LED illumination intelligent control system in plant factory: a review

Research
Md Ashrafuzzaman Gulandaz13Mohammod Ali2Shafik Kiraga1Sun-Ok Chung12Soon Jung Hong3Soon Jung Hong4

Abstract

Light-emitting diodes (LEDs) are broadly used in smart agriculture especially in plant factories because of energy efficiency and variable spectrum characteristics. LEDs can promote plant growth and photomorphogenesis that improves plant yield and quality in the control environment. The objectives of this paper were to review the advantages of LEDs on phototrophic plants, different light detection systems, and intelligent control systems of LED illumination on plants inside plant factories. The typical LEDs supplement light devices and intelligent control systems that are regulated by various control models. The narrowband LEDs with the simplest combination of wavelengths can optimize light and promote photosynthesis. Blue light is advantageous for chloroplast improvement and can increase the amount of chlorophyll in algal cells. Red light is the best light source to keep short-lived plants from blooming and sometimes helps plants bloom in dark times when distant red light can counter the effects of red light. The review demonstrated that fuzzy logic control systems are more reliable compared to other intelligent control methods such as intelligent machine vision, wireless intelligent control systems, and PID control. The future development direction and application prospects of LEDs with intelligent control are addressed for ensuring the quality and productivity of cultivating plans inside the plant factories.

Keyword



Introduction

The plant factory is a facility that helps producers to grow plants by artificially managing the environment (e.g., light, temperature, humidity, carbon dioxide concentration, and culture solution) which is shown in Fig. 1 ( Saya et al., 2018). This allows gardeners to produce high-quality veggies all year. Plant factories can grow vegetables two to four times faster than traditional outdoor farming by managing the indoor environment. Furthermore, because many cultivation shelves (a multi-shelf system) are used, bulk vegetable production in a limited space is made easier. The role of plant factories is illustrated in Fig. 2 (Kozai, 2016).

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Fig. 1. Plant factory facility (Saya et al, 2018)

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Fig. 2. Role of plant factories in agriculture (Kozai, 2016)

Light is controlled appropriately to maintain the optimal environment for photosynthesis, trigger improved productivity, improved stability, improved safety, improved functionality (Poulson and Thai, 2015). LED light illumination is one of the most important parameters for crop production. LEDs have the potential to be used as both supplemental and sole-source lighting in glasshouses and plant factory systems, where plants are cultivated indoors under controlled climatic conditions (Bayat et al., 2018). LEDs provide a number of advantages, including linear photon output, durability, and a long operational lifespan, as well as the potential to be built into enormous arrays that produce high Photosynthetically Active Radiation (PAR) for plant growth and development. LED modules also produce less heat than older lighting systems like High-Pressure Sodium, Halide, and Fluorescent tubes (Kozai, 2016). Such an arrangement will assist agriculture to get rid of assets and environmental limitations and ensure sustainable agricultural development.

It is quite difficult to produce crops firmly due to environmental changes (UN, 2014). Consequently, expectable and consistent yields are difficult to achieve (Newcombe et al., 1979; Rosenzweig et al., 1992). Because of the different bottlenecks like drought, salinity, flood, etc. in agriculture; plant factory is getting popular for crop production day by day (Islam et al., 2021).

The system practices a high-precision environment to adapt to the indoor climate, reduce lighting, temperature, and proportion, and integrate intelligent control, contemporary industry, biotechnology, nutrition solutions, agriculture, and technology of information to achieve high precision implementation. Control of environmental aspects so that plant growth is hardly limited by outward natural situations (Lambin et al., 2011; Newcombe et al., 1979). The aim of the industrial plant production system is to provide high-quality horticultural products with high quality and cleanliness.

Currently, maximum crops and herbs are not only sold in huge superstores but also in the foodservice industry. In these industries, plant factory produced vegetables are free from pesticides, pollutants, and insects which greatly reduces the cost of hygienic processing (Brandon et al., 2016; Rosenzweig et al., 1992). Therefore, factory plants are considered as an important way to solve problems like the shortage of new generation workers in the future in view of the shortage of resources and high demand for food. Food self-sufficiency has been widely praised by countries throughout the world for its usefulness in future space engineering exploration.

