In which direction are hydrogen atoms moved as electrons travel between photosystem II and photosystem I?

1. As electrons move through the proteins between the two photosystems, they lose energy. 2. That energy is used to move hydrogen atoms from the stromal side of the membrane to the thylakoid lumen. 3. Those hydrogen atoms, plus the ones produced by splitting water, accumulate in the lumen. 4. The accumulation there is what will later be used to synthesise adenosine triphosphate. 5. Reversing the direction would empty the lumen rather than filling it, undoing the gradient. 6. The net result of all this is a low pH in the thylakoid lumen and a high pH in the stroma. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_