ISO/CIE 23539:2023

This document 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). This comprises:
—    the definition of photometric quantities, symbols and units;
—    the definition of CIE spectral luminous efficiency functions for photopic vision, scotopic vision, mesopic vision and 10° photopic vision;
—    the definition of CIE photometric observers that conforms to these functions;
—    the definition of maximum luminous efficacy for photopic vision, mesopic vision, scotopic vision and 10° photopic vision.