Japan, Netherland, and China are the most represented countries in the world whereas Japanese development of artificial light plant factories is relatively fast and pioneering (Kozai et al., 2006). Although basic science and technology are equivalent, most of the technologies used in artificial lighting (PFAL) plant factories are different from those used in horticulture and agriculture. Therefore, new thoughts are needed for PFAL technology, such as uplifting systems, the use of green LEDs, a hydroponic growing system with limited core mass, year-round production, and the use of natural energy in PFAL.

Plant Factory (PFs) uses Single Source Lighting (SSL) for inside crop production. SSL is a technical factor that limits the development of the PF industry. Over the past decade, light-emitting diode (LED) technology has advanced to the point of global commercial adoption (Kozai, 2013). LEDs control the photosynthesis of the granules, controlling the spectral emission of photons that were not previously present. The history of the use of LEDs in grain production is studied, including research on the role of different bands in plant response control and the growth of next-generation LED illuminators with improved grain production control functions with improved quality characteristics (Sezina et al., 1999).

The use of LEDs as lighting devices has become popular because of their energy-efficient properties (Kozai, 2013). However, LEDs have a relatively small radiation angle compared to other types of lighting devices. This changes the intensity of light obtained at a particular segment near the LED. Light detectors are designed to convert low light levels into an electric signal of reasonable amplitude to avoid deterioration of the signal by external noise or pick-up. The photoresistor is a term that is sometimes used to refer to photoconductive devices. They convert changes in incident light into differences in resistance, with resistance decreasing as the intensity of light increases. To achieve homogeneity of light intensity, an opaque logic control system model is used to control the LED lighting in the room (Goto, 2012). This model has several apparatuses: LED lamp, LED driver, light sensor, micro-controller, and differential RS-485 transceiver. The symbolic reasoning system used lighting error and lighting delta error as input parameters in this model. This method changes the duty cycle of Pulse Width Modulation (PWM) into an output where the LED cannot control the lighting of the lamp. Using this model, the system is expected to provide homogeneity in light intensity throughout the room. Finally, the objectives of this paper were to review the advantages of LEDs on phototrophic plants, different light detection systems, and intelligent intensity control systems of LED illumination on plants inside plant factories.

The advantages of LED lighting

Light plays an important function in regulating plant development and metabolism as an important physical environmental component. One of the most distinctive features of this plant is that full artificial lighting with intelligent control of the lighting environment accordingly (Lambin et al., 2011) has now become a common piece of stuff in the industry. Light sources used in plant factories mainly consist of high sodium lamps, metal halide lamps, light bulbs, etc. A major drawback of this technology is the requirement of higher energy for artificial light which is used in photosynthesis. Among the listed lights, LEDs have become very favorable light sources for lighting plant factory crops.

The benefits of high radiation efficacy have been found in LEDs which are long lifespan, small size, low temperature, narrow spectrum, strong physical robustness, and strong attractiveness (Kozai, 2013). The use of narrowband LEDs with the simplest combination of wavelengths can optimize sunlight and promote photosynthesis (Darko et al., 2014; Kozai et al., 2006).
As an alternative to solid-state semiconductor lights, LEDs have unparalleled optoelectronic advantages. Tunable spectra can modulate the range according to power plant growth and improvement needs, using on-demand lighting, high biological light efficiency (Robert, 2008). Cooling light sources can be closed to power plant irradiation to improve space utilization. It is controllable and allows precise control of luminosity and photoperiod suitable for factory production (Tamulaitis et al., 2005). (). Variety of LEDs light source devices (lamp boards, lamp belts, lamp tubes and bulbs), appropriate for protective horticulture because of environmental protection, energy saving, long life, small size and lightweight (Graamans et al., 2017; Kim et al., 2004).

Currently, panel lights for plants, strip lights, lamp tubes, lamp belts, and other lamps that promote appliances are all available. The presence and quality of crops cultivated in different environments are mostly determined by physiological factors. Among the functional factors, light is the most important. As mentioned light plays several such as ensure photosynthesis in plants, control various methods for morphogenetic signaling in plants, prompt several light-dependent biochemical reactions.

LEDs can provide a comparatively cheap lighting atmosphere for plant growth, which is well suited for plant equipment in multi-layered cultivation. Plant morphology, photosynthetic rate, metabolism, and DNA are all affected by the light environment in plant factories (Poulson and Tai, 2015).

