Tungsten lamp as radiation standard and the emissivity effects

The derivative of the detected incidance in a wavelength interval with respect to temperature has previously been shown to include two terms. The first term depends on the change in the blackbody emission with temperature. The second term depends on the change of emissivity with temperature. The error of neglecting the second terms is analyzed and evaluated for a standard radiation source, a tungsten lamp, for which the measured emissivity data have been published. In this specific case the error changes form a negligible 6% to a significant value of more than 45%.