Standard spectral power distributions

A tungsten lamp of known colour temperature and intensity may conveniently be used as a standard of spectral power distribution. This paper describes a method of calculating absolute values of spectral radiant intensity using the two known parameters. The tables, which are based on De Vos' values for the emissivity of tungsten, list the spectral radiant intensity per candela Q (λ) for both tungsten and blackbody sources in μW sr −1 cd −1 Δλ −1 for a 10 nm wavelength interval. Specimen tables are reproduced for the three temperatures 2043·2, 2700 and 2855·54 K. Q (λ) is given at 10 nm intervals over the range 240 to 830 nm and at wider intervals to 2600 nm. The accuracy attainable by this method is about ±1% at the centre of the visible spectrum.