Effects of light intensity on plants

Plant photosynthesis is mostly influenced by light intensity. Plants' respiration rate is higher than their photosynthetic rate in low light situations. However, as the intensity of light increases, so does the rate of photosynthesis in plants. Plants begin to accumulate organic matter when the carbon dioxide taken by photosynthesis equals the carbon dioxide emitted by respiration. The offset of sunlight is the current intensity of light.

For instance, the intensity of light continues to increase, photosynthesis in plants is gradually increasing. Therefore, when plants are growing in a plant factory, sunlight provided to the plants should be closer to the saturation level of sunlight for the plants. Plants are divided into sheep plants, neutral plants, and shade plants according to the light saturation dimension. Such as, the artemisinin content is increased in medicinal plant tissue culture. It obviously increases the intensity of sunlight. The increase in light intensity also brought oxidative stress, which augmented the absorption of reactive oxygen species (ROS), and thus increased artemisinin content (Ghasemzareh et al., 2010).

However, in the case of several pharmaceutical plants, the consequence of sunlight intensity on the materialization and addition of medicinal substances is different, some encourage the accretion of medicinal substances, and others constrain the accumulation of medicinal substances (Gasemzareh et al., 2010). In-plant cultivation, photosynthesis often begins at photosynthetic photon flux density (PPFD) levels of 20 μm-2 s-2 and occurs individually up to 1,000-1,500 μm-2 s-2. (Kuznetsov and Dmitriev, 2006) The flow range of photosynthetic photons for which light acts as a signal is much wider. Photoreceptor responses (mainly plant pigments) are classified into three kinds: very weak binding reactions, weak binding reactions, and strong binding reactions (Kneiss et al., 2008). Some cultivars have been shown to adapt better to low light situations, while others use high PPFD (Casal et al, 1998).

Currently, it is very difficult to accurately determine the PPFD content to transmit a chlorophyll retrograde signal. Because it relies on the type of plant we're working with, as well as the growing conditions and the types of reactions it produces (Stutte et al., 2009).

The dry weight of lettuce was generally increased when lettuce was kept at 100 µmol µm-2 μs-1 using red LED (660 nm) and blue LED (450 nm) (Stutte et al., 2009) When the last red LED (640 nm), blue LED (440 nm), and PPFD stayed at 300 μm-2 s-2 (Furuyama et al., 2014), the anthocyanin, antioxidant potential, and leaf area of ​​lettuce were increased. Table 1 repersented the Some examples of different PPFD and their effect on plants (Samuolien et al., 2012).

Mustard and spinach vitamin C is increased by using a red LED (638 nm) and a high-pressure sodium lamp (HPS) and maintained at 300 μm-2s-2 PPFD (Artures et al., 2012).

The phenolic, tocopherol, and antioxidant capacities of la lettuce are increased by appending HPS values ​​of 300 μmol m-2 s-2 under conditions corresponding to hard and fast values ​​of 210 μmol m-2 s-2 (Samuolien et al., 2012).

Table 1. Some examples of different PPFD and their effect on plants (Samuolien et al., 2012). http://dam.zipot.com:8080/sites/pastj/images/PASTJ_21-022_image/Table_PASTJ_21-022_T1.png

The most widely used PPFD bands in the field of plant farming are: The first band is 200-250 μmol m-2μs-1, while the second is 500-800 μmol m-2μs-1. In general, the last value is heavily influenced by the crop's leaf area index (Knight and Mitchell, 1983). The PPFD is affected by the distance between the factory and the LED. Predicting the PPFD is quite difficult. The PPFD forecasts a significant reduction in both power plant demand and the cost of electricity. The PPFD level plants used for planting can range from 10 to 210 μmol m-2 μs-1, depending on the plant type, density, growing conditions, and optimization criteria chosen. The optimum measures are chosen based on the unique goal of developing the plant. Leafy vegetables’ superior growing efficiency could be a factor.

Effect of photoperiod

Photoperiodism is the ability of plants to adapt to seasonal changes in their environment by responding to changes in day length. . In particular, flowering is the most well-studied example of photoperiodism in plants, but additional daylength responses include bud dormancy and bulb or tuber initiation. (Kopsel, 2006). Long photoperiods encouraged muller breeding, including leaf area, leaf chlorophyll content, fresh weight, and dry weight. With this in mind, extending the photodiode to 24 hours reduces this effect (Craker et al., 1983; Warrington and Norton, 1991).

