# Light saturation point

> The light saturation point is the PPFD above which photosynthesis stops rising; for cannabis it is unusually high and moves upwards with CO2 and temperature.

- Canonical: https://genetixbay.com/knowledge/glossary/light-saturation-point.html
- Also written: saturation point, LSP, light saturation, photosynthetic saturation
- Glossary category: Environment and light · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

The light saturation point is the light level at which a leaf's [photosynthetic](https://genetixbay.com/knowledge/glossary/photosynthesis.md) rate plateaus: more photons no longer raise carbon gain. It is read from a light-response curve. It is not a fixed number. It rises with [CO2](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) concentration and with temperature up to the optimum, and it differs between single leaves and whole canopies, where lower leaves are shaded.

## In practice

Chandra and colleagues (2008) measured cannabis leaf photosynthesis rising to around 1,500 [µmol/m²/s](https://genetixbay.com/knowledge/glossary/ppfd.md) at 25–30 °C (77–86 °F) and ambient CO2. Whole-plant trials go further: Rodriguez-Morrison and colleagues (2021) saw flower yield keep rising up to about 1,800 µmol/m²/s, because a canopy saturates later than any one leaf. *Established*.

For growers, the useful idea is diminishing returns. Each extra 100 µmol/m²/s above about 1,000 buys less, costs the same in power and heat, and needs more CO2 and tighter [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) to pay off. Many rooms without CO2 enrichment stop at 900–1,100 µmol/m²/s for that reason.

## Don't confuse with

- **Light compensation point**: the low end, where photosynthesis just balances respiration.
- **Light stress**: damage when absorbed light exceeds what the leaf can use or dissipate; it can happen below the saturation point if heat or VPD is wrong.

## Related terms

[PPFD](https://genetixbay.com/knowledge/glossary/ppfd.md), [Light compensation point](https://genetixbay.com/knowledge/glossary/light-compensation-point.md), [CO2 enrichment](https://genetixbay.com/knowledge/glossary/co2-enrichment.md), [Light stress](https://genetixbay.com/knowledge/glossary/light-stress.md)

## Read more

- [PPFD and DLI by stage, with the evidence](https://genetixbay.com/knowledge/environment/ppfd-dli-by-stage.md)
- [CO₂ enrichment: when it pays, how much, and how to stay safe](https://genetixbay.com/knowledge/environment/co2-enrichment.md)

## Sources

1. Chandra S, Lata H, Khan IA, ElSohly MA, 2008. Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions. Physiology and Molecular Biology of Plants 14(4):299–306. https://doi.org/10.1007/s12298-008-0027-x
2. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020