Factors affecting the Reproducibility of Brightness of Tungsten Strip Lamps for Pyrometer Standardization

Abstract

A quantitative examination is made of the effect of the experimental conditions on the apparent brightness of tungsten strip lamps when used for pyrometer standardization. It is shown that unless certain precautions are observed appreciable differences in brightness may occur as a result of gradients of temperature in the lamp filament and of ambient temperature changes. Owing to the incidence of the Thomson effect it is important to ensure that a consistent lamp polarity is maintained. The effect of reflexions from the glass envelope of the lamp is considered and the most satisfactory sighting conditions determined to minimize this effect. In a gas-filled lamp it is seen that the presence of convective cooling of the filament necessitates precise positioning of the lamp relative to the vertical.