Electrons in the light dependent reactions enter a cyclic pathway when the ratio of NADPH to NADP+ is high. In other words, when there is more NADPH than NADP+ available, this causes electrons to cycle from the photosystems and cytochrome complex since the electrons do not have anywhere to go. This pathway does not cause the production of NADPH but still causes the production of ATP.
Source: tatoeba (13715790)