Under what circumstances does oxygenic photophosphorylation use non-cyclic photo

Oxygenic photosynthesis generates ATP via ATPase from a proton motive force, created by electron transport. Electrons are used to reduce NADP+ and form NADPH (reducing power); thus electrons are not cycled. When sufficient quantities of NADPH are made, electrons are used to cycle through the electron transport chain, and P680 (PSII) is re-reduced. During cyclic photophosphorylation, electrons are transferred in a closed system where there is no consumption or input of electrons. NADPH is not made, instead additional ATP is synthesized from the added proton motive force generated.