Experimental investigation on the establishment of a spectral-radiance scale based on a copper-freezing-point black-body radiator

Abstract

The spectral radiance of a black body can be calculated from Planck's radiation law when the black-body temperature is known. Therefore, the spectral radiance of a black-body radiator of accurately known temperature may be used as a reference for the establishment of a spectral radiance scale. In this paper we investigate the feasibility of using a copper-freezing-point (1357.77 K) black-body radiator to directly calibrate gas-filled tungsten strip-filament lamps operating at a radiance temperature of 2300 K (at 650 nm). A silicon photodetector with a variable-gain amplifier, as well as optical apertures of different sizes, were used to measure the large radiance ratios observed. The comparison was performed at eight wavelengths between 400 nm and 900 nm using interference filters. The major problem encountered was out-of-passband infrared (IR) leakage of the interference filters, particularly those below 550 nm. We discuss the use of sharp-cut glass filters to correct the IR leakage of the filters.