## 3 Results  
### Radiometric Properties  
Figure 2 shows the percentage of the transmittance, reflectance and absorbance for each of the films assessed (blue, grey, yellow and colorless EPCs). Table 1 shows the average percentage values of the transmittance in the UV-A, PAR and NIR spectral regions of the polymers studied. Table 2 shows the average percentage values of the transmittance in the blue, red and far-red spectral regions of the polymers studied, and Table 3 shows the average percentage values of the ratios between the transmittance of the PAR/NIR, R/FR and B/R regions of the polymers studied. The patterns of the grey, yellow and colorless EPCs were similar for the reflectance, transmittance and absorbance. It is necessary to note that the anti-thermic additive used in the grey EPC affected all the spectral regions equally. The external transmittance of the yellow EPC increased linearly from 400 nm to 450 nm, while the absorbance decreased proportionally to this, until reaching 500 nm, at which point they behaved uniformly throughout the entire spectrum shown. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Spectral Region (nm)**} \\ \cline{2-4} EPC & **UV-A** & **PAR** & **NIR** \\  & **(350–400)** & **(400–700)** & **(700–1100)** \\ \hline Blue & 9.45 & 32.04 & 61.45 \\ Grey & 36.85 & 62.33 & 62.83 \\ Yellow & 38.64 & 92.34 & 94.55 \\ Colorless & 28.11 & 85.77 & 86.93 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Average percentage values of transmittance in the UV-A, PAR and NIR spectral regions of polymers studied. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Spectral Region (nm)**} \\ \cline{2-4} EPC & **Blue** & **Red** & **Far Red** \\  & **(400–500)** & **(600–700)** & **(700–800)** \\ \hline Blue & 42.20 & 24.66 & 44.06 \\ Grey & 61.84 & 62.61 & 62.34 \\ Yellow & 86.42 & 94.91 & 94.88 \\ Colorless & 84.26 & 86.63 & 86.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average percentage values of transmittance in the blue, red and far-red spectral regions of the polymers studied. Figure 2: Absorbance, transmittance and reflectance across the spectrum of the polymers studied. The colorless EPC produced a higher transmission throughout the spectrum than the yellow EPC. On the other hand, the colorless EPC did not reach transmission values as high as those of the yellow EPC. The PAR transmission in the blue EPC was 32.04%, in the grey EPC it was 62.33%, while in the colorless EPC and yellow EPC it was 85.77% and 92.34%, respectively. This characteristic of HALS-type photostabilizers can also be seen in the grey EPC, where the transmission pattern at the beginning of the PAR region was practically identical, although at lower percentages, due to the \"anti-thermal\" additive. The blue EPC also had these additives incorporated into it, but due to the added blue pigment, its behavior was somewhat distorted and not as obvious. The comparison between the films studied shows that the blue EPC presented the lowest transmissivity in all the spectral regions analyzed (Figure 2 and Table 1). The grey EPC was the one that attained the highest percentage of diffusion, which was probably due to the aluminized particles used in its composition to reflect NIR (Table 4). The diffusion percentage of the rest of the plastic films was due to the nature of the polymers and additives used. Figure 3 shows the relationship of the transmittance on both sides of each plastic film to study the symmetry of the film. The blue, grey and colorless EPCs presented a high symmetry in the transmittance between their sides. However, the yellow EPC demonstrated asymmetry between the sides, with the transmission of the external side being lower than that of the internal side from 300 nm to 500 nm, which represents a 9% transmittance. From 500 nm, it also showed a high symmetry. This aspect must be taken into account when installing the plastic film.