Views:23 Author:Site Editor Publish Time: 2018-03-25 Origin:Site
In the last two or three years, there have been numerous reports on the application of semiconductor lighting technology in stereoscopic plant factories or plant growth. But when you read it down, there is always a feeling of anxiety. In general, there is no real understanding of what role light application should play in plant growth. Grow light.
Illumination plays a key role in plant growth. It is the best fertilizer for promoting the absorption of plant chlorophyll and the absorption of various plant growth materials such as carrots. However, the decisive factor in determining the growth of plants is a comprehensive factor, not only related to light, but also inseparable with the allocation of water and soil fertilizers, environmental conditions for growth and comprehensive technical control.
In the last two or three years, there have been numerous reports on the application of semiconductor lighting technology in stereoscopic plant factories or plant growth. But when you read it down, there is always a feeling of anxiety. In general, there is no real understanding of what role light application should play in plant growth. china led
First of all, to understand the sun's spectrum, as shown in Figure 1. It can be seen that the solar spectrum is a continuum where the blue and green spectrums are stronger than the red spectrums, and the visible spectrum ranges from about 380 to 780 nm. The growth of natural organisms is related to the intensity of the spectrum. For example, in the vicinity of the equator, most plants grow at a very fast rate and grow at a relatively large size. However, the intensity of the sun's irradiation is not as high as possible, and it is selective for the growth of plants and animals. china grow light
Figure 1 Characteristics of the solar spectrum and its visible light spectrum
Secondly, the second spectrum diagram of several key absorption elements for plant growth is shown in Figure 2.
Fig. 2 Absorption spectra of several auxins in plant growth
As can be seen from Figure 2, several key auxins that affect plant growth are significantly different from the light absorption spectra. Therefore, the application of LED plant growth lights is not a simple matter, but very targeted. It is necessary here to introduce the concept of the two most important photosynthetic plant growth elements.
Chlorophylls are the most important pigments associated with photosynthesis and are found in all organisms that contribute to photosynthesis, including green plants, prokaryotic blue-green algae (blue fungus) and eukaryotic algae. Chlorophyll absorbs energy from light, and energy is then used to convert carbon dioxide into carbohydrates.
Chlorophyll a mainly absorbs red light, and chlorophyll b mainly absorbs blue-violet light, mainly for distinguishing shade plants from positive plants. The ratio of chlorophyll b and chlorophyll a in the shade plants is small, so the shade plants can use blue light strongly to adapt to the shade. Chlorophyll a is blue-green, and chlorophyll b is yellow-green. There are two strong absorptions of chlorophyll a and chlorophyll b, one in the red region with a wavelength of 630-680 nm, and the other in the blue-violet region with a wavelength of 400-460 nm.
Carotenoids are a group of important natural pigments that are commonly found in yellow, orange-red or red pigments of animals, higher plants, fungi, and algae. More than 600 natural carotenoids have been discovered so far.
Carotenoids absorb light in the range of OD303-505 nm, which provides the color of food and affects the body's intake of food; in algae, plants, and microorganisms, they cannot be represented because their color is covered by chlorophyll. In plant cells, the carotenoids produced in addition to the absorption and transfer of energy help the photosynthesis process, but also have the function of protecting the cells from the excited single-electron bond oxygen molecules.
Misconceptions in some concepts
Regardless of the energy saving effect, the selectivity of light and the cooperation of light, semiconductor lighting has shown great advantages. However, from the rapid development of the past two years, we have also seen a lot of misunderstandings in the design and application of light, which are mainly reflected in the following aspects. shenzhen led grow light
1 As long as the certain wavelength of red and blue chips are combined in a certain proportion, they can be applied to the cultivation of plants, for example, the ratio of red to blue is 4:1, 6:1, 9:1 and so on.
2 As long as it is a white light, it can replace the sun's light, such as the three-color white light tube widely used in Japan, etc. The use of these spectra has a certain effect on the growth of plants, but the effect is not as good as the light source made by LED.
3 As long as it is an important parameter of light PPFD (photon flux density) to achieve a certain target, for example, PPFD is greater than 200 μmol·m-2·s-1, but when using this indicator must pay attention to Plants are also living plants. To search or find the light compensation points of these plants, it is also called light compensation point. In practical applications, seedlings are often burned or withered. Therefore, the design of this parameter must be designed in accordance with the plant species, growth environment and conditions.
Regarding the first aspect, it has been explained in the introduction that the spectrum required for plant growth should be a continuum with a certain width of distribution, and the use of red and blue is very narrow in the spectrum (Figure 3(a)). The light source made by the wavelength chip is obviously not suitable. In the experiment, it was found that the plants will appear yellowish, the stems and stems are very light, and the leaf stems are very thin.
