## 2 Materials and Methods  
### Materials  
For this study, basil (_Ocimum Basilicum_) seeds belonging to the variety called \"Genovese\" (Producer: Magnani Sementi) were employed as reference. In the first part of the experimental procedure, related to soils with a negligible quantity of fertilizers, three substrates were considered: Irish peat (Vigorplant Italia S.r.l., Fombio, Italy), Vegetal soil (Dal Zotto S.r.l., Fombio, Italy), and Organic potting soil for aromatic plants (OBI Smart Technologies GmbH, Wermelskirchen, Germany). In the second part of the study, with the aim of considering the fertilizer effect, a soil with considerable quantity of fertilizers was considered: Floradur B pot coarse universal potting soil (Floragard Vertriebs GmbH, Oldenburg, Germany). Detailed specifications of these substrates are reported in Table 1.  
With the aim to evaluate the combined effect of a very specific type of controlled release fertilizer and different light sources, in the second part of this study, a NPK lightweight aggregate from agro-residues, wastes, and by-products resulted from previous research [27; 28] was employed and compared with the employment of only soil enriched in fertilizers (Floradur B). According to the literature, the NPK controlled-release fertilizer demonstrated a relevant content of nutrients such as nitrogen (8%), potassium (8%), and phosphorous (5%) [27]. As an alternative to daylight, different LED modules specifically designed for horticulture applications were used. All the considered modules (from Intelligent Led Solutions, [30]) are equipped with 12 Oslon(r)SSL ThinGan LEDs (UX:3) and driven by a constant 370 mA current driver. The modules exploit a specific lens from LEDLi [31] to reduce the radiation angle of the LEDs from the original 80 deg to about 30 deg to obtain a more constant irradiation for all the plants. The considered modules use hyper red (HR) and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Property** & **Irish Peat** & **Vegetal Soil** & **Organic Soil** & **Floradur B** \\ \hline Apparent density (kg/m\({}^{3}\)) & 200 & 300 & 320 & 120 \\ (fresh matter) & & & & \\ Electrical conductivity & & & & \\ (mS/cm) & 0.0058 & 0.0053 & 0.0062 & 0.3800 \\ pH & 3.5 & 6.5 & 6.8 & 6.1 \\ Salt content (kg/m\({}^{3}\)) & - & - & 1.5 & 1.2 \\ N (kg/m\({}^{3}\)) & 0.70 & - & 0.05–0.30 & 0.21 \\ P\({}_{2}\)O\({}_{5}\) (kg/m\({}^{3}\)) & - & - & 0.08–0.30 & 0.12 \\ K\({}_{2}\)O (kg/m\({}^{3}\)) & - & - & 0.08–0.40 & 0.26 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Substrates properties as indicated by the different manufacturers. deep blue (DB) LEDs with 660 nm and 451 nm wavelength at the emission peak, and full width at half maximum (FWHM) values of 25 nm and 20 nm, respectively [32; 33]. Three different light recipes have been obtained exploiting modules with different ratios in terms of number of LEDs per type; see Table 2.  
All the three considered LED modules have been experimentally characterized by means of a low-cost spectral sensor (AS7341 from Ams, [34]) to obtain a qualitative comparison of the light spectrums provided. The results are shown in Figure 1.  
More in detail, the used sensor has a sensing element comprised of a matrix of photodiodes used in combination with embedded selective filters to obtain an 11-channel spectrometer. The filters are embedded using nano-optic deposited interference filter technology, and its package provides a built-in aperture to control the light entering the sensor array. Eight of the 11 available channels are reserved to the visible spectrum with filters centered at wavelengths of 415, 445, 480, 515, 555, 590, 630, and 680 nm, respectively. In addition, it has an optical channel dedicated to measure near-infrared light (NIR), an optical channel with a photodiode without filter (called \"clear\"), and a dedicated channel to detect 50 or 60 Hz ambient light flicker.