The spectral output quantity of a system such as a photomultiplier, diode array, @[email protected] device, or biological unit divided by the @[email protected] \(s(\lambda) = \frac{\text{d}y\left(\lambda \right)}{\text{d}E\left(\lambda \right)}\), simplified expression: \(s(\lambda) = \frac{Y_{\lambda }}{E_{\lambda }}\), where \(Y_{\lambda }\) is the magnitude of the output signal for @[email protected] at @[email protected] \(\lambda \) and \(E_{\lambda }\) is the @[email protected] of the parallel and perpendicular incident beam at the same @[email protected]