In order to understand how J90 depends on the key photophysical parameters of the emitter, we have plotted the graphs shown in Fig. . Fig. shows J90 as a function of the radiative rate constant, 𝑘 ! " . There is little correlation between J90 and 𝑘 ! " (Spearman correlation of ρ = -0.228), and the highest values of J90 (around 10 mA cm -2 ) are achieved over a wide range of rate constants (4 -100 × 10 6 s -1 ). Fig. shows how J90 depends on kRISC. There is some correlation (ρ = 0.638) in so far as there is a tendency towards higher J90 for higher kRISC, but there is an enormous spread of the data (considering this is a log-log plot). For example, the blue dashed rectangle shows that J90 of approximately 2 mA cm -2 can be achieved with kRISC from 2 -20 × 10 DEST. Remarkably, even though this is one of the key design parameters for TADF materials, there is a weak correlation (ρ = -0.435), with a large spread. As one factor affecting the relative populations of singlets and triplets is the relative values of kRISC and kISC, we have also plotted kRISC/kISC as a function of DEST (Fig. ). As DEST is reduced from 0.2 eV to 0.1 eV, kRISC/kISC increases by more than two orders of magnitude.