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 observerThis 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 observerThis set of colour-matching functions is representative of the colour-matching properties of observers with normal colour vision f