observer.

Munsell color system, n – a system of specifying colors of surfaces illuminated by daylight and viewed by an observer adapted to daylight, in terms of three attributes: hue, value, and chroma, using scales that are perceptually approximately uniform.

Munsell notation, n – (1) the Munsell hue, value, and chroma assigned to the color of a specimen by visually comparing the specimen to the chips in the Munsell Book of Color.  (2) a notation in the Munsell color system, derived from luminous reflectance Y and chromaticity coordinates x and y in the 1931 CIE system for standard illuminant C, by the use of scales defined by the Optical Society of America Subcommittee on the Spacing of the Munsell Colors.

Natural Color System, n – color order system based on resemblance’s of colors to up to four of six "elementary" colors red, yellow, green, blue, black, and white, in which the attributes of the colors are hue, chromaticness, and blackness.

neutral, adj – achromatic or without hue.

observer, n -- the human viewer who receives a stimulus and experiences a sensation from it. In vision, the stimulus is a visual one and the sensation is an appearance.

observer metamerism, n – the property of specimens having different spectral characteristics and having the same color when viewed by one observer, but different colors when viewed by a different observer under the same conditions.

opacity, n – (1) optical, the ability of a specimen to prevent the transmission of light; the reciprocal of the transmittance factor.  (2) paper backing, the ability of a sheet of paper to hide a surface behind and in contact with it, expressed as the ration of the reflectance factor Rb when the sheet is backed by a black surface to the reflectance factor Roo when it is backed by a pile of sheets of the same kind, and of such number that further addition of sheets does not affect the measured opacity.  (3) white backing, the ability of a thin film or sheet of material, such as paint or paper, to hide a surface behind and in contact with it, expressed as the ratio of the reflectance factor Rb when the material is backed by a black surface to the reflectance factor Rw when it is backed by a white surface (usually having a reflectance factor of 0.89.)

opaque, adj – transmitting no optical radiation, you can not see through the material.

opponent-color scales, n – scales that denote one color by positive scale values, the neutral axis by zero value, and an approximately complementary color by negative scale values. Common examples include scales that are positive in the red direction and negative in the green direction (CIE a*, Hunter a) and scales that are positive in the yellow direction and negative in the blue direction (CIE b*, Hunter b).

orange peel, n – the appearance of irregularity of a surface resembling the skin of an orange, usually on painted surfaces.

pearlescent, adj – a colorant exhibiting various colors depending on the angles of illumination and viewing, as observed in mother-of-pearl.

petroleum color scale, n – a color scale for petroleum products, defined by 16 glass standards of specified luminous transmittance and chromaticity, graduated in steps of 0.5 from 0.5 for the lightest color to 8.0 for the darkest.

photochromism, n – a reversible change in color of a specimen due to exposure to light.

photometer, n – an instrument for measuring light.

photopic, adj – pertaining to human vision at sufficiently high levels of illumination that only the retinal cones are stimulated.

physical standard, n – stable specimen having a value of a physical quantity assigned by accurate measurements under specified conditions, usually in a standards laboratory.

port, n – an opening or aperture in an integrating sphere.

precision, n – the closeness of agreement between test results obtained under prescribed conditions.

primary colorants, n – a small number (pallet) of colorants (dyes or pigments) that may be mixed to produce a large gamut of colors.

primary standard, n – a physical standard calibrated by an absolute method.

product standard, n – material having a color designated as standard for a specified product.

radiant energy, n -- the form of energy consisting of the electromagnetic spectrum that travels at 115.890 kilometers/s (186.500 miles/s) through a vacuum, reducing this speed in denser media (air, water, glass, etc.). The nature of radiant energy is described by its wavelength or frequency, although it also behaves as distinct quanta ("corpuscular theory"). The various types of energy may be transformed into other forms of energy (electrical, chemical, mechanical, atomic, thermal, radiant) but the energy itself cannot be destroyed.

