spectral responsivity

The spectral output quantity of a system such as a photomultiplier, diode array, photoimaging device, or biological unit divided by the spectral irradiance $s λ = d y λ d E λ$ , simplified expression: $s λ = Y λ E λ$ , where $Y λ$ is the magnitude of the output signal for irradiation at wavelength $λ$ and $E λ$ is the spectral irradiance of the parallel and perpendicular incident beam at the same wavelength.