The author discusses on the physical meanings of the different definitions of the colour temperature and advises to use in photometry, radiometry and optical pyrometry the definition which is based upon the analogy of the spectral energy distribution curve of the light source to that of the black body and is called as the distribution temperature (Verteilungsternperatur in Germany).
Moreover, he recommends to indicate the distribution temperature of the source with a certan region of wavelength in which the identity of its distribution curve to that of the black body is approved under the considered accuracy.
The author describes a plan to establish the distribution temperature scale, that is, to measure the relative spectral energy distributions of the tungsten ribbon filament lamps choosen as its substandards comparing with a carbon tube black body furnace constructed recently in his Electrotechnical Laboratory.
