In this issue, we will try to give information about the techniques of the applications related to plant cultivation lighting, which we have discussed in general in our previous issue. First, let’s start with the answer to the question of “what is light”. Light is the electromagnetic radiation that covers a certain part of the electromagnetic spectrum. It can also be described as a form of energy that carries particles called “photons”. However, when we talk of “light” we usually refer to the visible spectrum in the wavelength range of 400 – 700 nm visible to the human eye, or, in other words, between ultraviolet and infrared.
The needs of plants for light, as well as their sensitivity to the components of light, are different than those of other living being. For instance, while humans are mostly sensitive to green light, plants are mostly sensitive to a wide range of colors. Especially red and blue light are the colors, in which photosynthesis is performed most efficiently. This difference brings with it the necessity that there should be a difference in measuring the amount of light. Since the sensitivity of the human eye to blue and red light is relatively low, the light is usually measured in “lux” or “lumen” units, while for the plants it would be more accurate to use the PAR unit (µmole m-2 s-1). PAR stands for “Photosynthetically Active Radiation”, i.e. the active radiation for living being capable of photosynthesis, and indicates the amount of the number of photons carried by light in the wavelength range from 400 to 700 nm.
Plants absorb light with the help of pigments such as chlorophyll, which they carry on their leaves, and convert it into glucose, i.e. nutrients and oxygen, through photosynthesis. We, on the other hand, release carbon dioxide, water and energy by burning this nutrient produced by plants with oxygen in our cells.
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Although we have known about the functioning of this “cycle” for many years, the subject of how the sunlight is most effectively evaluated by different plants is an area that continues to be investigated, for the purposes of plant cultivation lighting. Which plant responds best to the desired result during which growth period, at what time of day, on what spectrum, at what intensity and duration, and even from which direction when exposed to light, are the questions we are looking for answers. The answers to these questions form the “ideal light recipe” for that plant. For now, however, the information available to the public is mostly limited to the relationship between the color of light and the development of the plant. For example;
“The needs of plants for light, as well as their sensitivity to the components of light, are different than those of other living being.”
UV Light: Mainly, it activates the plant’s defense mechanism.
Blue Light :
● Prevents elongation,
● Triggers the opening of the stoma,
● Causes darker leaves and flowers,
● The absence of, or applying only blue color leads to excessive elongation.
Green Light : Destroys the effect of blue light,
Far Red: Increases blossoming and elongation.
Red/Far Red Ratio (R/FR):
● High R/FR ensures fast seedling growth,
● Low R/FR increases elongation,
● Intermittent application of low R/FR at night promotes blossoming. The point that should be remembered here is that sciophytes usually react differently.
In conclusion, it is clear that we are still at the “beginning of the road” in terms of determining the “light recipes” of plants. The public disclosure and further development of the know-how obtained from the existing applications is also very limited, as it is considered a trade secret. Therefore, for lighting manufacturers who want to work on or invest in this subject matter, preparing their own prescriptions with the experience they will gain in the field seems to be the only remedy for now.
