1, red light
Among the visible light, red orange light (wavelength 600~700nm) and blue-violet light (wavelength 400~500nm) are absorbed by green plants, and only slightly absorbed by green light (500~600nm). Red light is the first light quality used in crop cultivation experiments. It is the necessary light quality for the normal growth of crops. The number of biological needs is the first among various monochromatic light qualities, and the most important light quality in artificial light sources. The substances produced under red light make plants grow taller, while the substances produced under blue light promote the accumulation of protein and non-carbohydrate, giving plants weight gain. The far-infrared infrared light reduced the concentration of saponin, carotenoids and chlorophyll by 40%, 11% and 14%, respectively, and increased the fresh weight, dry weight, stem length, leaf length and leaf width by 28% and 15%, respectively. 14%, 44% and 15%. Red light is light-morphized by phytochrome; red light promotes photosynthesis through photosynthetic pigment absorption; red light promotes stem elongation, promotes carbohydrate synthesis, and is beneficial to the synthesis of fruit and vegetable VC and sugar; but inhibits nitrogen assimilation. However, it is still a bit difficult to cultivate plants well with red light alone.
2, blue light
Blue light is the necessary supplemental light quality for crop cultivation, which is the necessary light quality for the normal growth of crops. The amount of light-emitting organisms is second only to red light. Blue light inhibits stem elongation, promotes chlorophyll synthesis, facilitates nitrogen assimilation and protein synthesis, and is beneficial to the synthesis of antioxidants. Blue light affects plant phototropism, photomorphogenesis, stomatal opening, and leaf photosynthesis. LED red light supplement LED blue light can improve the dry matter quality, fractional number and seed yield of wheat, and increase the dry matter quality of lettuce. Blue light significantly inhibited the growth of leaf lettuce stems. Increasing blue light in white light can shorten internodes, reduce leaf area, reduce relative growth rate, and increase N/C efficiency. High plant chlorophyll synthesis and chloroplast formation as well as high chlorophyll a/b ratio and low chloroplast require blue light. Excessive blue light is not conducive to plant growth and development. The red-blue combined spectrum can promote the growth and development of vegetable seedlings more than the red or blue-light monochromatic light. The ratio of red and blue light required by different plants is different.
3, green light
Green light and red blue light can be harmoniously adjusted to adapt to plant growth and development. Generally, under the red-blue LED composite light, the plants are slightly purple-gray, making the disease and disorder symptoms difficult to diagnose, and can be solved by supplementing a small amount of green light. The green light effect is usually opposite to the red-blue light effect, for example, green light can reverse the opening of the pores promoted by blue light. The photosynthetic quantum yield of the upper chloroplast on the near-illuminated surface under strong white light is lower than that of the lower chloroplast. Because the green light is more able to penetrate the leaves than the red and blue light, the lower chloroplast absorbs the extra green light and increases the leaf photosynthesis more than the additional absorption of red and blue light. Low light intensity cultivated plants may not consider green light, low density and low canal thickness facilities plants do not consider green light, high light intensity, high density, high canopy thickness, green light must be considered.
4, yellow light and orange light
Yellow light, orange light, green light, and purple light are all important photosynthesis effective radiation, but the plant demand is small. Adding yellow light to the red and blue light can significantly increase the growth of spinach seedlings. Huangguang has the best effect on improving the nutritional quality of leaf lettuce, but blue light is more conducive to significantly increase the content of mineral elements in lettuce. Adding yellow and violet light can improve the photosynthetic capacity of cherry tomato seedlings and alleviate the red and blue weak light stress. Compared with white light, violet light and blue light increase the activity of antioxidant enzymes, delaying the senescence of plants, while red, green and yellow light inhibit the activity of antioxidant enzymes and accelerate the aging process of plants.
5, far red light
The far-red light of 730 nm has little significance for photosynthesis, but its strength and its ratio with the red light at 660 nm play an important role in the plant height and inter-segment length. The R/FR ratio is used to control plant morphology and plant height through light quality regulation. When the ratio becomes larger, the spacing of the stems of the plants becomes smaller, the plants are dwarfed, and the reproductive plants tend to elongate. The change of the ratio also affects the 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 allow plants under shading to be in a far-infrared enriched light environment.
6, ultraviolet light (UV)
A wavelength band of less than 380 nm is called ultraviolet light. According to the physical and biological characteristics of ultraviolet light, wavelengths of 320 to 380 nm are long-wave ultraviolet (UV-A), medium-wave ultraviolet (UV-B) having a wavelength of 280 to 320 nm, and short-wave ultraviolet (UV-C) having a wavelength of 100 to 280 nm. 95% of the UV species reaching the ground is UV-A. In the solar spectrum, photosynthetically active radiation, UV and far red light have regulatory functions on plant growth and development. Ultraviolet radiation reduces plant leaf area, inhibits hypocotyl elongation, reduces photosynthesis and productivity, and makes plants susceptible to pathogen attack, but can induce flavonoid synthesis and defense mechanisms. Plants with low UV-B radiation cause long growth, hinder the synthesis of plant pigments, and are not easily used to cover solanaceous vegetables. An important feature of plant factories is the lack of UV-A and UV-B radiation in sunlight. The complete absence of UV radiation will have negative effects on production and affect plant growth and development. Therefore, it is necessary to regulate the radiation level of UV in plant factories. It is necessary to pay attention to the basis of production demand and plant tolerance response law.