Photosynthesis Rate Calculator
The rate of photosynthesis at a given light level from a light-response curve — with the light-saturation point, the compensation point, and the carbon a canopy fixes in a day.
Photosynthesis rises with light and then saturates: the rectangular hyperbola P = Pmax × I / (K + I), less respiration, captures it.
How the photosynthesis rate calculator works
Photosynthesis rises with light and then saturates: the rectangular hyperbola P = Pmax × I / (K + I), less respiration, captures it. At low light the leaf is light-limited; past the saturation point more light does nothing.
The compensation point — where photosynthesis just balances respiration — is the light level below which a leaf is a net cost. Shade leaves have a lower one; that is how understorey plants survive.
Formula: P_net = Pmax × I / (K + I) − R
Worked examples
| Inputs | Net photosynthesis (µmol CO₂/m²/s) | Note |
|---|---|---|
| Bright light on a crop leaf | 16.682 | near saturation |
| Deep shade | 0.773 | close to compensation |
| A shade leaf | 6.873 | a lower compensation point |
FAQFrequently asked questions
What is a light-response curve?
Photosynthesis rate against light intensity — rizing steeply at low light, then saturating. The hyperbola here is the simplest model of it.
What is the light compensation point?
The intensity where photosynthesis exactly offsets respiration. Below it the leaf is a net cost; shade leaves sit around 10 to 20 µmol/m²/s, sun leaves higher.
What is light saturation?
The intensity past which more light adds nothing — CO₂ supply or enzyme capacity limits instead. Full sun is about 2,000 µmol/m²/s; most C3 leaves saturate well below it.
What are the units?
Micromoles of CO₂ fixed per square meter of leaf per second. Twenty is a good crop leaf in bright light; C4 plants like maize reach forty.
How does this scale to a canopy?
Not linearly — lower leaves are shaded. The daily carbon figure weights by light interception, which is why doubling leaf area does not double the yield.
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- National Human Genome Research Institute — the US genomics research institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.