The vast majority of animals and plants on the earth are inseparable from the sun's rays, but the supply of sunlight is limited and different in different regions and at different times. Avoiding the cycle of illumination, there are still many insufficient light. In the case of artificial light sources, the supplemental light in the growth of animals and plants came into being. Before the LED technology, it mainly relied on high-pressure sodium lamps, fluorescent lamps and other light sources. However, such conventional light sources are very inflexible in terms of spectrum and energy, and due to the diversity of animals and plants, different species may have different artificial light requirements, resulting in artificial The application of fill light is slow to develop.
LED is a rapidly developing lighting technology in recent years. In addition to the light efficiency and longevity, it has great advantages over traditional light sources. The great flexibility of LED in spectral space, time, and scale space has created a huge application prospect for LED in animal and plant fill light. At the same time, in recent years, LED technology has been continuously improved, light efficiency has been continuously improved, and prices have dropped rapidly, which has promoted the substantial progress of LEDs for agricultural lighting. However, due to the complexity of agricultural lighting, the current LED lighting for agricultural lighting is in the stage of continuous trial and exploration. There are many theoretical and practical problems that have not yet been solved. This paper attempts to make some one-sided explanations in these aspects.
First, the multidisciplinary nature of agricultural lighting
If plant lighting and animal lighting are included in the scope of agricultural lighting, the disciplines involved include botany, zoology, biostatistics, lighting technology, and control technology. The first three are the fields of biology, the latter two are the fields of lighting technology, and the subject span is very wide. In these disciplines, lighting technology is a technical means, and the content of biology is the experimental process and the result judgment. In general, knowledge in the field of biology is the most important part of agricultural lighting, but currently agricultural lighting mainly refers to the use of LED lighting technology, and the high flexibility of LED, making the agricultural lighting process, as the main agricultural Or scientists in the biological field need the high cooperation of lighting experts to achieve the best lighting conditions for various animal and plant species, and the successful improvement of the lighting discipline in the field of vision is also worthy of reference for agricultural lighting. Therefore, the discipline and technological advancement of agricultural lighting requires scientists in the fields of agriculture and biology to work closely with scientists in the field of lighting.
Second, the complexity of agricultural lighting
As an agriculture-related science and technology, agricultural lighting inherits the complex nature of agricultural science. As mentioned earlier, it includes two aspects: agriculture and lighting.
The former has studied a large number of species, and each of the species has a lot of conditional factors. For example, the basic elements of plant growth, sunlight, air, and water, in addition to changes in seeds, soil, and surrounding environment such as temperature, humidity, and climate, also affect plant growth. On the animal side, because it is active, it includes more factors. Even if all these conditions are consistent, the growth of individual animals and plants may be different, which determines that bio-statistical methods must be used for agricultural lighting research. the study.
In addition, in terms of illumination, there are also a number of variables, including the spectrum, intensity, time and period of illumination, light form (steady state or pulse), and the like.
The above two aspects determine the complexity of agricultural lighting. Although optimizing the growth of animals and plants by regulating the intensity of light can be carried out under the same conditions, the interaction of various conditions that may exist will make the research problem more complication.
Third, the test difficulty of agricultural lighting
The complexity of agricultural lighting determines the difficulty of the research of agricultural lighting research, which is reflected in the fact that the experimental variables are too many. Despite the main experimental lighting conditions, by studying different light conditions, such as irradiation intensity, spectrum, irradiation time, irradiation period, irradiation mode, etc., it is expected to fix other agricultural conditions such as temperature, humidity, air, Moisture, nutrients, seeds, etc. However, these two kinds of factors may affect each other. Therefore, in actual experimental research, there are many experimental changes to be considered, and each condition must have a certain sample for biostatistical considerations. This makes the test conditions more, more samples, plus each test condition requires a certain growth time, and finally caused the situation of agricultural lighting research: the test sample is very large, the test time span is very long, agricultural lighting becomes time-consuming and laborious Research on the cost of space. As an example, if three kinds of illumination condition variables, such as spectrum, intensity, and illumination time, are used, and each variable uses 10 discrete values, it can be seen that there are a total of 1,000 conditions, and if there are 10 biological conditions, that is 10,000. In the case, if there are 10 samples in each case, it is 100,000 samples. If each sample is to be carried out for 2 months, then the difficulty of this test can be imagined. Therefore, the actual research is forced to reduce the number of test variables and reduce the number of variables in each test. When reading the relevant literature, I often find that the illumination conditions used are only within 10, and there may be test conditions used. Optimal, and therefore cannot find the best results.
