Light intensity and duration


#1

Is it better to have light intensity or duration of light or does it even matter as long as you hit DLI ?


#2

What a great question that we as indoor farmers are uniquely positioned to research.

  1. Define “Is it better” - do you mean better for the plant, or better for the farmer? It may be more efficient to run very high intensity lighting for 8 hours during non-peak hours rather than 24 hours low intensity.
  2. Based on the crop type, I think there is a “max net photosynthetic response” rate that can be reached. Beyond that, you start to have problems, this varies based on many factors in environment, but at some point a plant can only react so fast. I would think that this max would then define the minimum photoperiod necessary to reach DLI.
  3. Photoperiod by itself is important as plants can flower based on short or long days, so this will always have to be factored into the equation when dealing with flowering plants (I assume your question is related to strawberries). So if your definition of “better” is more plants flowering quicker, then depending on the variety perhaps a longer phototperiod is what you should go for.

Great talk by Chieri Kubota on this topic:


#3

Thanks
I was just wondering if their was advantage to having less intense light but longer time.
I’m running 20 DLI in 8hrs which the plants are growing good.
Just seeing if their is something better


#4

You’ve probably read this, but I think this is the most comprehensive resource on Strawberries: https://cals.arizona.edu/strawberry/Hydroponic_Strawberry_Information_Website/Env._Control.html

“DLI - Daily light integral. Light requirement for winter strawberry production is not well known despite the status of widely practiced commercially in Asian countries. However, photosynthetic characteristics measured for strawberries show two interesting aspects in our literature review. First, the photosynthetic saturation point (the light intensity) is reportedly 800-1200 micro-mol/m2/s PPF (photosynthetic photon flux) (Morgan, 2006). The second interesting aspect reported elsewhere is that strawberry plants show relatively steep diurnal decline of net photosynthetic rate (Inaba, 2007), possibly due to the negative feedback of photosynthesis, suggesting that morning hours are critical time for promoting photosynthesis. Minimum DLI (daily light integral in mol/m2/d) has not been known partly due to the non-linear relationship between plant growth and the cumulative PAR. Day length also affects the dormancy status (rosette-type morphology), largely affecting the light interception (therefore canopy photosynthesis) as well as vegetative growth rate. More studies are needed to find the optimum light environment (photoperiod and DLI) for strawberry plants.”

This offers detailed analysis for a few specific cultivars: