Photosynthesis makes use of the visible light band — wavelengths from ≈ 400 to 700 nanometer (nm) — of the electromagnetic spectrum. The “peak absorption” wavelengths are 400–450 nm and 650–700 nm. O[math]_2[/math] is “produced” in photosystem II, by fotolisi dell'acqua:

La reazione di scissione dell'acqua è catalizzata dal complesso di evoluzione dell'ossigeno del fotosistema II. Questo complesso inorganico legato alla proteina contiene quattro ioni manganese, più ioni calcio e cloruro come cofattori. Due molecole d'acqua sono complessate dal complesso di manganese, che poi subisce una serie di quattro rimozioni di elettroni (ossidazioni) per rifornire il centro di reazione del fotosistema II. Alla fine di questo ciclo, viene generato ossigeno libero (O[math]_2[/math]) e l'idrogeno delle molecole d'acqua è stato convertito in quattro protoni rilasciati nel lume del tilakoide. [ … ] the net oxidation reaction of water photolysis can be written as:

2 H[math]_2[/math]O + 2 NADP+ + 8 photons (light) → 2 NADPH + 2 H[math]^+[/math] + O[math]_2[/math].

[ … ] approximately one-third of the available light energy is captured as NADPH during photolysis and electron transfer. [ … ] Oxygen as a byproduct is of no further use to the reaction and thus released into the atmosphere.

Sunlight EM spectrum graph lifted from www.ces.fau.edu/NASA (Electromagnetic Radiation). Accompanying text (from the CSI website):

The Sun’s Electromagnetic Spectrum

The energy that reaches the Earth is known as solar radiation. Although the sun emits radiation at all wavelengths, approximately 44% falls within visible-light wavelengths. The region of the spectrum referred to as visible light (light our eyes can detect) is composed of relatively short wavelengths in the range 400 nanometers (nm), or 0.4 micrometers (μm), through 700 nm, or 0.7 μm.

Photosynthesis absorption spectrum lifted from Photosynthesis .ppsx (animated PowerPoint presentation).

The entire visible light spectrum, plus a bit.

Including most green light, contrary to what’s often said. Green is just the least efficiently absorbed by chlorophyll, and when considering a canopy, most of it is absorbed.

Light Absorption for Photosynthesis