receiver, n – the portion of a photometric instrument that receives the viewing beam from the specimen, including a collector such as an integrating sphere, if used, often the monochromator or special filters, the detector, and associated optics and electronics.

reference standard, n – a physical standard used to calibrate a group of laboratory standards.

reflectance, n -- the ratio of the intensity of reflected radiant flux to that of the incident flux. In popular usage, it is considered as the ratio of the intensity of reflected radiant energy to that reflected from a defined reference standard.

reflectance, specular, n -- reflectance of a beam of radiant energy at an angle equal but opposite to the incident angle: the mirror-like reflectance. The magnitude of the specular reflectance on glossy materials depends on the angle and on the difference in refractive indices between two media at a surface and may be calculated from the Fresnel Law.

reflection, n – of radiant energy (in the case of color, light), the process by which radiant energy is returned from a material or object.

refraction, n – change in the direction of light determined by change in the velocity of the light in passing from one medium to another.

repeatability, n – (1)  the closeness of agreement between the results of successive measurements of the same test specimen, or of test specimens taken at random from a homogeneous supply, carried out on a single laboratory, by the same method of measurement, operator, and measuring instrument, with repetition over a specified period of time. This is the most important  aspect of sample presentation technique and   one of the most important specifications for a color instrument. (2) the ability to create and replicate a formula in a consistent manner as defined by a defined tolerance.

reproducibility, n – the closeness of agreement between the results of successive measurements of the same test specimen, or of test specimens taken at random from a homogeneous supply, but changing conditions such as operator, measuring instrument, laboratory, or time. The changes in conditions must be specified.

retroreflector, n – a reflecting surface or device from which, when directionally irradiated, the reflected rays are preferentially returned in directions close to the opposite of the direction of the incident rays, this property being maintained over wide variations of the direction of the incident rays. Most commonly used in highway signage materials.

saturation, n -- the attribute of color perception that expresses the degree of departure from the gray of the same lightness. All grays have zero saturation. Commonly used as a synonym for chroma especially in graphic arts.

scattering, n -- diffusion or redirection of radiant energy encountering particles of different refractive index; scattering occurs at any such interface, at the surface, or inside a medium containing particles.

scattering tinting strength, n – relative change in the scattering properties of a standard black material (with no scattering colorant present) when a specified amount of a white or chromatic scattering colorant is added to it.

scotopic, adj – pertaining to vision at sufficiently low levels of illumination that only the retinal rods are stimulated.

shade, n – (1) a color produced by a dye or pigment mixture including black dye or pigment. (2) an expression of color difference from a reference dyeing such that another dye must be added to produce a match. (3) a color slightly different from a reference color.

shade, vt – to adjust the color of a test specimen to be a closer color match to the standard.

shade sorting, n – process of grouping together, often by instrumental measurement, similarly colored materials so that the materials within each group may be used together in a finished product without perceived color variation.

sheen, n – the specular gloss at a large angle of incidence for an otherwise matte specimen (used in textiles).

source, n – an object that produces light or other radiant flux.

spectral, adj – for radiometric quantities, pertaining to monochromatic radiation at a specified wavelength or, by extension, to radiation within a narrow wavelength band about a specified wavelength.

spectral characteristic, n – the reflectance, reflectance factor, transmittance, or transmittance factor as a function of wavelength, used to characterize a specimen.

spectral power distribution curve, n -- intensity of radiant energy as a function of wavelength, generally gives in relative power terms.

spectrocolorimeter, n – spectrophotometer, one component of which is a dispersive element (such as prism, grating, or interference filter or wedge) that is normally capable of producing as output only colorimetric data (such as tristimulus values and derived color coordinates) but not the underlying spectral data from which colorimetric data are derived.

spectrogoniophotometer, n – goniophotometer having the capability of measuring as a function of wavelength. See the preferred term, goniospectrophotometer.

spectrometer, n – an instrument for measuring a specified property as a function of a spectral variable. In optical radiation measurements, the spectral variable is wavelength or wavenumber and the measured property is (or is related to) absorbed, emitted, reflected, or transmitted radiant power.

spectrophotometer, n -- photometric device for the measurement of spectral transmittance, spectral reflectance, or relative spectral emittance.

spectrophotometry, n – quantitative measurement of reflection or transmission properties as a function of wavelength.

spectroradiometer, n – a spectrometer for measuring emitted optical radiant power, normally of a light source.

