Absolute radiometry by means of a black body source

Abstract

The use of a black body lamp whose temperature is established by means of optical pyrometry can conveniently provide a standard spectral power distribution that is known in absolute terms. The degree of reproducibility demonstrated in the present work suggests that a practical realization of the candela by this method may be preferable to the conventional approach using freezing platinum. The experiment described interrelates four of the basic scales maintained by the N. P. L. (and other national laboratories): these are the temperature scale, the photometric scale, the colour temperature scale and the radiometric scale. One interpretation of the results is that the freezing temperature of platinum implicit in the photometric scale is about 3K higher than that realized in recent temperature scale work. On the other hand, a previously established relation between the photometric and radiometric scales tends to support the lower value for T Pt .