A phenomenon whereby the nature of the colour difference between two similarly coloured objects, changes with change in the spectral distribution (characteristics) of the illuminant.
Note 1: Metamerism is most frequently seen when two coloured objects match in daylight, but differ markedly in colour when viewed in tungsten-filament light. This arises because the visible absorption spectra of the two objects differ significantly, although the tristimulus values in daylight are identical.
Note 2: This term is often used loosely to describe the behaviour of a single coloured object that shows a marked change of colour as the illuminant changes. Use of this term in this way is incorrect: this effect should be described as lack of colour constancy
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