I

ICC
The International Color Consortium.

Illuminant
Light specified by its spectral distribution, used to illuminate, but may be defined theoretically for computation purposes and may not correspond to a real light source.

Illuminance
Luminous flux incident per unit of area.

Achromatic
A colour perceived as having no hue, that is, as white, black or grey.

Illuminant A (CIE)
CIE Standard Illuminant for a Tungstem illumination, yellowish in colour. Has a correlated colour temperature of 2856°K.

Illuminant B (CIE)
CIE Standard Illuminant that simulates daylight (yellowish in colour) with a correlated colout temerature of 4874°K. No longer in general use.

Illuminant C (CIE)
CIE Standard Illuminant that simulates daylight (blueish in colour) with a correlated colour temperature of 6774°K. Generally replaced by D₆₅ because of illuminant C's deficency in UV.

Illuminants D (CIE)
CIE Standard Illuminants based on actual measurements of daylight. D₆₅ with a correlated colour temperature of 6504°K is the most commonly used. Others include D₅₀, D₅₅ and D₇₅.

Imaginary colours

Incandescence
The emission of luminous flux (glowing) characteristic of bodies at high temperature.

Incandescent illuminant
Incandescent illuminants produce light by electricaly heating tungsten filaments (eg. Illuminant A).

Infrared
Reffering wavelengths longer than the wavelength of visible light. Usually wavelengths from above 760 nm to about 3mm.

Ingling colour-vision model

Integrating sphere

Internal reflection

Intensity (luminous)
The light flux per unit solid angle.

Intensity (radiant)
The radiant flux per unit solid angle.

Internal absorptance

Irradiance

Irradiance (spectral)

ISCC-NBS
A name for a colour, defined in terms of the Munsell colour order space, using a system developed cooperatively by the Inter-Society Color Council and the National Bureau of Standards.

Ishihara charts

ISO
The International Standards Organisation.

ISO method of measuring opacity

Isobestic wavelength

Isochromes

Isomerism
Same as metamerism.

Isotemperature lines

Isotropic
The same in all directions.

Iteration
A mathematical technique whereby a solution to a problem is obtained by first making a guess (approximation) at the answer, then, based on the results of this guess, a modified (improved) guess is calculated. This procedure is then repeated until a close enough (if possible) solution is achieved. This method is often used by colorant match prediction software (see Allan algorithm).