Principles governing photometry (2nd edition)

This document brings together the definitions and the tables of numerical values for photometry already adopted (or recommended) and published, by the Conference Generale des Poids et Mesures (CGPM), by the Comite International des Poids et Mesures (CIPM), or by the Commission Internationale de l'Eclairage (CIE). This document provides the link between the definition of the candela in the International System of Units (SI) and the internationally agreed spectral luminous efficiency functions for human vision published by the CIE, including those for mesopic vision and for photopic vision for a 10° field of view, in addition to those for photopic vision for a 2° field of view and for scotopic vision. The definitions of photometric units and quantities have also been updated with the reformulated definition of the candela in the International System of Units (SI) 2019 and the latest definitions of the photometric quantities by the CIE.