The primary function of light reactions in photosynthesis is to capture light energy and convert it into chemical energy in the form of ATP and NADPH.

Here's a breakdown:

* Light Absorption: Chlorophyll and other pigments in photosystems absorb light energy.

* Electron Excitation: This energy excites electrons within the pigment molecules, causing them to jump to a higher energy level.

* Electron Transport Chain: These excited electrons are passed along a series of electron carriers, releasing energy as they move.

* ATP Production: Some of this energy is used to generate ATP (adenosine triphosphate), which is the primary energy currency of cells.

* NADPH Production: The energy from the excited electrons is also used to reduce NADP+ to NADPH, a reducing agent carrying high-energy electrons.

Essentially, the light reactions act like a solar panel, converting light energy into a usable form of chemical energy that can be utilized in the subsequent dark reactions (Calvin cycle) to produce sugars.