Among the visible light, the red light is mostly absorbed by green plants, which is red orange light (wavelength 600-700nm) and blue violet light (wavelength 400-500nm), and only slightly absorbed by green light (wavelength 500-600nm). Red light is the first light quality used in crop cultivation experiments, which is necessary for normal growth of crops. The number of biological needs is the first of all kinds of monochromatic light quality, and the most important light quality in artificial light source. The substances produced under red light make the plant grow high, while the substances produced under blue light promote the accumulation of protein and non carbohydrate, and increase the weight of the plant. The concentration of anthocyanin, carotenoid and chlorophyll decreased by 40%, 11% and 14%, respectively, while the fresh weight, dry weight, stem length, leaf length and leaf width increased by 28%, 15%, 14%, 44%, and 15%, respectively. Red light regulates the formation of phototype through photopigment; red light drives photosynthesis through photosynthetic pigment absorption; red light promotes stem elongation and carbohydrate synthesis, which is conducive to the synthesis of VC and sugar in fruits and vegetables; however, it inhibits nitrogen assimilation. But it's a little difficult to grow plants well alone.
Blue light blue light is the necessary supplementary light quality of red light for crop cultivation, and it is also the necessary light quality for normal growth of crops. The biological dosage of light intensity is second only to red light. Blue light can inhibit stem elongation, promote chlorophyll synthesis, facilitate nitrogen assimilation and protein synthesis, and facilitate the synthesis of antioxidants. Blue light affects phototropism, photomorphogenesis, stomatal opening and Photosynthesis of leaves. Red LED light supplemented with blue LED light can improve the dry matter quality of wheat, the number of seeds and seed yield, and increase the dry matter quality of lettuce. Blue light significantly inhibited the growth of lettuce stem. Increasing blue light in white light can shorten internode, reduce leaf area, reduce relative growth rate and improve N / C efficiency. Blue light is needed for chlorophyll synthesis and chloroplast formation in higher plants, as well as for high chlorophyll a / B ratio and low chloroplast. Excessive blue light is not conducive to plant growth and development. Red and blue light combination spectrum can promote the growth and development of vegetable seedlings more than red light or blue light monochromatic light. The proportion of red and blue light combination required by different plants is different.
Green light, green light and red blue light can adjust the growth and development of plants harmoniously. Generally, under the red and blue LED compound light, the plant is slightly purple gray, which makes the disease and maladjustment symptoms difficult to diagnose, and can be solved by adding a small amount of green light. For example, green light can reverse the stomatal opening promoted by blue light. Under strong white light, the quantum yield of photosynthesis of chloroplast in the upper part is lower than that in the lower part. Because under strong white light, green light can penetrate the leaves more than red light and blue light, and the lower chloroplast can absorb additional green light to a greater extent than red light and blue light. Green light should not be considered for low light intensity plants, green light should not be considered for low density and low canopy thickness plants, and green light should be considered for high light intensity and high density and high canopy thickness plants. Yellow light, orange light, yellow light, orange light, green light and purple light are important photosynthetic effective radiation, but the demand of plants is small. Adding yellow light on the basis of red and blue light can significantly improve the growth of Spinach Seedlings. Yellow light is the best to improve the nutritional quality of leaf lettuce, but blue light is more conducive to significantly improve the content of mineral elements in lettuce. Adding yellow light and purple light can improve the photosynthetic capacity of cherry tomato seedlings and alleviate the red and blue light stress. Compared with white light, purple light and blue light increased the activity of antioxidant enzymes and delayed the senescence of plants, while red light, green light and yellow light inhibited the activity of antioxidant enzymes and accelerated the senescence process of plants.
Although the far red light at 730 nm has little significance for photosynthesis, its strength and its ratio to 660 nm red light play an important role in the morphogenesis of plant height and internode length. Plant shape and height were controlled by light quality regulation and R / FR ratio. When the ratio increases, the distance between stem nodes becomes smaller, the plant dwarfs, and the propagating plants tend to elongate. The ratio also has different effects on axillary bud differentiation, chlorophyll content, stomatal index and leaf area. The selective absorption of red light and the selective transmission of far red light make the plants under shade in a far-infrared enriched light environment. The wavelength of ultraviolet light less than 380nm is called ultraviolet light. According to the physical and biological characteristics of ultraviolet, the wavelengths of 320-380nm are long wave ultraviolet (UV-A), medium wave ultraviolet (UV-B) of 280-320nm and short wave ultraviolet (UV-C) of 100-280nm. 95% of the UV species reaching the ground are UV-A. In the solar light spectrum, photosynthetically active radiation, UV and far red light can regulate the growth and development of plants. UV radiation can reduce leaf area, inhibit hypocotyl elongation, reduce photosynthesis and productivity, make plants vulnerable to pathogens, but it can induce flavonoids synthesis and defense mechanism. Low UV-B radiation can cause the plants to grow in vain and hinder the synthesis of plant pigments, which is not easy to cover eggplant and fruit vegetables. One of the important characteristics of plant factory is the lack of UV-A and UV-B radiation in sunlight. The complete absence of UV radiation will bring negative effects on production and affect the growth and development of plants. Therefore, it is necessary to regulate the UV radiation level in plant factory. It is necessary to pay attention to the production demand and response law of plant tolerance.