ISO 23539:2005 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).
BS ISO 23539:2006 history
2006BS ISO 23539:2006 Photometry - The CIE system of physical photometry