For example, long-term photoperiodic plants such as wheat, spinach, and poplar require 14 hours of sunlight to bloom. Rice, corn and sorghum are examples of short-range photoperiod plants that require fewer than 10 hours of sunlight to blossom. Photoperiods, particularly the length of the night, have an important influence on plant development in most systems. Artificial illumination can assure maximum yield for a particular number of crops. As a result, extending photoperiod length by maximizing and developing plant biomass has a significant favorable impact on plant growth. When the photoperiod is raised from 16 to 24 hours, total radiation increases by 50%, and the weight of all types of pine leaf lettuce doubles (Lactuca sativa L.). Plants exposed to continuous radiation are 30-50 percent higher than plants exposed to 16 hours of light for the same total daily radiation dosage (in moles of photons) (Sirtautas et al., 2011). It should be noted that this outcome is obtained with low levels of PPFD.

In contrast, the effects of photoperiods on plants depend on the individual species and cultivar. In general, PPFDs and photoperiods affect plant growth and improvement. The photoperiod power plant determines the power plant development in response to the photoperiod (Berkovich, 2017).

Effect of the spectral composition of light

Photosynthesis and morphogenesis in plants have a significant impact on light and spectral distribution. During long-term evolution, the plants of the world adapt to continuous radiation, and each species has different selective light absorption characteristics (such as chrysanthemum) in the 400-490 nm and 660-680 nm bands, and the chlorophyll extract is near the maximum absorption band, respectively. 6 (Bayat et al., 2018; Theoharis et al., 2015). LEDs can provide different types of unique light needed for plant growth. After combining several monochromatic LEDs, the spectral elements fit the spectra necessary for photosynthesis and morphogenesis in various plants with a spectral region width of 20 nm. As a result, using LEDs as light sources in power plants can enhance the efficacy of plants that use light energy and save a lot of energy (Wallen and Jean, 1971). Blue light has varying degrees of effect on the chlorophyll concentration of plant cells, depending on the kind of plant or the tissues and organs of the same plant. Blue light is beneficial for chloroplast enhancement and can increase the amount of chlorophyll in algal cells, according to numerous studies (Dorai, 2003; Wu, 2016).

Both blue-violet and ultraviolet light can stop stem cells from evolving. Plants' luminosity can be controlled by blue light with a higher luminous intensity (more than 100 mol m-2 s-2) weakens the luminosity. Plants' brightness is increased by blue light with low light intensity (less than 100 mol m-2 s-2). In low images of the natural environment, phototropism promotes plant development by managing and coordinating the propagation of reactions that enhance the photosynthetic efficiency of artificial photosynthetic light (Takeemia, 2005). Red light is the best light source for preventing short-lived plants from flowering, and it can also assist plants blossom in the dark when distant red light can offset the effects of this red light.

Different spectral aspects of light can change the hormonal composition of plants and affect hormone transport in both active and passive ways. In lettuce, the combination of LEDs has been shown to alter photosynthesis, growth, and morphogenesis rates. Unlike photosynthesis in other plants, sunlight in the yellow-green spectrum enhances the photosynthetic rate of crops greatly, because light can reach low levels of closed cultivation. (Mizuno et al., 2015). Chlorophyll absorbs less green light than red or blue light, allowing more green light to reach the leaf's bottom layers. The slope of green light is, therefore, less dramatic than that of blue or red light (Patushenko et al., 2015).

The extinction coefficients of different wavelengths of light in the leaves depend on the formation of the leaves and the formation of the leaves depends on the physiological structure of the species and the intensity of light during the formation of the leaves. (Nishio, 2000). It should be emphasized, however, that the crop composition has an impact on the crop, which is dependent on the position of the radioactive flux in the case of plant peaks, leaf area indicators, and radioactive flux.

