Six Basic Knowledge Points of Plant Lighting
Definition of LED Plant Lighting
LED can emit narrow-spectrum monochromatic light within the range of 300-800nm for plant physiological effective radiation. The light quality is rich, the light spectrum of the light source can be combined and modulated, and the light environment can be intelligently controlled. LED light sources have the advantages of being environmentally friendly, energy-saving, small in size, cold light source, low voltage, and direct current. They are hailed by industry experts as the ideal light source for facility agriculture.
LED plant lighting falls under the category of agricultural semiconductor lighting. It can be understood as follows: It utilizes semiconductor electric light sources and their intelligent control equipment to meet the light environment requirements of plant growth and the production goals. By using artificial light to create an appropriate light environment or compensating for the lack of natural light, it regulates the growth of plants and achieves the production goals of "high quality, high yield, stable yield, high efficiency, ecological, and safe". This is an agricultural engineering measure.
LED plant lighting represents the innovative application of LEDs in the field of agriculture. Currently, the state is in the midst of compiling the "Terminology and Definitions for LED Lighting Used in Plant Growth".
LED Plant Lighting Applications
LED lighting can be widely applied in various fields such as plant tissue culture, leafy vegetable production, greenhouse supplementary lighting, plant factories, seedling factories, medicinal plant cultivation, edible fungus factories, algae cultivation, plant protection, space fruits and vegetables, flower planting, mosquito control, etc. The plants grown through this method, including fruits, vegetables, flowers, and medicinal herbs, can meet the needs of military border outposts, high-altitude areas, regions with scarce water and electricity resources, home office gardening, marine and space personnel, and special patients and other regions or groups.
At present, many LED plant lighting devices have been developed and produced in the market, such as LED plant growth lamps, plant growth boxes, home-use LED plant growth desk lamps, mosquito repellent lamps, etc. Among them, the common forms of LED plant growth lamps include bulbs, strips, panel lamps, light bands, tube lamps, and grids.
At present, there are over 150 enterprises engaged in LED plant lighting in China, mainly located in the Yangtze River Delta and the Pearl River Delta regions.
According to the prediction of the Chinese Academy of Agricultural Sciences, the agricultural semiconductor lighting market, including LED plant lighting, has a very broad prospect. Based on the current scale of China's agricultural industry, it is estimated that the demand for agricultural LED lighting fixtures and their control equipment will reach several billion yuan in the next five years, and will reach a hundred billion scale within 10 years, with an annual growth rate of 20% to 50%. The total scale of the agricultural semiconductor lighting industry will be over 100 billion yuan. It is particularly pointed out that plant seedling cultivation, plant tissue culture seedling production, edible fungus production, and livestock and poultry breeding will become leading fields. Replacing traditional light sources with LED light sources, plant factories and greenhouse supplementary lighting are the fastest-growing semiconductor lighting fields, with high technical content and strong intelligence and automation of equipment. They are the key areas for the development of the agricultural semiconductor lighting industry.
The LED plant lighting technology in China started relatively late. The application of LED light sources in plant factories will gradually become more widespread. There are still many obstacles in the industrialization of photobiological laws and LED light source devices and intelligent lighting control systems. Further research is still needed. According to the prediction of the Chinese Academy of Agricultural Sciences, China will become a major and powerful country in the world's agricultural semiconductor lighting technology equipment industry and its applications in the next 10 to 20 years.
Here are the 6 fundamental points you should know when entering the LED plant lighting industry.
Ⅰ. The demand for LED plant lighting is so huge. What are the major challenges if one wants to enter this market?
LED plant lighting is the result of the cross-disciplinary and organic integration of multiple fields such as biology, facility horticulture, vegetable science, plant physiology, plant nutrition, bio-environmental engineering, LED lighting, and intelligent control technology. Therefore, those who are only proficient in semiconductors, plants, or intelligent systems alone or in two of them are insufficient. Adequate collaboration and cross-research applications are of crucial importance. The biggest difficulty in entering the LED plant lighting market lies in developing and producing high-yield, high-quality, and ecological LED plant light sources or lamps. This requires simultaneously solving the problems of how to integrate and unite the intelligent regulation of the light environment, plant photobiology, and LED semiconductor technology.
