A fresher look at previously discussed concepts might be useful in light of the new general equations of rates (Eq. 19.5 ) and concentrations (Eq. 19.10 ) established in Chap. 19 . The target is to evaluate if these equations can help in characterising further or allow to establish general equations for the quantum yield and the photonic yield at low and high initial concentrations, irrespective of the nature (monochromatic or polychromatic) of the light used.