Spectrum Spatial arrangement of components of radiant energy in order of their wavelengths, wave number or frequency.

spectrophotometric curve, n -- a curve measured on a spectrophotometer: hence a graph of relative reflectance or transmittance (or absorption) as the ordinate, plotted versus wavelength or frequency as the abscissa. In color, usually covering the practical visual range from 400-700 nm.

specular, adj – pertaining to flux (light) reflected from the surface of an object, without diffusion, at the specular angle.

specular gloss, n -- relative luminous fractional reflectance from a surface in the mirror or specular direction. It is sometimes measured at 60° relative to a perfect mirror.

specular reflection, n – reflection without diffusion, in accordance with the laws of optical reflection, as in a mirror.

specular reflectance excluded (SCE), n -- measurement of reflectance made in such a way that the specular reflectance is excluded from the measurement: diffuse reflectance. The exclusion may be accomplished by using 0º (perpendicular) incidence on the samples, thereby reflecting the specular component of the reflectance back into the instrument, by use of black absorbers or light traps at the specular angle when the incident angle is not perpendicular, or in directional measurement by measuring at an angle different from the specular angle. Used where surface finish is an important component of a color measurement.

specular reflectance included (SCI), n -- measurement of the total reflectance from a surface, including the diffuse and specular reflectance (usually in a sphere instrument). Used when the surface finish is not critical to color measurement results.

standardize, vt – to adjust instrument output to correspond to a previously established calibration using one or more homogeneous specimens or reference materials. (calibrate, verify) This is the normal condition that is often referred to as "field calibration" of a color instrument.

standard observer, n – an ideal observer having visual response described by the CIE color-matching functions.

strength, n – (1) the color quality that increases with an increase in the amount of colorant present, other conditions remaining constant. (2) in reflection colorants, a series of calculations based on the relative absorption of a given colorant.

subtractive color mixture, n – mixture of absorbing media or superposition of filters so that the spectral composition of light passing through the combination is determined by simultaneous or successive absorption.

surround, n – portion of the visual field immediately surrounding the central field or pattern of interest.

texture, n – the visible surface structure depending on the size and organization of small constituent parts of a material; typically, the surface structure of a woven fabric or surface finish of a painted part.

thermochromism, n – a change in color with temperature change. adj - thermochromatic

tint, n -- the color produced by the mixture of white pigment with absorbing (generally chromatic) colorants. The color of the resulting mixture is lighter and less saturated than the color without the addition of the white.

tint, vt – to adjust the color of a test specimen to be a closer color match to the standard.

tolerance, n - the range of color difference that is acceptable to say that the color is a commercial match. Most usually an agreement  is made between buyer and seller concerning color acceptability.

transfer standard, n – a physical standard used to transfer a calibration from one instrument to another, usually from a reference instrument in a standards laboratory to an instrument in the field.

translucency, n – the property of a specimen by which it transmits light diffusely without permitting a clear view of objects beyond the specimen and not in contact with it.

translucent, adj – transmitting light diffusely, but not permitting a clear view of objects beyond the specimen and not in contact with it.

transmission, n – of radiant energy, the process whereby radiant energy passes through a material or object.

transparency, n – the degree of regular transmission, thus the property of a material by which objects may be seen clearly through a sheet of it.

transparent, adj -- adjective to describe a material that transmits light without diffusion or scattering.

tristimulus, n -- of, or consisting of, three stimuli: generally used to describe components of additive mixture required to evoke a particular color sensation.

