What is the difference between our LED grow lights and sunlight?
Sunlight contains roughly equal amounts of red, green, blue, and far-red light. At Signify, our LED lighting solutions provide a combination of colors optimized for plant growth and energy efficiency. One of the advantages of LED lighting is that this spectrum can be tailored. Different crops require different spectra, but most of our light spectra have relatively little green light. There are several myths surrounding the use of both white light and green light – such as that the latter penetrates deeper into the canopy and therefore leads to better growth.
Why do people think that green light penetrates deeper into the canopy?
Plants are green, which means that green light is partially reflected by the leaves of the plants. Therefore, it does seem very plausible that green light penetrates deeper into the canopy. To investigate this, we did several measurements in crop canopies and found some surprising results.
Up till now, many researchers have measured the optical properties of single leaves. As we know, light is either absorbed, reflected, or transmitted by leaves. From these measurements in a single leaf, they have found that the absorption of green light is about 80% whereas that of blue and red light is higher, about 90%. Also, about 10% of the green light is transmitted by the leaf, compared to only a few percent of the red and blue light. The absorption of far red light is much lower as well. From this, it seems plausible that green light penetrates deeper than red and blue light.
However, it is risky to draw conclusions from measuring a single leaf, since light transmission in a larger canopy of leaves is much more complicated. To see how the spectrum and intensity changes through a canopy, we decided to take a practical approach and measure the spectrum at different heights in real plant canopies as they occur in commercial greenhouse conditions.
Does that mean that green light behaves differently in a real plant canopy?
Let us start by looking at graph 1. Here, we measured the light at three different heights in a rose canopy (measured in a greenhouse at the Improvement Center Delphy, 2018). First of all, the blue line shows you the amount of light and the spectral distribution measured just above the crop (which is the sunlight spectrum). After that, we measured at a height halfway in the canopy (the red line) and finally we measured at the bottom of the canopy, at the height where you would cut the crop (the grey line).