The spectral luminous efficiency function for photopic vision. It was adopted in 1924 by the International Commission on Illumination (CIE) and in 1970* by the International Committee of Weights and Measures (CIPM). It is based on a 2° viewing field and principles of heterochromatic photometry and was incorporated into the CIE 1931 Colorimetric Observer as the ȳ function.
Unless otherwise indicated, the values used for spectral luminous efficiency in photopic vision are the values agreed upon internationally in 1924 by the CIE, completed by interpolation and extrapolation, and recommended by the CIPM in 1972.
NOTE: This term and its definition were changed in RP-16-17 Addendum 1.
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