metrologia International comparison of radiation-temperature measurements with ®ltered detectors over the temperature range 1380 K to 3100 K N. J. Harrison, N. P. Fox, P. Sperfeld, J. Metzdorf, B. B. Khlevnoy, R. I. Stolyarevskaya, V. B. Khromchenko, S. N. Mekhontsev, V. I. Shapoval, M. F. Zelener and V. I. Sapritsky Abstract. A series of black-body radiation-temperature measurements has been made over the temperature range 1380K to 3100 K using two different designs of pyrolytic-graphite black bodies with calculated emissivities of 0.999. All measurements were performed at the All-Russian Research Institute for Optophysical Measurements (VNIIOFI) during June 1997. A ®lter photometer from the VNIIOFI, broadband glass-®lter detectors from the Physikalisch-Technische Bundesanstalt (PTB) and narrowband interference-®lter-based radiometers from the National Physical Laboratory (NPL) were used to perform the temperature measurements in either radiance or irradiance mode using both black bodies. Across the entire temperature range, the NPL and PTB instruments showed consistent results with both black bodies and differing geometrical arrangements. Results from the VNIIOFI photometer were also broadly consistent for a wide temperature range. 1. Introduction Spectral emission scales being established by several major national standards institutions [1-3] rely on the application of Planck’s black-body equation to predict the spectral distribution from a cavity radiator that is a close approximation to an ideal black-body source. The use of Planck’s black-body equation is dependent on accurate knowledge of the radiation temperature of the source. Determination of the radiation temperature is usually accomplished by measuring the radiance or irradiance from the black body using a calibrated ®lter and detector combination over a speci®c wavelength band. The ®ltered detector is calibrated against a cryogenic radiometer, linking emission scales to an absolute detector [4-6]. Con®dence in the derived spectral-emission scales can only be obtained after measurements are made of N. J. Harrison and N. P. Fox: Centre for Optical and Environmental Metrology, National Physical Laboratory (NPL), Teddington, Middlesex TW11 0LW, UK. P. Sperfeld and J. Metzdorf: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany. B. B. Khlevnoy, R. I. Stolyarevskaya, V. B. Khromchenko, S. N. Mekhontsev, V. I. Shapoval, M. F. Zelener and V. I. Sapritsky: All-Russian Research Institute for Optophysical Measurements (VNIIOFI), 46 Ozernaya, Moscow 119361, Russian Federation. the black body at several different wavelength points across the spectrum to verify that the cavity is a good approximation to a true black body over the spectral region of interest. Variation in the emissivity of graphite or pyrolytic graphite, common construction materials for black bodies, with wavelength and the non-ideal distribution of cavity surface temperature, make this veri®cation check a necessity. Filtered detectors or ®lter radiometers have therefore been constructed by national standards institutions at many different wavelengths for the measurement of radiation temperature, each instrument being calibrated against national detector- responsivity scales. In June 1997, at the VNIIOFI in Moscow, an international comparison of radiation-temperature measurement took place between the VNIIOFI, the PTB and the NPL as part of an international collaboration to realize the unit of luminous ¯ux, the lumen. This project is based on the use of a state-of-the-art black body, developed at the VNIIOFI, to act as the optical radiation source for the lumen realization. Initially it was necessary to investigate the performance and characteristics of two different designs of black body to verify their suitability for use in the experiment. Measurements of uniformity of radiance and irradiance were therefore performed on both designs and the results are given in another paper in this journal [7]. Metrologia, 1998, 35, 283-288 283