Tungsten strip lamps are calibrated at specific wavelengths. The calibration at one wavelength can be corrected to make it valid at another wavelength λ for calibrating a radiation thermometer that operates at λ. The correction can be obtained by a calculation based on either Wien's or Planck's radiation law with the knowledge of the spectral emissivity ε of the lamp filament and the spectral transmittance т of the lamp window. Using published measurements of 8 for tungsten and our measurement of т for the window of a high-stability tungsten strip lamp, we develop analytical expressions for ε as a function of wavelength and temperature and for т as a function of wavelength. These allow accurate calculations of the spectral dependence of the radiance temperature of such a lamp, from which the appropriate corrections can be made. Results are presented.
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