II. What does plant photobiology refer to?
Studying the laws of plant photobiology is an important foundation for LED plant lighting. This includes researching the quantitative attributes of the light environment (light intensity and light cycle), the quality attributes (light quality and spectrum), and the emission characteristics of electric light sources (duty cycle, frequency), etc. Plant photobiology is highly complex and systematic. Light quality refers to the types of light that have an effect on organisms, including visible light, UV, and far-red light. In the field of light quality biology, we need to clarify the following issues: First, the biological functions of light quality, studying the physiological metabolism, molecular biology, and proteomics mechanisms of the effects of single light quality and composite light quality on plant growth and yield quality; second, the mechanisms of light quality adaptation and utilization differences among plant species and varieties; third, the biological mechanisms of the interaction between light quality and other environmental factors; fourth, the effective threshold and benchmark values of the quantitative attributes of light quality of lighting facilities. Additionally, the clear response mechanisms of the photoprocesses in plants under adverse light conditions, such as low light, strong light, and continuous illumination, also require research.
III. Why do different enterprises have different lighting formulas for the same plant?
Establish the basis for developing the LED plant lighting industry by formulating various light formulas necessary for plant growth and high-quality, high-yield production. The light formula is aimed at achieving high quality and high yield, and is a parameter set that includes the types and quantities of light qualities required by different plant species and varieties during their growth and development stages. The light formula suitable for each plant and different growth stages is different. Why do different enterprises have different light formulas for the same plant, even with significant differences? This is mainly related to the enterprises' goals for plant growth. To put it simply, enterprises can lower their requirements based on market demand and their own development needs. They only need to meet the minimum light formula requirements for plant growth and relax the requirements for other environmental conditions for biological growth. This will not only result in different light formulas but also different environmental control systems. On the contrary, enterprises can also be strict in their requirements and try to create the best growth environment and conditions for plants. In this way, the developed light formula will be good. In the future, as relevant standards and requirements in the LED plant lighting field of our country are successively introduced, the light formulas will gradually be unified or maintain consistency in basic conditions.
IV. What principles should be followed when developing and manufacturing LED plant growth lighting sources and lamps?
LED plant growth lighting sources and lamps are the core of the LED plant lighting industry. Enterprises need to develop the lighting sources and lamps required for plant growth based on the lighting formula. The following four principles should be noted: First, the principle of high light energy utilization rate. Design a reasonable spectral composition to maximize the luminous efficiency of the LED light source, reduce the distance between the light source and the illuminated plants, reduce light loss, and improve the utilization efficiency of light energy; Second, the principle of low cost. Cost is one of the most important factors determining the industrialization development of LED plant lighting; Third, the principle of ecological safety. In the red and blue spectra, increase the trace or small amount of green light components to enhance visual health; Fourth, prioritize the development of high-value-added LED light sources and lamps specifically for plants.
V. What is the control of plant light environment and what aspects does it cover?
Light environment control aims for high-quality and high-yield production, based on the lighting formulas for the growth stages of the plant species and varieties cultivated in each production system of the plant factory. It involves direct computer control and switching of light environment parameters for the management of time and space. For example, supplementary lighting in greenhouses needs to consider natural light diurnal variation parameters, environmental parameters, photosynthetic physiological parameters of plants, plant growth stages, and lamp attributes, and implement an economically effective supplementary lighting method to meet the requirements of light intensity, light quality, and light period, achieving energy-saving and efficiency. Plant light environment control mainly refers to controlling the light quality, light intensity, light period, spatial position, and moving speed of LED lamps. The light environment control has obvious temporal and spatial characteristics, so it is very important to establish dynamic real-time control. The automation and intelligence of LED plant lighting light environment control is the inevitable trend.
VI. What are the main indicators and performance aspects that are primarily focused on in the design of LED plant lighting fixtures?
The designer of LED plant lighting fixtures needs to pay attention to the following indicators and performances: 1. The uniformity of light; 2. The rationality of light quality combination; 3. The reliability of heat dissipation; 4. The suitability of LED chip power; 5. The efficiency of the light-emitting surface; 6. The visual comfort.
The influence of light quality on photosynthesis and light morphogenesis in plant lighting
The significance of light for plants
Light is one of the most important environmental factors for plant growth and development. 43% to 52.5% of the solar light reaching the ground has wavelengths ranging from 400 to 700 nm, which is the visible light that the human eye can perceive. This is precisely the energy and environmental signals for photosynthesis, which influence the growth, development, yield and quality of plants through the photosynthetic and photomorphogenesis pathways.
First, photosynthesis is the foundation for the formation of plant biomass and yield. 95% of the dry matter in plants originates from the carbohydrates produced through photosynthesis. Plants have complex responses to light conditions, including photoreception, photoinhibition, photoadaptation, and shade avoidance responses. Only a portion of the wavelengths in the solar color spectrum are absorbed by plants to facilitate photosynthesis, and the leaf morphology of plants, as well as their physiological responses, all affect photosynthesis.
