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This International Standard specifies colour-matching functions for use in colorimetry. Two sets of colour-matching functions are specified. a) Colour-matching functions for the CIE 1931 standard colorimetric observer This set of colour-matching functions is representative of the colour-matching properties of observers with normal colour vision for visual field sizes of angular subtense from about 1° to about 4°, for vision at photopic levels of adaptation. b) Colour-matching functions for the CIE 1964 standard colorimetric observer This set of colour-matching functions is representative of the colour-matching properties of observers with normal colour vision for visual field sizes of angular subtense greater than about 4°, for vision at sufficiently high photopic levels and with spectral power distributions such that no participation of the rod receptors of the retina is to be expected.