Abstract
The emissivity of a high-temperature black body, used for the realization of the spectral irradiance scale at the Physikalisch-Technische Bundesanstalt (PTB), has been examined experimentally by direct reflection measurements. Measurements at two laser wavelengths show a significant dependence on temperature of the normal effective emissivity of the cavity. The emissivity is very close to the ideal value of unity at temperatures above 2000 K. Preliminary experiments on the reflectance and emissivity of graphite, the material from which the black-body cavity is made, were carried out at room temperature. Using the results of these measurements as input parameters for Monte Carlo calculations of the effective emissivity of the cavity, good agreement with the measurements is obtained.
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