The Physikalisch-Technische Bundesanstait (PTB), Germany's national metrology institute, has been operating a radiometry laboratory at the BESSY I 800 MeV electron storage ring since 1982. BESSY I 800 is used as a primary source standard of calculable spectral photon flux with relative uncertainties below 0.4% in a broad spectral range from 1 eV to 15 keV. A cryogenic electrical-substitution radiometer is operated as a primary detector standard with a relative uncertainly of less than 0.2% in the measurement of radiantion power. Based on these primary standards, radiation sources, detectors and optical components are characterized and calibrated at various experimental stations. Currently, PTB is commissioning new experimental stations in its radiometry laboratory at the third generation BESSY II 1.7 GeV electron storage ring to extend the spectral range to the hard X-ray range by using radiation from bending magnets and a superconducting wavelength shifles, and to improve radiometry by using undulator radiation. The current status of radiometry at BESSY I will be reviewed and the new radiometry programs outlined which have been planned for BESSY II.
