The Suitability of Tungsten Strip Lamps as Secondary Standard Sources below 1064°C

High-stability tungsten strip lamps are assessed as a means of maintaining the International Practical Temperature Scale below 1064.43°C. The variation of spectral radiance temperature with changes in the lamps and their environment is discussed. Factors necessary to correct the spectral radiance temperature for changes in the resistance and pin temperature of two lamps are given. It is shown that applying corrections for changes in lamp resistance reduces the uncertainty in the use of lamps by an order of magnitude. The uncertainties which are to be associated with the use of tungsten strip lamps under practical conditions are 0.015°C at 1064°C and 0.045°C at 770°C (99% confidence limits). These results indicate that the platinum resistance thermometer appears to be a better alternative means of maintaining temperature scales in the range considered.