tristimulus values,match n – the amounts of the three specified human response stimuli required to match a color.

tristimulus values, CIE, n -- amounts (in percent) of the three components necessary in a three-color additive mixture required for matching a color; in the CIE System, they are designated as X, Y and Z. The illuminant and standard observer color matching functions used must be designated; if they are not, the assumption is made that the values are for the 1931 observer (2º field) and Illuminant C. The values obtained depend on the method of integration used and on the relationship of the nature of the sample and on the instrument design used to measure the reflectance or transmittance. Tristimulus values are not, therefore, absolute values characteristic of a sample, but relative values dependent on the method used to obtain them. Approximations of CIE tristimulus values may be obtained from measurements made on a tristimulus colorimeter, giving measurements generally normalized to 100, which must then be normalized to equivalent CIE values. The filter measurements should be properly designated as R, G, and B instead of X, Y, and Z.

tungsten, light source, n - (1) constant burning tungsten, traditional light source in color instruments.                    (2) flashing tungsten, latest low cost light source, typically used in portable color instruments.

turbidity, n – reduction of transparency of a specimen due to the presence of particulate matter.

ultraviolet, adj – referring to radiant flux having wavelengths shorter than the visible wavelengths, about 10 nm to 380 nm.

uniform-chromaticity-scale diagram, n – chromaticity diagram on which all pairs of just-perceptibly different colors of equal luminance are represented by pairs of points separated by nearly equal distances.

uniform color space, n – schematic arrangement of colors in space in which spatial intervals between points correspond to visual differences between colors represented by those points (goal of all color space/order systems that has yet to be achieved).

verification standard, n – calibrated physical standard used to verify the accuracy of calibration of measurement scales, operating characteristics, or system responses of color-measuring instruments.

verify, vt – to assess the overall reliability and accuracy of an instrument or method of measurement by use of material standards for which the measurable quantities have accepted values.

viewing conditions, n – the conditions under which a visual observation is made, including the angular subtense of the specimen at the eye, the geometric relationship of light source, specimen, and eye, the photometric and spectral character of the light source, the photometric and spectral character of the field of view surrounding the specimen, and the state of adaptation of the eye.

visible, adj – pertaining to that portion of the electromagnetic spectrum to which the eye is sensitive, approximately 390 to 710 nm in wavelength.

visibility, n – the properties and behavior of light waves and objects interacting in the environment to produce light signals capable of evoking visual sensation.

visual colorimeter, n – an instrument using the eye as detector that measures color stimuli produced by mixing one or more of at least three primary colors.

visual perception, n – the visual experience resulting from stimulation of the retina and the resulting activity of associated neural systems.

wavelength, (y), n – of an electromagnetic wave, the distance in the direction of propagation between nearest points at which the electric vector has the same phase; the distance as expressed in nanometers (nm, billionth of a meter) of the wavelength period or frequency (peak to peak or trough to trough) of the wavelength in question. The visible spectrum spans 400-700m.

whiteness, n – attribute of color perception by which an object color is judged to approach the preferred white.

whiteness index, n – a number, computed by a given procedure from colorimetric data that indicates the degree of departure of an object color from a preferred white.

working standard, n – (1) an instrument standard or laboratory standard in routine use. (2) a standard that is almost identical to the laboratory standard and the color difference is exaclty known  from the  laboratory standard.

xenon, light source, n - high energy, pulsed light used in color instruments.

yellowness, n – attribute of color perception by which an object color is judged to depart from colorless or a preferred white toward yellow.

yellowness index, n – a number, computed by a given procedure from colorimetric or spectrophotometric data that indicates the degree of departure of an object color from colorless, or from a preferred white, toward yellow.

X One of the three CIE tristimulus values; the red primary.

Y One of the three CIE tristimulus values; equal to the luminous reflectance or transmittance ; the green primary

One of the three CIE tristimulus values; the blue primary.