Some experiments have shown that when the photosynthetic photon flux density (PPFD) increases towards the saturation point of light in the chloroplast, it is noticed that mixed light (red and blue) is perceived in this temporary form gradually decreases. The effectiveness of white light is very important for the growth of thermal plants, as it is almost inseparable from the green light. It is more convenient than blue-red light, which penetrates deep into the leaves and absorbs the underlying chloroplasts, which can enhance photosynthesis, thus sweetening plant growth. It should be noted that this occurs during plant growth under white light and high PPFD (Patushenko et al., 2015).

The effect of the blue to the red LED ratio on leaf form, plant growth, and antioxidant phenolic buildup in red and green tendril lettuce cultivars has been evaluated by scientists. Many studies have found that combining red and blue light reduces nitrate accumulation in lettuce, which is important for lettuce cultivation and growth, as well as producing greater biomass (Terashima et al., 2009). Because they are the primary source of energy for photosynthetic CO2 absorption, red and blue lights have the greatest impact on plant growth (Lin et al., 2013). Light quality has a more complicated effect, with inconsistent results. Furthermore, different plant species have distinct spectrum demands and photosynthetic responses, thus they must be studied and established.

LED lighting system in plant factory

Liftable lighting system

Photosynthesis is required for plant growth (Yamori, 2013; Yamori and Sikanai, 2016). Crop development and morphogenesis are intricately linked to the amount of sunlight and the regularity of that light. It's ideal to use an LED light source in the form of a flat-screen with equally spaced LEDs to improve light dispersion between plants. LED panels are frequently positioned along the perimeter or inside the cut, either horizontally or vertically shown in Fig. 3 (D'Souza et al., 2015, Zhang et al., 2015 ).

A plant factory with a changeable light height has been successfully designed by Japanese scientists. The factory employs a mechanical hinge construction to fix the lamp tube to achieve the vertical movement of the LED light source, as illustrated in Fig. 4(a), so that the horizontal movement of the X-shaped steel frame is in the anode and the motor reverses direction at the same time. The brightness of the LED lights is converted, and the vertical lifting of a microcontroller (MCU) is solved to address the illuminance distribution and temperature uniformity of the crop blades. (Seginer et al., 2006).

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Fig. 3. A supplemental upward lighting system (Zhang et al, 2015)

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Fig. 4. Different types of the LED lighting system: liftable LED lighting devices (a), China a new mobile lightfilling device (b) cylindrical lighting system (c) (Jyotsna et al, 2017).

A plant factory cultivation system combining down-lighting and up-lighting has been newly proposed, which significantly increases lettuce yield by reducing the shade of the inner leaf, slowing the aging of the outer leaf, and improving photosynthesis (Jyotsna et al., 2017). Up-assist lighting amplified the curvature coefficient of the photosynthetic photo response curves, providing the possibility of culturing solar-type species under relatively low down-illumination with up-assisted lighting.

Mobile lighting system

China's Beijing Kingfeng International High-tech Corporation succeeded in launching a novel portable lighting charging device in 2017. This gadget, as illustrated in Fig 4(b), can automatically modify the fill height in real-time to meet crop growth requirements. The adjustment device is installed in a three-stage light source lifting type stereo cultivation, with the highest light level on the top layer of the device and a high-pressure sodium lamp. The middle and lower floors are equipped with raising and lowering devices, as well as LED lighting. It corresponds to the light sensor's detection signal. It automatically adjusts the height of the daylight to provide the crop with the proper lighting conditions. After that, a system for coordinating sunlight within the plant was implemented, and the suggested LED system uses infrared sensors and ambient illuminance to measure environmental data such as the distance between the plant and the light source. The relationship between the data and the LED PPFD is then transformed, and ideal pulse width (PWM) is generated to substantially control the data and the LED PPFD (Ahn et al., 2017).

Cylindrical lighting system

The lighting system illustrated in Fig. 4 (c) was conceived and installed by the University of Southern California. Panels for growth are no longer horizontal. The panels are made to grow cylindrical plants. The cylindrical culture panels have a tank full of culture medium and are driven by gears. The cylindrical culture plate is rotated at a specific speed so that the culture medium may absorb all of the nutrient solutions and the LED can be used as a 360-degree light source, resulting in consistent illumination of the produced plants (Zhang et al., 2015).

