## 2 Materials and Methods  
### Experimental Growth Test  
Growth tests were performed in a controlled indoor environment using nine pots per test with a growing area of 50 cm\({}^{2}\) each. As growing substrate, Floradur B pot coarse universal potting soil was chosen, enabling the growth of basil without the need to add further nutrients (Producer: Floragard Vertriebs GmbH, Oldenburg, Germany). This substrate was already employed in a previous study, demonstrating that its main nutritional elements and physical properties are suitable for basil growth [30]. Five seeds of basil (_Ocinum basilicum_) of the \"Genovese\" variety (Producer: Magnani Sementi) were sowed in every pot (Figure 1a) and grown for 30 days at 19 \({}^{\circ}\)C and a relative humidity equal to 60% \(\pm\) 5%. Water was added once every two days to fulfill the constant humidity, and was recorded as a result. The used growth box was completely isolated from natural light. Artificial light was obtained using solely commercial LED modules specific for horticulture [31]. Each module comprised twelve OSRAM Oslon(r)SSL ThinGaN LEDs (UX:3). The modules had three different types of LEDs, i.e., Hyper Red (HR, wavelength = 660 nm, [32]), Deep Blue (DB, wavelength = 451 nm [33]), and Warm White (WW, color temperature = 3000 K, [34] arranged with different ratios of number of HR, DB and WW LEDs per module. This allowed to obtain a different light spectrum for each type of module. Table 1 summarizes the composition in terms of number of LEDs per type per module and corresponding Photosynthetic Photon Flux (PPF), obtained following the same procedure described in [26]. Accordingly, with the experimental plan explained in Section 2.2, all the light recipes tested were obtained using two modules each, i.e., 24 LEDs in total, in different combinations as summarized in Table 2, where the same notation used in Table 1 has been applied (e.g., 8 HR:10 DB:6 WW means 8 Hyper Red LEDs, 10 Deep Blue LEDs and 6 Warm White LEDs). The LEDs were arranged in different combinations to obtain different HR:DB ratios, and the presence or absence of white light, as shown in Table 3 and as described in Section 2.2. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Module** & **Total Number** & **Total Number of** & **Total Number of** & **Total Number of** & **Total Number of** \\
**Code 1** & **of LEDs** & **HR LEDs** & **DB LEDs** & **WW LEDs** & **Total PPF [\(\mu\)mol/s]** \\ \hline
5 HR:1 DB:6 WW & 12 & 5 & 1 & 6 & 21.17 \\
9 HR:3 DB & 12 & 9 & 3 & - & 24.91 \\
6 HR:6 DB & 12 & 6 & 6 & - & 25.66 \\
3 HR:9 DB & 12 & 3 & 6 & - & 26.40 \\ \hline \end{tabular}  
* Module’s coding: <# HR LEDs>HR: <# DB LEDs>DB: <# WW LEDs>WW.  
\end{table} 
Table 1: Composition of the LED modules used in the experiments to create the light recipes considered in the experimental plan. Figure 1: (**a**) Scheme of seedlings distribution in a single pot; (**b**) scheme of pots position under the same light conditions. A photoperiod of 16 h/day was chosen. Pots were placed at three different distances from LEDs, namely 60, 70, and 80 cm between the light source and the top of pots, corresponding to three different light intensities. Distances were kept constant during growth, elevating LED modules. Pots at the same level were swapped every two days, to correct for possible differences in light intensity due to the different illumination angles (Figure 1b). In the experimental setup, the LED modules had an emission cone angle of about 30 degrees obtained by means of ad-hoc optical lens [35], and had a fixed power supply (i.e., a constant light intensity). Therefore, the only way to obtain different light intensities was to change the distance between plants and light source. From a practical point of view this meant that the larger the distance, the smaller the PPF emitted by the LED modules that reached the plants because the difference between the illuminated area and growth area was larger.