Second, photomorphogenesis refers to the process in which light acts as an environmental signal to regulate plant growth, differentiation, and development. The receptors that sense light are present in very small quantities in plant cells, but they are highly sensitive to changes in the external light environment. For instance, the red light range of 600-700nm promotes the germination of lettuce seeds, while the far-red light range of 720-740nm inhibits the germination of lettuce seeds.
What does "glutinous fat" refer to?
Plants utilize various wavelengths for photosynthesis. That is to say, plants have selectivity in their response to light. Approximately 60% of the light energy absorbed by plants falls within the visible light spectrum (380-760nm). The absorption peaks are mainly in the wavelength range of 610-720nm (with a peak at 660nm) for red-orange light and 400-510nm (with a peak at 450nm) for blue-violet light. These two bands are regarded as the "light fertilizer" for plants. LED can emit single-color light required for plant growth. When combined, these single-color lights can form the light spectrum necessary for plant photosynthesis and morphological development. LED plant growth light sources can increase the light energy utilization rate of plants.
What are light and institutions? How are they affected?
In the broad sense, photosynthetic organs refer to the structures that can carry out part or all of the photosynthesis process, ranging from small components like chloroplasts and thylakoids to larger entities such as mesophyll cells, leaf organs, and even the entire plant body. In the narrow sense, it specifically refers to chloroplasts.
First, the photosynthetic apparatus is affected by light stress. Excessive or insufficient light will cause light stress in plants, inhibiting photosynthesis and reducing photosynthetic efficiency. Weak light leads to chlorosis, while under strong light, plants produce reactive oxygen free radicals, resulting in photoinhibition.
Second, the photosynthetic apparatus is affected by temperature. Periodic changes in temperature influence the carbon fixation, reduction, sucrose synthesis, transportation and distribution of photosynthetic products, as well as electron transfer in plants.
Thirdly, the photosynthetic apparatus is affected by nutrient supply. Nitrogen nutrition is the foundation of a plant's life. The correlation coefficient between leaf photosynthetic capacity and nitrogen content is on average 0.9. The light saturation photosynthetic rate increases linearly with the increase in leaf nitrogen content.
Therefore, maintaining nitrogen nutrition and the supply of other elements related to chlorophyll synthesis metabolism is very important for ensuring the activity of the photosynthetic apparatus.
Fourth, the photosynthetic apparatus is affected by carbon dioxide. Carbon dioxide is the main raw material for photosynthesis. An increase in the concentration of carbon dioxide in the air below the saturation point can enhance the photosynthetic rate of plants, reduce transpiration, inhibit plant respiration, and significantly improve the water utilization efficiency of plants. Maintaining an appropriate concentration of carbon dioxide is crucial for promoting carbon dioxide.
Fifth, the photosynthetic apparatus is affected by factors such as humidity and wind speed. Excessively high or low stomatal conductance, as well as excessive air relative humidity, will reduce the stomatal conductance of plant leaves, increase the resistance of carbon dioxide entering the leaves, and lower the transpiration rate. Especially under conditions of low water and fertilizer supply, it is prone to cause insufficient water and nutrient supply for the plants, thereby reducing the effect of increasing carbon dioxide supply. The size of wind speed will affect the uniform distribution of carbon dioxide within the plant canopy and the community, and also affect the effect of increasing carbon dioxide supply. Under conditions of adequate water supply, high concentrations of carbon dioxide increase the stomatal conductance of soybean leaves and reduce water evaporation.
What are the effects of the main light emitted by LEDs on plants?
Red light
In the visible light spectrum, the wavelengths that are absorbed the most by green plants are red-orange light (with a wavelength of 600-700nm) and blue-violet light (with a wavelength of 400-500nm), while green light (with a wavelength of 500-600nm) is only absorbed in trace amounts. Red light was the earliest light quality used in crop cultivation experiments and is a necessary light quality for the normal growth of crops. Its biological demand quantity ranks first among all single-color light qualities and is the most important light quality among artificial light sources. The substances produced under red light make plants grow taller, while the substances produced under blue light promote the accumulation of proteins and non-carbohydrates, increasing the weight of the plants. Supplementary far-infrared radiation reduces the concentrations of anthocyanins, carotenoids, and chlorophyll by 40%, 11%, and 14% respectively, and increases the fresh weight, dry weight, stem length, leaf length, and leaf width of the plants by 28%, 15%, 14%, 44%, and 15% respectively. Red light regulates photomorphogenesis through photoreceptors; red light drives photosynthesis through photosynthetic pigments; red light promotes stem elongation, promotes carbohydrate synthesis, and is conducive to the synthesis of VC and sugar in fruits and vegetables; but inhibits nitrogen assimilation. However, it is still somewhat difficult to cultivate plants well with only red light.
