Figure 6 (A) Relationship [Eqn. (15)] between the probability of kill for all *k* cells vs. normalized cumulative singlet oxygen concentration ([^{1}O_{2}]_{rx}/[^{1}O_{2}]_{rx0}), where [^{1}O_{2}]_{rx0} is the cumulative singlet oxygen to produce 1/*e* cell kill [Eqn. (14)]. The number of cells *k* varies between 10^{6} and 10^{14}. (B) [^{1}O_{2}]_{rx,sh}/[^{1}O_{2}]_{rx0} vs. *k* based on *P*=0.5 [Eqn. (16)].