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When installing artificial light sources, they should be placed at a specific distance directly above the plants being illuminated, with a minimum distance of approximately 10 cm. Since the LED light source emits cold light, it will not cause harm to plants.
Side fill light between plants
When using top fill lighting, the leaves at the top of the plant may block the light, resulting in insufficient light for the lower leaves. Side supplementary light between plants can help improve the light distribution in the vertical direction, speed up the photosynthesis of the lower leaves, and thereby improve the utilization efficiency of light. Research shows that there is no significant difference in tomato yield and quality whether LED side fill light or high-pressure sodium lamp top fill light is used, but LED side fill light can save 36.3% of energy. Therefore, LED light sources are very suitable for side fill light.
photoperiod control
Photoperiod control refers to controlling the light time of plants through indirect light supplementation or shading, thereby affecting the flower bud differentiation of plants. The photoperiod must be determined according to the type of plant (long-day, short-day, day-neutral plants). For long-day plants, artificial light can be used to extend the lighting time to promote flowering in the short-day season; for short-day plants, shading treatment can promote flower bud differentiation, while extending the lighting time will delay flowering. For most crops, it is necessary to ensure at least 4 hours of dark period every day, otherwise photosynthetic products will accumulate in the leaves and reduce light energy utilization efficiency.
Current research status of artificial light regulation of plant growth and development
In an artificial environment, irradiating plants with artificial supplementary light or full artificial light can promote plant growth, increase yield, improve product form and color, and reduce the occurrence of pests. With the development of artificial light source technology, the use of light quality to control plant growth and development has become a new control technology. The study found that under the same light intensity, the leaf area and petiole length of strawberry increased significantly when covered with green film and red film, but the leaf area and petiole length decreased significantly when covered with blue film. Blue light and ultraviolet light will reduce the area of grape single leaves, while red light treatment can significantly increase total dry matter accumulation and promote thicker growth of new shoots. Supplementing green light with red and blue light can slow down the degradation of chlorophyll in lettuce leaves and increase the chlorophyll content in tomato seedlings, thus promoting the growth of the seedlings.
On the one hand, the development of light control technology relies on the advancement of artificial light source technology, and on the other hand, it also promotes the development of artificial lighting systems. Traditional artificial light sources include high-pressure sodium lamps, metal halide lamps, etc.
The main emission spectrum of high-pressure sodium lamps is concentrated between 560 and 640 nanometers, which is not completely consistent with the spectrum of photosynthetically active radiation of plants (400 to 700 nanometers). It is usually used to extend the illumination time of plants to increase yields. But early high-pressure sodium lamps lacked the blue light crucial for plant growth. After improvement, although it has had some negative effects on plants, such as reducing chlorophyll content and dry matter synthesis, etc.
The dense spectrum (380~780 nanometers) emitted by the dysprosium lamp in the metal halide lamp is quite close to the solar spectrum, and has high luminous efficiency (>75 lm/W) and color rendering (Ra>80), but its The effective photon beam density is lower than that of LED, which is not conducive to the photosynthesis of plants.
LED lights can not only emit monochromatic light with narrow light waves, but can also combine light sources in any way according to the needs of plants, which has obvious application advantages in the field of plant lighting.
summary
Whether from the perspective of promoting the development of modern agriculture or realizing energy conservation and environmental protection, LED plant lighting is of extremely important significance. The status and development needs of agriculture provide new opportunities for the development of LED plant lighting. Since 2013, the global LED plant lighting market has entered a stage of rapid development, mainly concentrated in North America, Japan, the Netherlands and other regions. In 2010, Japan's Mitsubishi Chemical used large containers to transform plant factories and use LED light sources for photosynthesis. In 2012, the first LED lighting plant factory system was used to cultivate lettuce and young leafy vegetables, opening a new chapter in LED plant lighting. According to LED inside statistics, the global LED plant lighting market size was US$100 million in 2014, grew to US$575 million in 2016, and is expected to increase to US$1.4 billion by 2020.
Domestic plant lighting is still in the early stages of industry development. The small scale, small number of manufacturers, lack of core technologies and unified standards and specifications are bottlenecks in the development of domestic plant lighting technology.
In order to promote the healthy and sustainable development of the LED artificial plant lighting industry, it is necessary to start from the following aspects:
(1) Plant lighting is a professional, comprehensive and interdisciplinary technology, so it requires comprehensive, systematic and in-depth research on LED light sources and botany.
(2) Standardization work is an important means to promote the industrialization of scientific research results and support the development of industrial standards. Therefore, it is necessary to accelerate the formulation of standards and improve the standard testing and certification system.