The Spectral Emissivity and the Relation of True Temperatures and Brightness Temperatures of Platinum

Spectral emissivities of platinum for λ=660 mμ have been measured by using an optical pyrometer to compare the brightness of the surface of an incandescent tubular filament with that of a small hole through the wall of the tube. They have been used to compute true temperature as a function of brightness temperature, for the range 1200°K to 1900°K true temperature. The emissivity was found to vary linearly with temperature, from 0.283 at 1200°K to 0.295 at 1900°K. The brightness of an incandescent platinum surface was found to vary with angle of emission rising to a maximum 1.24 times the normal brightness at an emission angle of 80° and decreasing thereafter.