[] \overline{x}=x_{\lambda }/\Phi _{e\lambda };\overline{y}=y_{\lambda }/\Phi _{e\lambda };\overline{z}=z_{\lambda }/\Phi _{e\lambda }
The tristimulus values per unit wavelength interval and unit spectral radiant flux.


(i) Color matching functions have been adopted by the International Commission on Illumination (CIE). They are tabulated as functions of wavelength throughout the spectrum and are the basis for the evaluation of radiant energy as light and color. The standard values adopted by the CIE in 1931 are given in Table 13.5A. The values are identical with the values of spectral luminous efficiency for photopic vision (see values of spectral luminous efficiency for photopic vision and Table 13.4).

(ii) The \overline{x},\overline{y},\overline{z} values for the 1931 Standard Observer are based on a two-degree bipartite field, and are recommended for predicting matches for stimuli subtending between one and four degrees. Supplementary data based on a ten-degree field were adopted in 1964 for use for angular subtends greater than four degrees (see Table 13.5B). Tristimulus computational data for CIE standard source C are given in Table 13.6.

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