Urban night scene lighting refers to the night lighting of all outdoor spaces or sceneries in urban areas; if the night scene lighting uses artificial plant light, what impact will it have on plants? Will it promote the growth and development of plants? Will it make viewing plants more beautiful? This is a very interesting subject, worthy of further investigation.
Commonly used are night landscape lighting, road and traffic lighting, square or construction site lighting, advertising sign lighting, and garden landscape lighting. Common light sources for night scene lighting include incandescent lamps, mercury lamps, fluorescent lamps, metal halide lamps, high-intensity gas discharge lamps, LED lamps, etc. In the process of urban planning and construction, lighting and green plants are often combined for arrangement and construction. According to different environments, plants and light sources have different combinations to achieve night lighting and beautification.
Plant’s demand for light characteristics
In the process of plant growth, illumination, light quality, and photoperiod will all affect it. Studies have found that under low light, increasing the light intensity can increase the photosynthetic rate, but when the light intensity increases to a certain value, it will no longer work. At this time, the factors that affect plant growth become temperature and carbon dioxide concentration. Red light and blue light are the two most important light in plant growth, and the ratio of red to blue luminous flux (R/B ratio) will affect the cultivation effect of plants, and other colors of light will also affect the growth of some plants to a certain extent. In addition, the photoperiod will also affect the growth and development of plants. At present, there have been many research reports on the “mechanism of the influence of photoperiod on plant growth and development“. Many of these studies have explored the mechanism of light-induced flowering in order to achieve effective regulation of the flowering period of ornamental plants.
It can be seen that the application of LED artificial plant light to plant lighting requires consideration of the design of the light source from multiple aspects to meet the lighting requirements of light-receiving plants.
The impact of artificial plant light on landscape plants
Landscape plants are an important part of the night scene. Without landscape plants, the night scene will become lifeless. At the same time, reasonable use of night lighting will make landscape plants more colorful and enjoyable. LED artificial plant light has many positive effects on the growth and development of plants. If landscape plant lighting is changed to artificial plant light, there will also be some positive effects. These effects may not be as obvious as indoors, but they also leave us with A lot of imagination.
The effect of artificial plant light on seed germination and seedling growth of landscape plants
The photoperiod has an important influence on plant and plant tissue culture. Illumination time affects the germination of seeds. The germination rate of seeds under long-day conditions will be higher than that under natural conditions. This is due to the distribution and accumulation of more assimilation products to seeds under long-day conditions. At present, the plants planted in urban public spaces are basically transplanted. From the growing place to the transplanting place, the photoperiod of different plants is unified, which may have a certain impact on the seedling and seed formation of certain landscape plants. The wavelength of artificial plant light is close to that of natural light, which undoubtedly increases the photoperiod, and the time for plants to receive the available light is greatly extended, which will accelerate the accumulation of plants and promote the germination of plant seeds and the growth of seedlings.
The impact of artificial plant light on the nursery of landscape trees
Trees are the main plants for urban greening, and they undertake the important tasks of purifying the air, absorbing greenhouse gases, and creating a livable environment. According to previous studies on certain tree species, prolonging the light time can promote the growth of seedlings and inhibit dormancy. On the contrary, shortening the light time can inhibit the growth of seedlings and promote the formation of apical buds. Therefore, supplementing light for some seedlings can promote their growth and shorten the nursery.
Time to improve the efficiency of seedling raising. Extending the light time to the seedlings of red-skin spruce will promote the growth of the tree. The greening trees on both sides of urban roads are often arranged at intervals with street lights. The growth of the leaves of the trees that can be illuminated by the street lights is different from the growth of the leaves of the trees in the shadow area. This difference varies with the type of trees. The irradiation of artificial plant light is a supplement to sunlight, allowing plants to photosynthesize at night so that landscape trees will accelerate the growth rate, speed up the rate of seedlings, and increase the rate of seedlings.
The impact of light intensity on landscape plants
Light intensity is an environmental signal, which affects the growth and development of plants through phytochromes. Due to the presence of night lighting, the light intensity received by the plant leaves is different from the light intensity in the natural state, so it will have a direct impact on plant growth. There is an upper limit to the demand of light intensity by plants, which is the light saturation point. When the light intensity reaches the upper limit, photosynthesis reaches the strongest. When the upper limit is exceeded, the plant will produce photosynthesis and reduce the photosynthesis of the plant.
