How Much Light Can Cannabis Plants Use?
It is common to hear that “more light is better” and since many home growers use insufficient lighting for their space, it is often true. However, there is a limit to the density of photons (PPFD) that cannabis plants can use. If plants are exposed to a higher density of photons than they can use in photosynthesis, it will not increase yield. In fact, when PPFD is too high, it can reduce both the yield and the quality of the harvested cannabis.
The rate of photosynthesis and photosynthetic efficiency can be limited by several factors including carbon dioxide, photon density, temperature, oxygen, water, minerals, age, leaf anatomy and more. In many grow tents, photon density is the limiting factor. However, as you increase the density of photons, other factors like carbon dioxide will become the limiting factor. When photosynthesis is limited by any factor other than light, the leaves reach their light saturation point.
Photon density (PPFD) that is beyond the saturation point dictated by photosynthesis can damage plant tissue. Therefore, when leaves reach their saturation point, the plant will attempt to protect itself with photoprotection responses. These include things such as chlorophyll or leaf movement, anatomical changes, non-photochemical quenching and thermal dissipation. All these photoprotection efforts by the plant waste energy and can lower yield.
If the plant cannot adequately protect itself from excessive light energy by using photoprotection responses, it will begin photoinhibition. Photoinhibition decreases the rate of photosynthesis and reduces growth and harvest potential. However, symptoms of light stress do not become apparent if the plant is able to cope with the excessive light. Symptoms such as chlorosis occur only when photoinhibition can no longer effectively protect the plant.
