From Equation , a relation can be drawn between the energy gap and the rate constant (Figure ). It can be seen that two regimes can be defined. Firstly, Kasha's regime, where Kasha's rule is obeyed, and a range in which the Ermolaev-Sveshnikova rule (large energy gaps yield weak internal conversion) is obeyed. It should be noted that there is also an intermediary regime, where internal conversion directly competes with fluorescence.