How much PAR can a plant take in at one time?


#1

Does anyone know how much PAR a plant can use at any given time?
I have heard 600 u/moles per sec i do not have anything to back that up.


#2

There is definitely a direct correlation to the airflow as well as Co2.

I would watch this talk regarding everything lighting by Cheri Kubota (who I’ll reference in third link and use her recommendations): https://www.youtube.com/watch?v=fPOt32WJyRM&list=PL7fPr3CuAdvv4ZPJKPvi4U7VblxKJnegD&index=2

Here is some good info by Cornell on lettuce, see the whole article here. Tipburn is a good example of a negative effect of an unbalanced growth recipe. What matters in this situation is the DLI, or total cumulative light for one growth day: http://www.ecaa.ntu.edu.tw/weifang/lab551/vegetable/culturalpractice/ten%20years%20of%20hydroponic%20lettuce%20research.pdf

If you want a specific answer to your situation, read this article which cites a 800-1200 umol photosynthetic saturation point for strawberries: https://cals.arizona.edu/strawberry/Hydroponic_Strawberry_Information_Website/Env._Control.html


#3

The light saturation point of plants depends on several factors. As Peter mentioned, Cornell’s lettuce production handbook provided a good example by designing their lettuce growing experiment with a DLI of 17 mols/day, and the graph shows increased dry mass with higher DLI. However, this can vary depending on the net photosynthetic rate of a plant, which are governed by the respiration, transpiration rate. The limiting factors come down to the CO2 concentration, root zone oxygen concentration, light quality, airflow (velocity matters), temperature and humidity. At certain point (before reaching plant’s genetic capacity) you will realize that it is always one factor that limits you from increasing the net photosynthetic rate.

With optimal design, the photosynthetic capacity increases and therefore leads to higher DLI value. In your case, if you are fixed with your PPF value (say 600), then you can extend the ON time of your light to achieve greater DLI, or simply providing higher PPFD by reducing the ON time. However, do mind that providing higher PPFD sometimes does not mean greater gain due to light saturation point that your plant can achieve in your system. Extensive experimentation needs to be conducted on your side. For plants with large canopy and thick leaf structure, I think 600 and up are okay. For smaller plants like leafy greens, I would suggest 600 max.