What are the two important changes during light reaction?

The light reactions occur primarily in the thylakoid membrane of the chloroplast. They take the energy of light and use it to make the high energy molecules NADPH and ATP.

Chlorophyll absorbs light, which then causes it to lose an electron. The electron is taken by the primary electron acceptor, which distributes it into a complex of proteins that pass it from molecule to molecule like a game of hot-potato. This is called the electron transport chain.
As the molecules pass the electron they pump hydrogen ions from one side of the membrane to the other. The high concentration of hydrogen ions pumped into the inner thylakoid space (the thylakoid lumen) can then be used to make ATP by a process called chemiosmosis. The electron finally gets dumped on the molecule NADP (Nicotinamide adenine dinucleotide phosphate) changing that molecule into NADPH.
The chlorophyll molecule left without an electron can take that electron from water splitting the water into Hydrogen ions and oxygen gas. This is why photosynthesis releases oxygen into the air.

The point of the Light reactions is to make large quantities of NADPH and ATP. These molecules store chemical energy that is used to power the dark reactions. The cell needs this energy because making sugar is hard work.
these answers will help you


1.In the light stage - sunlight is used to produce ATP and NADPH2. 
2.In the dark stage - the ATP & NADPH2 are used to fix CO2 into glucose.
1. ADP is phosphorylated to ATP
2. CF0 and CF1 are produced