spectral (photon) effectiveness

The reciprocal of the photon fluence rate, E p 0, at wavelength λ, causing identical photoresponse, Δ y, per unit time (Δ y Δ t). The effectiveness spectrum is directly proportional to the conversion spectrum of the sensory pigment, if spectral attenuance is negligible.
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2275 (https://doi.org/10.1351/pac199668122223)