## 3 Results and Discussion
One of the main limiting factors in the expansion of VF concerning the use of traditional artificial light sources (e.g., HPS lamps) is that they have high costs, high energy consumption, limited lifetime and, more importantly, a fixed light spectrum (e.g., HPS lamps). All these limits are overcome by using LEDs. First, LEDs allow the obtaining of fully customizable light recipes in terms of an adjustable light spectrum and irradiance depending on both the type of plant we want to grow and the specific phase of the growth cycle. Second, they have a power consumption that is at least 50% lower than HPS lamps for a given irradiance and a lifetime that is at least three times higher with a cost that has been constantly decreasing in recent years with a confirmed trend for the next year. Of course, less power consumption to guarantee a given level of irradiance means less need for energy and, consequently, using LEDs in VF has a significant benefit in terms of sustainability and CO\({}_{2}\) footprint. Moreover, VF with LEDs allows the increase of the product yield per square meter of soil because it allows the exploitation of multi-plant systems. The lower space needed for the VF system also allows it to be placed in urban scenarios with lower costs. The placement of big VFs close to (or even in) urban centers means that logistics costs are also drastically reduced and, once again, this is beneficial for the environment because both the number and operation time of vehicles producing high emissions (in primis, tractors and trucks) are reduced. In addition, reduced logistics costs theoretically allow a lower final price for the product paid by the consumer. Regarding nutrient delivery and irrigation systems, the use of a substrate culture system based on perlite and peat, coupled with the slow-release fertilizers, solves the problem of nutrients delivery, leaving only the need for irrigation. The use of irrigation systems in VF allows for water consumption that is almost 10% of that of open field agriculture REF. A further benefit of this system is that no pest control systems are needed, and no pest problems were noticed during the growth experiments performedin this study. Greater VF systems will probably need some pest monitoring systems but the use of pesticides is usually near to zero. Regarding climate control systems, the reduction of volume required for the growth of every lettuce plant when using LED instead of HPS lamps reduces the total volume of space that needs to be air conditioned. One of the main drawbacks of this system is that it was optimized only with lettuce, while every crop needs specific tailored light conditions and nutrients supply. Other drawbacks include the greater amount of energy needed by VF systems with respect to traditional farming methods, e.g., open field or greenhouse farming. The economic profitability of this system depends on many factors. Among them are the price of energy and the market demand for the specific crop. VF systems require a higher initial economic investment, but they have been demonstrated to be more profitable compared to systems based on HPS lamps after a limited number of years [15]. The environmental sustainability of a VF system also lies in the energy mix at the base of the energy used, as demonstrated by [57].