17-341

distribution temperature (of a source in a given wavelength range, λ1 to λ2) [TD]

temperature of the Planckian radiator whose relative spectral distribution S(λ) is the same or nearly the same as that of the radiation considered in the spectral range of interest for which the following integral is minimized by adjustment of a and T:

        

where λ is the wavelength, St(λ) is the relative spectral distribution of the radiation being considered, Sb(λ, T) is the relative spectral distribution of the Planckian radiator at temperature T, and a is a scaling factor

Unit: K

NOTE 1 Planck's radiation formula:

        

where c2 is the second radiation constant.

NOTE 2 Distribution temperature is a meaningful characteristic for radiators having a relative spectral distribution similar to that of a Planckian radiator, but only if calculated for an extended wavelength range and for radiation whose spectral power distribution is a continuous function of wavelength in that range.

NOTE 3 In photometry and colorimetry this wavelength range, λ1, λ2, is the visible spectral region and in these cases the range from λ1 = 400 nm to λ2 = 750 nm is recommended.

NOTE 4 In practice, the integral is replaced by a summation. For incandescent lamps, equally spaced wavelength intervals of 10 nm will usually suffice. All values in the summation are treated with equal weight.

See also CIE 114-1994 CIE Collection in Photometry and Radiometry - 114/4 Distribution Temperature and Ratio Temperature

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