The protein complex that absorbs the energy used to produce NADPH is Photosystem I (PSI).

Here's how it works:

1. Light Absorption: PSI absorbs light energy, primarily in the far-red region of the spectrum. This energy excites an electron within a special chlorophyll molecule called P700.

2. Electron Transfer: The excited electron is passed down an electron transport chain within PSI, losing energy along the way.

3. NADPH Production: The energy released during electron transport is used to pump protons across the thylakoid membrane, creating a proton gradient. This gradient drives the synthesis of ATP, which is then used by the enzyme NADP reductase to reduce NADP+ to NADPH.

So, in summary, PSI uses light energy to power the electron transport chain, which ultimately leads to the production of NADPH, a crucial reducing agent in photosynthesis.