The protein complex that absorbs light energy and uses it to produce NADPH is Photosystem I (PSI).

Here's how it works:

1. Light Absorption: PSI absorbs light energy using its chlorophyll molecules.

2. Electron Excitation: The absorbed light energy excites electrons within PSI.

3. Electron Transfer: The excited electrons are passed down an electron transport chain within PSI.

4. NADPH Production: At the end of the chain, the electrons reduce NADP+ to NADPH. This is the primary way that NADPH is produced during photosynthesis.

Key points:

* Photosystem II (PSII) is another important photosystem involved in photosynthesis, but it primarily produces ATP (adenosine triphosphate), not NADPH.

* The process of producing NADPH by PSI is crucial for the Calvin Cycle, the stage of photosynthesis where carbon dioxide is converted into glucose.

Let me know if you have any other questions!