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Intelligent control promotes new development of agricultural lighting
Although plants can absorb light with a wide spectral range, they also have specific spectral response curves. As shown in Fig. 1, similar to the human eye spectral light efficiency curve V(λ), different plants may also have different spectral response curves. As can be seen from the figure, there is one absorption peak between 400 and 500 nm. There is one absorption peak at 600~700 nm, which is generally considered to be positive for plant growth. 
Agricultural lighting is not a new thing in recent years. The traditional plant fill light has existed before the large-scale application of LED. The light source usually uses xenon lamp, fluorescent lamp, high pressure sodium lamp or metal halide lamp. Although it is intended to increase the line on the absorption peak of plants, the efficiency is still not high. Plants that grow light or plant artificial light need to consume a lot of lighting power, and too much light radiation can not be used by plants. Light radiation is a waste of energy.
The promotion of LED intelligent lighting system has promoted the secondary development of agricultural lighting. In recent years, a large number of LED plant growth lamps have been introduced to the market, and careful analysis of the spectrum has little difference. No matter which product is theoretically more efficient than the traditional light source system. After the completion of the classic demonstration project, flowers and applause can not be exchanged for continuous orders. The reason is that the cost of LED plant fill light system is too high. How can ordinary farmers can afford the initial investment and let the grassroots agricultural technology department promote the plant supplement? The enthusiasm of the light system, like the promotion of high-quality fertilizer and seeds, is a concern and solution for the lighting industry.
Improved traditional light source reduces system cost
LED plant fill light source is usually combined with different proportions of blue LED and red LED according to the needs of different plants. The spectrum is shown by the dotted line in Figure 2. The dimming mode is reduced or increased by the proportion of red and blue light, and the blue and red light modules are controlled by group. Fluorescent lamps are excited by 253.7 nm ultraviolet light, so the initial ratio determines the spectral distribution. The dimming can only be equal-scale dimming, but the plant photosynthesis curve in Figure 1 can be used to reasonably match the phosphor mix and dosage. The fluorescence spectrum is similar to the spectrum required for plant growth, as shown by the solid line in Figure 2.
Comparing Fig. 2 with Fig. 1, it can be found that the spectrally matched fluorescent lamp is closer to the plant photosynthesis spectral response curve in the spectral distribution, and the theoretical efficiency is higher. In theory, LEDs can well match the spectrum required by plants, but the monochromaticity and narrow spectrum of LEDs become their weakness here. Only 430 nm blue and 630 nm red light can not meet the actual spectral modulation requirements, but add some others. Band LEDs increase system cost, and the spectrum of fluorescent lamps can be broadened to some extent, improving utilization efficiency.
In terms of system efficiency, the simplest and straightforward way is to compare the optical radiation power. In Figure 2, the measured 40.4 W fluorescent light radiated power is 11.1 W, the conversion efficiency is 27.5%, and the measured 13.4 W LED optical radiation power is 1.7 W. The conversion efficiency was 12.7%. From the viewpoint of optical radiation power, the spectrally modulated fluorescent lamps shown in the following table have higher conversion efficiency.
The use of photosynthetically active radiant flux (PARflux) has been proposed to more accurately express plant growth and light quality, as shown in equation (1).
Bp(λ) is the response curve of plant growth spectrum, and KBp is corresponding to Km. It is a parameter related to photometric normalization, and its numerical value is related to the peak value of Bp(λ).
At the same time, in order to reflect the influence of photoperiod on plant growth, the time parameter t should be introduced in the actual evaluation of the lighting environment, that is, using the photosynthetic effective radiation dose (PARenergy) to characterize, the dimension is equivalent to the energy unit joule (J) as the formula (2) ) shown.
In order to simultaneously reflect the three variables of spectral distribution, illumination time and illumination intensity, formula (2) is rewritten into equation (3), and the effective radiation dose density of photosynthetic is used to more accurately express the total illumination required for different growth stages of plants. the amount. It can be used as a reference for plant growth refinement operation in plant growth fill light illumination system or pure artificial light planting illumination system, thereby improving system efficiency.
Dimming strategy is the core of agricultural intelligent lighting
For the remote, closed, and whole process intelligent plant fill light illumination system, the variable setting can be easily performed according to formula (3). There are three variables to be set, that is, P(λ) plant fill light spectrum, Bp (λ) Plant growth spectrum response curve, t time. Among them, the existing technical means of P(λ) can be completely solved, that is, the spectrum and intensity of the plant growth light source are adjusted according to the needs, and the key lies in the preset and adjustment of Bp(λ) and t.
According to the type of plants to be planted, an initial value of Bp(λ) can be preliminarily preset, but the adjustment of different growth periods Bp(λ) and the control of the required irradiation time t are different according to actual planting conditions, and image processing can be adopted. The method is compared with the preset software, and can also be controlled by an expert through a remote online method. With the existing equipment on the market, a smart plant fill light illumination system can be built, as shown in Figure 3.
The light source can be dimmed in real time according to the terminal instruction. The light dosimeter can feedback the illumination parameters in real time to adjust the system, and the plant growth condition is transmitted back by the camera in real time to analyze the growth situation and determine the fill light strategy. The hardware of the system is quite simple. It is only mechanically assembled and patched. All components can be purchased directly. The key point and difficulty lies in the software platform support in the background. It can be online mode support or offline software package support. Coupled with the multi-element loading control of water, gas, temperature, etc., it is not a fantasy to control the entire plant factory with one terminal. At least for lighting, there is no difficulty in the prior art.
Agricultural lighting systems involve light sources, luminaires, and controls. These techniques can be difficult, and as long as the cost is controlled within the acceptable range of farmers, these problems can be solved. Only by injecting a dimming strategy in a targeted manner can the intelligent lighting system be vital, which is a task that can be accomplished by multi-unit and multi-disciplinary cooperation. In practical applications, it seems that the current technology and cost, LED agricultural lighting system into large-scale civilian promotion seems to be not realistic. Using a combination of spectrally modified fluorescent lamps and LEDs, large-scale use of fluorescent lamps with obvious price advantages, coupled with a small amount of process-modulated LED light source, reducing the overall system cost may be a feasible way to promote agricultural lighting.
summary
The special application industry of agricultural plant fill light illumination is in the ascendant, and the era of Internet+ has also come. The embedded application of intelligent lighting in the illumination of plant fill light system can push the plant fill light illumination to a higher level, thus achieving plant growth illumination. The refined management has positive significance for improving the level of modern agricultural production, and its market potential is to be explored by people of insight and industry colleagues.
The three major strategies play the role of agricultural lighting
The introduction of intelligent lighting into plant growth makes it possible to carry out remote monitoring, closed and full-process intelligent monitoring and operation according to the growth cycle of different plants, realizing agricultural industrialization, automation and intelligence.