Intelligent control of LED illumination

Light control is important to ensure effective growth, sustained development, and maximized crop productivity of plants in plant factories. An indoor lighting control (Bai and Ku, 2008; Matta and Mahmud, 2010) have implemented artificial intelligence in control systems. Nevertheless, this system requires composite mechanical systems that are difficult to implement. Currently, intelligent industrial light control uses a simple control mode based on traditional light sources; the LED light source is only used by a few systems, and the source LED light has a set wavelength and light intensity. Precision artificial lighting system, a recent development in intelligent machine vision, allows us to manage the light condition based on the needs of the plant. Setting up a wireless intelligent control system for a plant factory to assist with lighting control.

In several previous studies (Li et al., 2011; Sugiyama et al., 2007), fuzzy logic was chosen as an artificial intelligence control method for indoor lighting which demonstrated that fuzzy logic control systems are more reliable compared to ON-OFF control or PID control (Matta and Mahmud, 2010). Chen Y (Chen et al., 2009) found that adopting a double loop improved the efficiency of fuzzy logic control while increasing the control system's complexity. The symbolic logic system is simplified by using a single control loop. Furthermore, the use of a single control loop allows implementations to achieve accuracy levels of fewer than 2% standard errors. The illuminance of LEDs lamps is adjusted taking into account the illuminance of external lighting (Shafer et al., 2012). A control system model typically be made up of five components: LED lamp, driver, light sensor, controller, and transceiver (Shafer et al., 2012). Fig. represents the working of a smart LED lighting system with a fuzzy logic controller (Odiyur et al., 2021).

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Fig. 5. The working of a smart LED lighting system with a fuzzy logic controller (Odiyur et al, 2021)

Algorithm of LED intelligent control

Master controllers and slave controllers are the two types of controllers commonly utilized in this arrangement. The slave controller detects the power of the candle using the light sensor and transmits the measurement result to the controller, whereas the master controller's major role is to perform the symbolic logic control to regulate the homogeneity of the sunlight intensity. The master controller analyzes the data and changes the LED bulb illumination using a pulse width modulation (PWM) LED driver presented in Fig. 6.

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Fig. 6. Membership functions of fuzzy input (Matta and Mahmud, 2010)

In this model, communication between master and slave is via the recommended standard 485 (RS485) managed by the communication network (Shafer et al., 2012). The RS485 communication system allows the communication of multiple transceivers over a bus. This topology allows each slave controller to accept requests from the master controller and continuously transmit data to the master controller.

The system algorithm running on the master controller is shown in Fig. 7. The master controller continuously receives information about illuminance from the light sensor array. Each piece of information received is processed separately in a fuzzy logic control system. This process includes five steps: preprocessing, fuzzing, inference, defuzzification, and post-processing.

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Fig. 7. Algorithm of Control System (Shafer et al, 2012).

The fuzzy logic control system increases the PWM duty cycle when the actual luminance is lower than the expected luminance (setpoint). This means that the LED’s light is at its brightest when the candle's actual wattage is less than the point. Otherwise, if the actual second power exceeds the point, the PWM duty cycle will be reduced. This will dim the LED's light.

Conclusions

In-plant cultivation, LED is combined with artificial intelligence can change the point of light consistent with the evolutionary state of the plant, with the benefit of saving energy. Blue light is advantageous for chloroplast improvement and can increase the amount of chlorophyll in algal cells. Red light is the best light source to keep short-lived plants from blooming and sometimes helps plants bloom in dark times when distant red light can counter the effects of red light. The review demonstrated that fuzzy logic control systems are more reliable compared to ON-OFF control or PID control. Furthermore, the additional light angle shift has the benefit of providing enough light for the plant to grow and thrive. The goal of a fuzzy logic control system for controlling the luminous intensity homogeneity of light-emitting diodes (LEDs) is to overcome the problem of LED luminous intensity heterogeneity caused by small radiation angles. An array of light sensors in the control system continuously measure the light intensity. The control system changes the LED lighting based on the measurement results by adjusting the duty cycle of pulse width modulation (PWM). It is possible to establish light intensity homogeneity in the room using this model of the fuzzy logic control system.

Acknowledgement

This work was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, and Forestry (IPET) through the Agriculture, Food and Rural Affairs Convergence Technologies Program for Educating Creative Global Leaders, funded by the Ministry of Agriculture, Food and Rural Affairs (MAFRA) (Project No. 320001-4), Republic of Korea.

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