Photosynthesis is divided into 2 phases: light phase or light-dependent and dark phase or light-independent.
The light phase is so called because the energy of the photons of sunlight is captured in this phase. This energy is transferred to the electrons of the plant which are previously provided by water molecules.
When water gives up its electrons in the thylakoid, H+ is released for energy production, and O2 molecules are released through the stomata during the light phase.