Calibration standards for spectral radiance and spectral irradiance are disseminated in the form of transfer lamps and integrating sphere sources. These disseminated standards are made traceable to the SI. Continuous effort is made to improve the transfer standards and procedures to lower the total uncertainties. The NIST spectral radiance and spectral irradiance scales are periodically compared against other national laboratories in international comparisons sponsored by the Consultative Committee on Photometry and Radiometry (CCPR).
The spectral radiance sources in the form of tungsten-strip lamps and integrating-sphere sources are calibrated in the Facility for Spectroradiometric Calibrations (FASCAL). The measurements are performed by the use of a prism-grating double monochromator whose spectral radiance responsivity is determined using a variable-temperature blackbody. The temperature of this blackbody is determined using the gold-point blackbody and spectral radiance sources are calibrated using the knowledge of the temperature of the blackbody and the Planck radiation law.
The FASCAL 2 facility is solely dedicated to spectral irradiance scale realizations and calibrations. The spectral irradiance standards are calibrated using a high-temperature blackbody operating at nearly 3000 K. The temperature of the blackbody is determined using detector-based techniques traceable to the SIRCUS facility and the spectral irradiance responsivity of a double-grating monochromator is calibrated.
The spectral irradiances of deuterium lamps from 200 nm to 400 nm are calibrated in the Facility for Irradiance Calibration Using Synchrotrons (FICUS) which is located in the Synchrotron Ultraviolet Radiation Facility (SURF).