spectral mismatch correction factor (for a photometer) [F*]

factor by which the readings of a physical photometer may be multiplied in order to correct for the error caused by differences between the relative spectral responsivity of the photometer and the photometric observer function that it is intended to simulate, when the photometer is used to measure a light source having a relative spectral power distribution different from that of the source with which the photometer was calibrated

Unit: 1

NOTE 1 Most photometers are designed to simulate the V(λ) function and calibrated using a source corresponding to CIE Standard Illuminant A. For such a photometer, the correction factor may be calculated using the equation:


where srel(λ) is the relative spectral responsivity of the photometer and S(λ) and SA(λ) are the respective relative spectral power distributions of the light source to be measured and CIE Standard Illuminant A.

NOTE 2 This correction factor was formerly known as "colour correction factor".

NOTE 3 This term can also be applied to other radiometers whose response is intended to simulate a particular observer function, such as actinic radiometers.

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