For fluorescent tubes that are commonly used in previous years and dominated by three primary colors, although they are synthesized in white, their red, green, and blue spectra are discrete (Figure 3(b)), and the width of the spectrum is very narrow. The spectral intensity of the following continuous part is relatively weak, while the power is still relatively large compared to the LED and so on, 1.5 to 3 times the energy consumption. Therefore, the use of effects is not as good as LED lights.
Figure 3 Red and blue chip LED plant light and trichromatic fluorescent light spectrum
PPFD is the photon flux density, which refers to the effective flux density of light in photosynthesis, and represents the total number of photons incident on the leaf stem of the plant in a wavelength range of 400 to 700 nm per unit time. Its unit is μE·m-2·s-1 (μmol·m-2·s-1). The photosynthetically active radiation (PAR) is the total solar radiation with a wavelength in the range of 400-700 nm. It can be represented either by light quanta or by radiant energy.
The intensity of light reflected by the previously used illuminometer is brightness, but the spectrum of plant growth is used as light when studying photosynthesis because the light source of the plant grows away from the height of the plant, the coverage of the light, and whether light passes through the leaves or the like. Strong indicators are not exact enough and most of them now use PAR.
Generally, PPFD> 50 μmol·m-2·s-1 for positive plants could initiate photosynthesis mechanism; PPFD for negative plants only required 20 μmol·m-2·s-1. Therefore, when purchasing LED plant lights, the number of LED plant lights can be selected based on this reference value and the type of plant they are planting. For example, if the single LED plant bulb PPFD is 20 μmol·m-2·s-1, more than three LED plant bulbs are required to grow a positive plant.
Several kinds of semiconductor lighting design
Semiconductor lighting is used for plant growth or planting. There are two basic reference methods.
At present, the domestically heated indoor planting model is very hot. This model has several features:
The function of the 1 LED lamp is to provide the full spectrum of the lighting of the plant, which requires the lamps to provide the full lighting energy, and the production cost is relatively high;
The design of 2LED plant growth lamps needs to consider the continuity and integrity of the spectrum;
3 The lighting time and lighting intensity need to be controlled effectively. For example, if the plants are allowed to rest for a few hours, the intensity of irradiation is not enough or too strong.
4 The whole process needs to imitate the conditions that plants need in the actual best growing environment outdoors, such as humidity, temperature, and CO2 concentration.
There is a good outdoor planting pattern for outdoor greenhouses. The characteristics of this mode are:
The role of the 1LED lamp is to fill light. First, to strengthen the light intensity in the blue and red light areas during the daytime to promote the photosynthesis of plants, and secondly, to compensate for the lack of sunlight during the night to promote the plant. Growth rate;
2 Fill light needs to consider which growth stage the plant is in, such as the nursery period or the fruiting period.
Therefore, LED plants encourage the design of lamps first, there should be two basic design patterns, namely, all-weather lighting use (indoor) and plant growth light use (outdoor). For indoor planting, the design of the LED plant to encourage the lamp needs to consider three aspects, as shown in Figure 4. It is not possible to directly take the chips of the three primary colors in a certain proportion.
Figure 4 Design ideas for using indoor LED plants to encourage lights for all-weather lighting
For example, a spectrum of the nursery stage, considering that it needs to strengthen the growth of roots and stems, strengthen the split bifurcation, the use of the light source is in the room, so the spectrum can be designed in the form of Figure 5.
Figure 5 Spectral structure suitable for indoor seeding stage of LED
For the design of the second type of LED plant booster lamp, the design plan for supplementing the light and propagating the base in the outdoor greenhouse is mainly aimed at. The design idea is shown in Figure 6.
Figure 6: Design ideas for outdoor plants to encourage lamps
The authors suggest that more growers adopt the second scheme to use LED lamps to promote plant growth.
First of all, China's outdoor greenhouses have been planted for decades, with large scales, large volumes in both the South and the North, and a good technology base for greenhouse cultivation, providing a large number of freshly-listed fruits and vegetables for neighboring cities, especially in the presence of soil and fertilizers. Planting has achieved rich research results.
Secondly, this supplemental light scheme can greatly reduce the unnecessary consumption of energy and at the same time it can effectively increase the yield of fruits and vegetables. Together with the vast geographical position in China, it is very convenient for promotion.
As a scientific research of LED plant lighting, it also provides a broader experimental base. Fig. 7 is a kind of LED booster lamp that is suitable for growing light in greenhouses and developed by the research team. The spectrum is shown in Fig.8.