## 1 Introduction  
In recent years, the interest toward the applicability of light-emitting diode (LED) lights for indoor cultivation has significantly grown, with the aim of creating a more affordable and ecological production for plants compared to fluorescent lighting and high-pressure sodium (HPS) lamps [1, 2]. In fact, artificial light supply presents additional costs compared to cultivation under natural daylight due to energy demand, but it is mandatory in an indoor environment and wherever natural light is not sufficient. For example, these systems are necessary at northern latitudes, where a strong variation of daylight is observed during the year, to address the current challenges that the greenhouse industry is facing (i.e., energy, environment, and market) [3]. Moreover, it is beneficial to increase the product yield and quality of the final product because growing plants in controlled environment allows drastically reducing the use of pesticides. Finally, controlled-environment agriculture is a key subject of the worldwide food optimization system, due to the upcoming population growth and climate changes scenarios [4]. In this context, LED lights are expected to replace conventional light sources due to their longer functional life, lower operating temperatures, and lower energy consumption, thereafter decreasing the operational costs of indoor urban farming. In addition, compared with conventional light sources, LED technology offers an easier and cheap way for light spectrum manipulation, and this is beneficial for crop growth regulation [5; 6]. Indeed, LED lights provide tunable wavelengths to be matched to plant photoreceptors, including phytochrome and cryptochrome, in order to have optimal plant growth in terms of morphology (e.g., height, leaf area, thickness, and stem length) and quality (e.g., metabolites) [7; 8; 9; 10; 11]. Therefore, this provides a new opportunity to manipulate the quality and quantity of vegetable products for markets and meet the demands of retailers in a future perspective involving artificial intelligence control over a real-time autonomous horticultural system [12]. Artificial intelligence techniques ensure minimal human manipulation by defining very tailored target parameters, ensuring an increased efficiency of the system from the environmental and economic point of view. This vision seeks the full digital control of the light quantity, in order to optimize the crop productivity, which may contribute to an optimized production of food [3; 13]. For example, it could be possible not only to control artificial light based on specific natural light conditions but to account for potential physiological changes in the crop [13]. As a result, research is strongly focusing on the application of different LED lights on different plants, and several types of LED-based lamps became available for commercial plant production [14]. Taking into account the more recent research on this topic, generally, blue light is necessary for the morphologically healthy growth of plants mainly involving a transpiration mechanism and stem elongation [15; 16; 17]. In contrast, red light plays a major role in plant photosynthesis [18; 19]. In fact, it has been demonstrated that plants' chlorophyll A and B efficiently absorb blue and red lights wavelengths, respectively [20]. It has been confirmed that the optimal ratio between blue and red light is of great relevance in determining plant yield, as it has a strong effect on the conversion efficiency of natural photosynthesis, which is peculiar for each vegetable [12; 21]. In addition, research on this topic is generally conducted using commercial available light that is not varied during the experimental procedure, and principal results indicate that the complexity of the plant physiology requires a multi-objective optimization approach [12].