It is an obvious trend that more and more new glasshouse projects are choosing diffuse glass instead of float glass. By switching the glass, growers are enjoying improved yields. So, someone will be curious about the theory back this technique and this is the topic we will discuss today.
The horticultural golden rule
“1 percent more light ensures 1 percent more yield”. This is a common accepted rule known by horticultural growers. However, this rule is effective under certain conditions. And the condition is that there is no photoinhibition happens. Or, in another word, the leaf had not reached its light saturation point (LSP).
An LSP is a point where the photosynthesis rate does not increase anymore with the increase of incident light intensity. Normally, in a range, the photosynthesis rate always increasing with the increase of light intensity. Once the light intensity exceeds certain value, the photosynthesis will barely increase. (Figure 1)
So, when we discussing about the yield improvement, the light is always abundant. The main issue in this condition becomes improving the utility of the incoming light. A graph below helps to demonstrate the different results of light coming through float glass and diffuse glass. (Figure 2)
Comparing with the float glass, the diffuse glass creates less shadows, making more leaves functional in photosynthesis. However, some people may doubt that the 70%+30% light on two leaves will not as good as 100% light on one leaf. Is that true?
Let us make a hypothesis that the total incident light intensity is 1000. For plant A, since there is no scattered light, the total incident light intensity will be 1000+0. While, for plant B, the light intensity will be divided into 700+300. So, we can easily find the corresponding photosynthesis rate in the curve given in Figure 1. (Figure 3)
Apparently, B is much larger than A. And since it is a Convex curve, you will find out that this is the common trend.
The actual growing environment is more complicated than the model, but the rule keeps unchanged. With a higher photosynthesis rate, the yield is improved thanks to the scattered light. And the scattered light is created by the diffuse glass.
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