## 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. As burying soil, Floradur B pot coarse universal potting soil (Floragard Vertriebs GmbH, Oldenburg, Germany) was employed. Detailed specifications about this substrate can be found in a previous study, as the same soil was employed to promote the comparison among different soils suitable for basil [28]. This soil respects the limits generally applied to fertilizer compounds necessary to be sold and employed [30]. The experiments were conducted by exploiting as artificial light commercial LED modules realized with OSRAM Oslon(r)SSL ThinGaN LEDs (UX:3) technology, [31]. The composition in terms of number and type of LEDs are summarized in Table 1. The modules were characterized using an Orb Optronix TEC-100 electrical-thermal-optical (ETO) system with integrating sphere. In horticulture, from an application point of view, the main parameter to consider for a light source is the photosynthetic photon flux (_PPF_). The overall photon flux (_PF_) in umol/s of a light source depends on the radiant flux (_RF_) in W, and is proportional to the light wavelength, \(\lambda\). Only the portion of photons with wavelengths in the range 400-700 nm (i.e., the so-called photosynthetic active region PAR) contributes to photosynthesis. _PPF_ is \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Module Type**} & \multirow{2}{*}{**Module Code 1**} & **Total Number** & **Total Number of** & **Total Number of** & **Total Number of** \\  & & **of LEDs** & **HR 1 LEDs** & **DB 2 LEDs** & **WW 3 LEDs** \\ \hline
1 & 5 HR:1 DB:6 WW & 12 & 5 & 1 & 6 \\
2 & 9 HR:3 DB & 12 & 9 & 3 & - \\
3 & 6 HR:6 DB & 12 & 6 & 6 & - \\
4 & 3 HR:9 DB & 12 & 3 & 6 & - \\ \hline \hline \end{tabular}  
* HR = hyper red. 2 DB = deep blue. 3 WW = warm white.  
\end{table} 
Table 1: Composition of the LEDs modules used in the experiments to realize the considered light combinations. the portion of \(PF\) due to photons within the PAR. Since the ETO system provided the data concerning the whole modules, the contribution of each LED type was calculated off-line. For the hyper red [32] and deep blue [33] LEDs, the \(PPF\) contribution of a single LED (i.e., \(PPF_{singleLED\_HR}\) and \(PPF_{singleLED\_DB}\)) were extracted from datasheets using (1) or (2) depending on the specific LED  
\[PPF_{singleLED\_HR}\approx PF=RF\cdot\lambda\cdot 0.00836/1000 \tag{1}\]  
\[PPF_{singleLED\_DB}\approx PF=RF\cdot\lambda\cdot 0.00836/1000 \tag{2}\]  
where, \(RF\) is the radiant flux in W, \(\lambda\) is the peak wavelength of the LED in nm, the light wavelength, the coefficient \(0.00836=1/(h\cdot c\cdot N)\)\(h\) is [PERSON]'s constant, \(c\) is the speed of light and \(N\) is the constant of Avogadro. \(RF\) and \(\lambda\) are reported in the datasheet. For a given monochromatic LED, the error derived by approximating PPF with PF is negligible because outside the PAR range there are no photons emitted. For warm white LEDs, instead, it is not possible to apply directly (1) or (2) due to the intrinsic nature of the white light. Different from single color light sources, white light sources have not a single dominant wavelength in the spectrum. For this reason, the datasheets of white LEDs usually do not report the \(RF\). They report instead the luminous flux (\(LF\), in lumen) for a given color temperature (i.e., 3000 K for the considered LEDs). In this case, to obtain the estimated \(PPF_{singleLED\_WW}\) contribution of the warm white LEDs a two-steps empiric procedure was used. First, the relative spectral emission of the considered white LEDs [34], reported in the datasheet was included in the freely available spreadsheet tool provided by lighting analysts [35]. This allowed to obtain a luminous-to-photon flux conversion factor \(K_{LF\text{-}to\_PF}=14.64\).