As for the topic to be addressed, much is said about the importance of “light” and its management in protected crops. First of all, the term “light” does not portray the proper way to approach this agronomic variable, as it is a very subjective term.
Radiation is the correct term to be used to address this issue. To be more specific, we can subdivide radiation into global radiation and photosynthetically active radiation (that which the plant uses to grow and develop). It is nothing more than a sum of electromagnetic wavelengths that living beings (plants) use for their metabolism.
Anyway, the approach to this subject in this edition aims to provide guidance in practical and not theoretical terms. Therefore, when dealing with radiation, we think of an adequate range that aims to meet the growth of plants. In practical terms this statement means: when there is an excess of radiation the plants burn (by photoinhibition). When there is a deficiency of radiation, the plants fester (become fluted). In both cases, such responses represent loss of quality, productivity and susceptibility to attack by pests and diseases.
How do we identify the appropriate radiation ranges?
First, and in a very general way, a range of 60,000 to 80,000 lumens is the range that serves plants grown in hydroponics well. If fine adjustments are made, species such as arugula need values closer to 60,000 lumens. Lettuce, especially purple lettuce, needs lumens close to 80,000, or even higher than this.
Parameterizing, radiation values measured in the open and at noon (sun to pin), depending on the region, can reach 125,000 lumens.
How to measure, monitor and reduce this excess radiation?
A good news for all of us is that today there are several applications for cell phones that make this measure, one that I use a lot was developed by prof. Nilton Cometti, from the Federal Institute of Panaltina, which can be found in the Android version by the name Estufa Inteligente. I recommend you watch.
With this APP, the measurement and monitoring will allow them to refine the management of radiation (irradiance, which is characterized by the number of photons per area per time).
How can we reduce excess radiation?
For this we have the shading screen, which can be black or aluminized, with a recommendation for the second, and for that reason we recommend screens between 35 to 50% transmittance. Let’s do a simple exercise: If we have a local data that at 11: 00h in the morning the irradiance is at 120,000 lumens and we are producing arugula, by covering these plants with the 50% screen, we will reduce the irradiance to 60,000 lumens, an appropriate value to the growth of hydroponic rockets.
On the other hand, we have this same situation for lettuce, that is, 120,000 lumens, so, with the use of a 35% shading screen, this irradiance will be reduced to 78,000 lumens, an adequate range for the growth of hydroponic lettuces.
In summary, the handling of the screen must be based on the reading of the radiation with the use of a device or an application so that the decision making is as assertive as possible. On the other hand, the lack of radiation is also recurrent in many producers. In general, it is associated with the non-retraction of the screen in the presence of clouds, as well as the excess of debris in the plastics (dirty or old plastic).