Referred to @[email protected] based on spectrophotometric measurements, \(S_{\text{ac}}\left(\lambda \right)=\varPhi \left(\lambda \right)\ \varepsilon\left(\lambda _{\text{obs}}\right)=\text{sensitivity or actinometric factor}\). \(\varPhi \left(\lambda \right)\) is the @[email protected] of the @[email protected] at the excitation @[email protected] and \(\lambda _{\text{obs}}\) is the observation @[email protected], which may be the same as or differ from the former.