Photosynthesis Light Requirement Calculator

How it works

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂ · Photons ≈ CO₂ × quantum requirement (~8 per CO₂) · Photon energy per mole = N_A·h·c ÷ λ ≈ 0.1196 ÷ λ(m) J → kJ

Photosynthesis reduces CO₂ to sugar using light energy, releasing one O₂ per CO₂ fixed and building one glucose for every six CO₂. The light-dependent reactions need roughly 8–10 absorbed photons to fix each CO₂ — the quantum requirement — so the photon demand scales directly with carbon fixed. Multiplying photon count by the per-mole photon energy (which depends on wavelength) gives the minimum light energy input, a floor that real leaves exceed because not all light is absorbed or used.

Worked example

Fixing 6 mol of CO₂ at 8 photons each needs 48 mol of photons. At 680 nm each mole of photons carries about 176 kJ, so 48 × 176 ≈ 8450 kJ of light. That produces 6 ÷ 6 = 1 mol of glucose and releases 6 mol of O₂.

Sources: Photosynthesis — Wikipedia

Frequently asked questions