Due to the needs of urban lighting, urban night scene lighting tends to provide strong light intensity for urban green plants, among which shade-grown and partial-negative plants are most affected. The light intensity of artificial plant light can be adjusted freely, and it can be adjusted to the light saturation point of the plant corresponding to different plants, which will promote the development of plants, but we know that the intensity of night lighting is not arbitrarily adjusted and requires light pollution. Comprehensive considerations such as pavement lighting and energy utilization, and the light intensity of artificial plant light need to be weighed to make a reasonable choice.
The impact of light quality on photosynthesis of landscape plants
Light quality affects the photosynthesis of plants through chlorophyll. Chlorophyll content reflects the ability of plants to absorb and transform light energy. It is an important indicator for evaluating plant growth and development. Different light quality has different effects on plant chlorophyll content. Many studies have shown that white light and red light promote the increase of plant chlorophyll content, while blue-green light inhibits the increase of plant chlorophyll content. However, some studies have shown that the chlorophyll content of some plants under blue light treatment is higher than that under red light treatment. Therefore, the effect of light quality on plant chlorophyll content varies with plant types and tissues, and organs.
In addition, the photosynthesis rate is an important indicator of photosynthesis. Some studies have shown that blue light can increase the value of the net photosynthetic rate of chrysanthemum leaves, while red light will reduce the value of the photosynthesis rate; some research results show that red light promotes plant leaf photosynthesis, while blue light inhibits plant leaf photosynthesis. The results of the analysis may be due to the different degrees of adaptation of the selected species to light quality, resulting in different effects of light quality on leaf photosynthesis.
The wavelength of artificial plant light is fixed, and the color of light is also fixed. Before making a choice, we need to make full research preparations for local plants and choose a good light color. Of course, the choice of light color also needs to be related to the view. It is also important to match the trees to make the scenery look beautiful.
The effect of light quality on plant growth and metabolism
Studies have shown that red light can promote the growth of certain plant seedlings, promote lateral branching and tillering, and delay flower bud differentiation, while far-red light can eliminate this effect; blue light can inhibit the growth of plant leaves, reduce leaf area, and reduce plant growth. Growth rate. The content of carbon and nitrogen metabolites in plants is also affected by light quality. Studies have shown that blue light helps protein synthesis and red light helps increase carbohydrates. Xie Baodong et al. studied the leaves of Ginkgo biloba and found that the light quality has a significant effect on the metabolite content of plants in this life.
History and current situation of artificial plant light
In the 1980s, Japan began to study the application of LEDs to plant growth, but did not make a breakthrough in the application of high-brightness blue chips, and only used 660 nm discrete LEDs. In the mid-1990s, NASA began to screen and develop LED light sources and apply them to plant tissue culture. High-brightness GaN-based LEDs came out in 1989, which further promoted the development of III-V compound LEDs. In recent years, there have been a large number of studies reporting the relationship between illumination, light quality, and photoperiod and different crop growth forms, and corresponding optimization design schemes for illumination, light quality and photoperiod have been proposed. Table 1 shows the specific application of LEDs in plant lighting.
In terms of improving the function of LED plant light, the method proposes that the uniformity of lighting can be improved by changing the arrangement of LED particles. In addition to the content of optical design, researchers have also carried out a series of studies on the driving circuit, control system, and equipment structure of lighting equipment. For example, LED intelligent lighting biological incubators, LED plant growth boxes, MOKOLight LED plant light, and solar-powered LED light control systems, and other plant lighting systems or equipment.
At present, many kinds of artificial plant light are in use, but LED has the fastest development speed and the broadest prospects, and it is already rapidly replacing other solutions. As far as the actual situation is concerned, it is still difficult for plant lights to meet the needs of modern agriculture, but only meet the needs of a small number of high value-added plants, so we still need to continue to develop.
Conclusion
The research on the influence of urban night scene lighting on landscape plants needs further study. For example, the main roads in the city will use high-power streetlamps because of the lighting needs. At the same time, considering the range of illumination will increase the height of the street lamps, the night lighting will have an impact on the urban green belt plants on both sides of the road. Because there are many types of landscape plants and the green plants in cities in different regions are also different, large-scale research is unrealistic. When doing research in this area, it is necessary to determine the research area and research plants and conduct on-site investigations and experimental analysis to be able to reasonably and effectively reflect the impact of night lighting on certain landscape plants.
