## 1 Introduction  
Research is being carried out on the use of modern technologies for agriculture, and advances are being made in this field [1]. Vapor pressure deficit (VPD) has been identified as an increasingly important driver of plant functioning [2], because VPD affects plant transpiration rates, which are closely related to the water condition of a plant. If the VPD is high, meaning high transpiration, it pulls water that contains the nutrients required for plants. This would cause plant metabolism to accelerate, furthering development. If the VPD is low, the opposite occurs. Thus, VPD regulation has been widely recognized as having the potential to improve plant growth and productivity. \[\text{SVP}=0.6108\,\exp\biggl{(}\frac{17.27\text{T}}{\text{T}+237.3}\biggr{)} \tag{1}\]  
VPD is the difference, i.e., the deficit, between the amount of moisture in the air and how much moisture the air can hold when it is saturated. The atmosphere can hold only a certain amount of water vapor at a specific temperature, and the maximum amount of water vapor that can be held at a specific temperature is called the saturation vapor pressure (SVP). The SVP is determined by the air temperature (T). The value of the SVP at air temperature can be calculated by Equation (1). When the temperature of the atmosphere increases, the SVP increases, and when the temperature decreases, the SVP decreases. Because it increases or decreases non-linearly, the mean SVP at the mean daily maximum and minimum air temperatures is used for a given period. The actual amount of water vapor held at the current temperature is calledthe active vapor pressure (AVP). The value of the AVP for a given relative humidity (RH) is determined by Equation (2) [3]. \[\text{AVP}=\text{SVP}\frac{\text{RH}}{100} \tag{2}\]  
The VPD can be obtained simply using the SVP and AVP with Equation (3). \[\text{VPD}=\text{SVP}-\text{AVP} \tag{3}\]  
[PERSON] [4] reported that most plants grow well at a VPD between 0.5 and 0.8 kPa (kilopascals). According to the guidance offered by [5], the optimum range of VPD for plants is around 0.5 to 1.2 kPa. However, the recommended levels of VPD differ from the growth stages of a plant [6]. For example, research recommends 0.8 kPa as an ideal VPD for clones, around 1.0 kPa for the vegetative stage, and around 1.2 to 1.5 kPa for the flower stage. A very high VPD of 2.2 kPa could cause plant stress and fruit cracking in tomato crops [7]. Studies on VPD have empirically observed the impacts of a high or low VPD on the physiological responses of plants [4; 8; 9; 10]. There is an uncertainty associated with VPD impacts on crops because of the difficulty in disentangling VPD effects from other climate parameters such as radiation, temperature, and atmospheric CO\({}_{2}\) concentrations [11]. For example, responses of stomatal conductance to high-VPD conditions generally follow an exponential decrease [12]. However, a high VPD accompanies high radiation, and the leaf-level stomatal conductance of individual plants is sensitive to variation in radiation and temperature [13]. This makes it difficult to untangle their relative effects on crops. While some effects may be explained by a high VPD, others may be partially explained by high radiation. High humidity, i.e., a low VPD, reduces transpiration, growth, and photosynthesis [11]. However, because the water retention on the leaf surface can impair stomatal functioning, not all effects can be explained with a reduced VPD [14]. Therefore, these recommendations can be coordinated in accordance with diverse species and environmental factors under the careful observation of crop growth. The VPD can be adjusted through temperature, humidity, and light intensity. Modern technologies have been used for regulating the VPD [15; 16; 17]. Increasing temperature, decreasing humidity, and increasing light intensity increase the VPD, while vice versa, they decrease the VPD.