New photometric calibration programmes at the National Institute of Standards and Technology

The National Institute of Standards and Technology (NIST) candela is maintained via standard photometers which have shown long-term stability of better than 0.1 % per year. The detector-based method has allowed us to reduce the uncertainties of calibrations and to expand the range of calibration capabilities. There have been several new developments in photometry at the NIST. A high-illuminance calibration facility has been developed. Four temperature-controlled standard photometers, tested for linearity and thermal effects at high illuminances, are used with a high-pressure xenon arc source to provide the illuminance scale at levels up to 100 klx. A flashing-light photometric unit (lx s) has been realized using four standard photometers equipped with current integrators, and using two independent methods. Calibration services for illuminance meters at high illuminance levels and flashing-light photometers are now available at the NIST. Ongoing new projects include the development of a detector-based luminous-flux calibration facility using a 2.5 m integrating sphere, realization of the total spectral radiant-flux scale, and the development of a reference spectroradiometer for colorimetry of displays. Calibration services are planned in these areas of photometry and colorimetry in the near future.