Abridged Spectrophotometer (VIS): 
A spectrophotometer that uses a set of colour filters to define relatively broadband wavelength intervals in the visible spectrum.

Absorbance: 
see Optical Density.

Absorption:
The transformation of radiant energy to a different form of energy by interaction.

Absorptance:
The ratio of absorbed radiant flux to the incident flux.

Brightness:
The quantity of light reflected (a bright colour reflects more light whereas a dim colour reflects less).

Chroma:
see Saturation.

Chromatic:
Perceived as having a hue; not white, grey or black.

Chromaticity:
Chromaticity is that part of a colour specification that does not involve the amount of light energy; it is specified by pairs of chromaticity co-ordinates or dominant wavelength and purity.

Chromaticity coordinates:
The ratio of each of the tristimulus values of a colour to the sum of the tristimulus values (designated x, y, z in the CIE system).

CIE, Commission Internationale de l’Eclairage: 
the international organisation concerned with light, vision and colour.

Comparator:
An instrument that relies on a comparison between a coloured sample and a suitable range of colour standards under specified conditions.

Colorimeter:
An instrument which relies on a match between a coloured sample and a stimulus produced by mixing a suitable combination of one or more, of at least three, primaries.

Colour difference:
The magnitude of the difference between two object colours under specified conditions.

Colour grading:
Identifying a sample by a colour grade or score which is specific to the colour or the material graded

Colour matching:
Procedure for providing a trial colour which is indistinguishable, within a specified tolerance, from a reference colour

Colour measurement:
Process of deriving, by visual or electronic means, a set of numbers that describe the attributes of a colour

Hue or colour:
The type of colour, whether it is red, blue, green or purple etc.

Optical density:
Logarithm to the base 10 of the reciprocal of the transmittance.

Photometer:
An instrument that measures the relative amount of light transmitted by, or reflected from, a sample in a defined wavelength interval in the visible spectrum.

Saturation or chroma:
Refers to the strength or amount of the hue - how much the full hue is desaturated with white.

Spectrophotometer (VIS):
An instrument that measures the relative amount of light transmitted by, or reflected from, a sample in a small wavelength interval at each wavelength in the visible spectrum.

Spectrophotometry: 
Measurement of the relative amounts of radiant flux at each wavelength of the spectrum.

Standard Illuminants:
Relative spectral power distributions defining illuminants for use in colorimetric computations.

Transmission:
Passage of radiation through a medium without change of frequency.

Transmittance:
The ratio of transmitted flux to incident flux under specified conditions.

Tristimulus Colorimeter:
An instrument with spectral response functions that are directly proportional to the colour matching functions of the CIE Standard Colorimetric Observer.

Tristimulus Values:
The amounts of three specified stimuli required to match a colour.

Turbidity:
Reduction of transparency of a specimen due to the presence of particular matter.

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