The concept of the effective Hamiltonian is introduced and the first- and second-order perturbative solutions are obtained for a nondegenerate system. By solving the first-order effective Schrodinger equation, the author derives the AC Poynting splitting for the exact field. In the long wavelength approximation, the AC Poynting splitting is shown to reduce to the AC Stark splitting if the electric dipole dominates and to the AC Zeeman splitting if the magnetic dipole dominates. For the quantised electromagnetic fields, it is found that the effective Hamiltonian approach does not distinguish between the conventional quantisation of the vector potential and the quantisation of the fields directly.