This international Standard specifies the characteristics of the system of physical photometry established by the CIE and accepted as the basis for the measurement of light. It defines the photometric quantities, units and standards that make up the CIE system of physical photometry and that have been officially accepted by the Comité International des Poids et Mesures (CIPM). They comprise: — the definition of photometric quantities and units, — the definition of CIE standard spectral luminous efficiency functions for photopic and scotopic vision, — the definition of a CIE standard photometric observer that conforms to these functions, — the definition of maximum luminous efficacies for photopic and scotopic vision. An informative annex provides a vocabulary of related terms.