Light Penetration Depth and the interplay with different Metrics and Why They Matter in GHs
At FOTONIQ, we work to optimize light conditions inside greenhouses using advanced coatings like PAR+. These coatings promote crop growth by diffusing incident light with less light loss than other diffusive coatings, but it’s just as important to understand how that light moves through the crop canopy - especially in tall or dense crops. That’s where the concept of light penetration depth becomes relevant.
What Is Light Penetration Depth?
Light penetration depth refers to how far light travels into a plant canopy before it gets significantly reduced. It’s typically defined as the depth at which the incoming light intensity has dropped with 37% of its original value at the top of the canopy.
This concept matters most in high-wire crops that have a vertical structure - like tomatoes, cucumbers, or peppers - where light reaching the lower leaves is essential for uniform growth, energy use, and yield.
Why This Matters
With PAR+, our goal isn’t just to increase the amount of light entering the greenhouse - but to help that light reach deeper into the crop where it can do the best. By focusing on vertical light distribution and understanding how light penetrates plant canopies, we give growers the tools to get more out of every photon.
Measuring Light Penetration Depth
There’s no single “right” tool to measure penetration depth, but there is a clear concept behind it. It’s a relative measure, independent of how much light enters the greenhouse through the roof. Instead, it depends on how light is affected by the crop.
Vertical Light Distribution / Attenuation Curve
The vertical light distribution measures how light intensity decreases with depth in the crop canopy. By placing sensors at different heights inside the greenhouse, we can build a light attenuation profile.
An attenuation profile is useful to show how uniform the received amount of light is at different heights of the canopy. Diffusing light redistributes some of the light excess from the top to lower levels of the canopy. This has two advantages:
1) The photosynthetic capacity of the lower leaves increases
2) The prevention of stress and inefficient light-use in the top of the canopy.
In direct light, the light excess at the top of the canopy can result in light stress and eventually in photoinhibition. Photoinhibition is a protective mechanism that decreases photosynthetic efficiency in response to light stress. In ornamental plants, severe photoinhibition can cause leaf discoloration and burn spots, reducing their aesthetic value. Diffusing light solves this problem.
Canopy Light Interception
While not a direct measure of penetration depth, canopy light interception tells us how much of the incoming light is reaching the crop. Higher light penetration usually means more light reaches deeper leaves, so there’s more total interception.
That said, interception and penetration depth aren't the same. Interception describes how much light is used, while penetration depth describes how deep it goes. Still, both metrics together can help growers understand the overall light use efficiency of their crop. If you would like to know how, get in contact with us.
Joris de Leeuw, Romy Steenkamer, Giacomo Bosco
