We will begin with a qualitative argument, and then make it quantitative. In organic TADF emitters, there is a dynamic equilibrium between S1 and T1 via the cycling between ISC and RISC. We want to shift this dynamic equilibrium towards the singlet state to reduce the triplet population. To achieve this, two things are important. One is the relative magnitude of kRISC and kISC as higher kRISC/kISC increases the singlet population relative to the triplet population. The other is the relative magnitude of 𝑘 ! " and kISC. This is because when a singlet has been formed, the desired process of its radiative decay is in competition with intersystem crossing to the triplet. These considerations lead us to propose a figure of merit (FOM) for efficiency roll-off: