Water and light.
The light dependent reaction uses water and light.
Light provides the energy needed to break apart water molecule. This process will make oxygen and hydrogen ions. The hydrogen ions are used to make ATP.
This video shows lab video of an experiment and provides a brief summary of the process of . You can see plants releasing bubbles of oxygen produced during the light reaction.
This second video provides a more in-depth review of the process of photosynthesis.
Hope this helps!