The Dendrobium Dendrobium fill test, which was reported in the past, consisted of 6 seedbeds (one acre) in a greenhouse, and installed and commissioned 153 LED lamps and 8 fluorescent lamps, marking 644 samples. The data collection was carried out for 7 months, and 3 batches of nearly 200,000 data were completed, and the best lighting conditions were obtained through analysis. The scene is shown in Figures 1, 2 and 3.
As can be seen from Fig. 3, in the 113 different light environment combined environments, only the two experimental conditions showed the best growth of Dendrobium candidum, and the two growth conditions were significantly better than the rest. Under the other 111 kinds of light conditions, the growth was not much different than that of the fluorescent control group and the non-illuminated group. It is conceivable that if 10 or 20 conditions are tested, it is likely that no optimal lighting conditions can be found.
Before the LED, a lot of research was done on the light supplementation with the traditional light source. However, due to the lack of flexibility of the traditional light source, it is difficult to achieve a variety of lighting conditions, and often only a few simple lighting conditions can be studied, as mentioned above. More than 10 kinds are often used. Therefore, in the case that LEDs are easy to implement various lighting conditions, it is of great practical significance to re-detail research and screen the best lighting conditions.
Fourth, the light selectivity and spectral weighting of agricultural lighting
Agricultural lighting is generally considered to be spectrally selective, as is visual illumination, and thus there is a weighting curve similar to the spectral viewing function in visual illumination. The often cited curves are shown in Figures 4 and 5.
The study of the human visual function has also been obtained after a large number of experiments. Due to the small differences in the races, the visual function is currently widely used. However, the weighting function of plant illumination has a limited theory, and the chlorophyll spectral absorption rate of the plant of Figure 5 is more and more questioned. In fact, looking at the differences in the spectral reflectance of the foliage of various plants, it is easy to imagine that the photosynthesis weighting functions of different plants are likely to be different, so there is a lot of research work to be done. After completing the photosynthesis spectral weighting function of various plants, the concept of "light flux" can be established with reference to visual illumination, that is, the conversion of radiant flux to photosynthesis physical quantity, and the corresponding testing means are completed.
Animal lighting is similar to plants, and there is a corresponding research work to be done.
V. Diversity of evaluation indicators
In the lighting discipline, visual science is the science of studying light acting on the human eye. The main evaluation indicators are visual clarity and comfort, and include indicators such as illuminance and brightness. The latter are indicators such as glare and stroboscopic. When entering the agricultural lighting, the indicators of concern are more complicated, including the growth of plants, the content of certain components, etc. Further refinement can be the leaf area, rhizome, total height, color, etc. of the plant, including sugar, chlorophyll, etc. Indicators. In fact, there are many other indicators, such as increasing the growth of plants by supplementing light, or suppressing the growth of certain things in turn, which has another type of evaluation index.
Animal lighting evaluation indicators are also complex and diverse, such as for the growth of broiler light, the evaluation indicators can be the growth rate of chicken, but also meat quality, protein content, etc., can consider the chicken sales perception and mortality, and even chicken The situation of the feathers and so on.
The complexity of the evaluation indicators has increased the difficulty of agricultural lighting research. It is worth mentioning that, due to the use of multiple lighting conditions, and different growth stages may require different fill conditions, agricultural lighting is often combined with control technology, that is, through control technology, complete control of the entire lighting.
With the advancement of LED technology, the improvement of performance and the further decline of price, it is believed that LED will have great application prospects in agricultural lighting, but it is necessary to carry out scientific research to complete the exploration of lighting optimization conditions, in view of the above analysis of agricultural lighting. The difficulty requires the close cooperation between agricultural scientists and lighting scientists.
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