Blue light
Blue light is an essential supplementary light quality for crop cultivation and is necessary for the normal growth of crops. Its intensity is second only to red light in terms of biological usage. Blue light inhibits stem elongation and promotes chlorophyll synthesis, which is beneficial for nitrogen assimilation and protein synthesis, as well as the synthesis of antioxidant substances. Blue light affects the phototropic behavior, photomorphogenesis, stomatal opening, and photosynthesis of plants. The combination of LED red light and LED blue light can increase the dry matter content, seedling number, and seed yield of wheat, and increase the dry matter content of lettuce. Blue light significantly inhibits the growth of stem of loose-leaf lettuce. Increasing blue light in white light can shorten internodes, reduce leaf area, lower relative growth rate, and improve N/C efficiency. Higher plants synthesize chlorophyll and form chloroplasts, and have a high ratio of chlorophyll a/b and a low chloroplast. All of these require blue light. Excessive blue light is not conducive to plant growth and development. The combination of red and blue light has a greater effect on promoting the growth and development of vegetable seedlings than red light or blue light monochromatic light. The proportion of red and blue light combinations required by different plants is different.
Green light
Green light and red-blue light can be harmoniously adjusted to adapt to the growth and development of plants. Generally, under red-blue LED composite light, plants appear slightly purple-gray, making it difficult to diagnose diseases and imbalances. This can be solved by supplementing a small amount of green light. The effect of green light is usually opposite to that of red-blue light. For example, green light can reverse the opening of stomata promoted by blue light. Under strong white light, the quantum yield of photosynthesis in chloroplasts in the upper part near the light surface is lower than that in the lower part of the chloroplasts. Because green light penetrates the leaves more than red light and blue light, the lower chloroplasts absorb more additional green light than additional red light and blue light, which can increase the photosynthesis of the leaves to a greater extent. When cultivating plants under low light intensity, green light need not be considered. For plants in low-density and low-canopy-thickness facilities, green light need not be considered either. When the light intensity is high, the canopy thickness is high, and the density is high, green light must be considered.
Yellow light and orange light
Yellow light, orange light, green light and purple light are all important photosynthetically active radiation, but they are less demanded by plants. Adding yellow light to the basis of red and blue light can significantly enhance the growth of spinach seedlings. Yellow light has the best effect in improving the nutritional quality of leaf lettuce, but blue light is more conducive to significantly increasing the content of mineral elements in lettuce. Adding yellow light and purple light can enhance the photosynthetic ability of cherry tomato seedlings and alleviate the stress of weak red and blue light. Compared with white light, purple light and blue light increase the activity of antioxidant enzymes, delay the aging of plants, while red light, green light and yellow light inhibit the activity of antioxidant enzymes and accelerate the aging process of plants.
Far-red light
Although the far-red light with a wavelength of 730nm has little significance for photosynthesis, its intensity and the ratio between it and the 660nm red light play an important role in the formation of plant morphology, such as plant height and internode length. By adjusting the light quality and controlling the R/FR ratio, the plant morphology and plant height can be regulated. When the ratio increases, the distance between plant stem nodes becomes smaller, the plant becomes shorter, and the reproductive plants tend to elongate. Changes in the ratio also have varying degrees of influence on axillary bud differentiation, chlorophyll content, stomatal index, and leaf area. The selective absorption of red light by plants and the selective transmission of far-red light enable plants located in shaded areas to be in a light environment rich in far-infrared rays.
Ultraviolet light (UV)
The wavelength range less than 380nm is called ultraviolet light. According to the physical and biological properties of ultraviolet rays, the wavelength range of 320~380nm is long-wave ultraviolet (UV-A), the wavelength range of 280~320nm is medium-wave ultraviolet (UV-B), and the wavelength range of 100~280nm is short-wave ultraviolet (UV-C). 95% of the UV rays reaching the ground are UV-A. In the solar light spectrum, photosynthetically active radiation, UV, and far-red light have regulatory functions on plant growth and development. Ultraviolet radiation reduces plant leaf area, inhibits the elongation of the hypocotyl, lowers photosynthesis and productivity, makes plants more susceptible to pathogens, but can induce flavonoid synthesis and defense mechanisms. In an environment with low UV-B radiation, plants grow excessively, and it also hinders the synthesis of plant pigments, making it difficult to be used for covering vegetables like tomatoes and peppers. One important feature of a plant factory is the lack of UV-A and UV-B radiation in the sunlight. Complete absence of UV radiation will bring negative effects on production and affect plant growth and development. Therefore, it is very necessary to regulate the radiation level of UV in the plant factory, and it is necessary to pay attention to based on the production requirements and the response patterns of plants' tolerance.
Source: Sohu.com
