PTB network for realization and maintenance of the candela

The paper describes the main steps in the realization of the Système International d'Unités (SI) base unit of luminous intensity, the candela, at the Physikalisch-Technische Bundesanstalt (PTB). The realization, using incandescent lamps, is based on radiant power measured with absolute radiometers. Transfer to other lamps is done by V (λ)-corrected detectors. The lamps are grouped according to their distribution temperature. These groups of lamps and a group of V (λ)-corrected detectors are combined to form a network for the maintenance and dissemination of the unit with a reduced uncertainty. The network presented in detail here ensures excellent continuity of the maintained unit.