The spectral output quantity of a system such as a photomultiplier, diode array,
photoimaging device, or biological unit divided by the
spectral irradiance
, simplified expression:
,
where
is the magnitude of the output signal for
irradiation at
wavelength 
and
is the
spectral irradiance of the parallel and perpendicular incident beam at the same
wavelength.
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2276
PAC, 1995, 67, 1745
(Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995))
on page 1749
