## 4 Discussion  
### Radiometric Properties  
Related to the radiometric properties, the behavior of the absorbance was inversely proportional to the transmittance and reflectance [5]. The behavior of the transmittance of the blue EPC was similar to that described by [PERSON] et al. [39]. The grey, yellow and colorless EPCs presented a low transmittance in the UV region due to their photod stabilizer additives. The behavior of the yellow EPC was due to the use of nickel quencher photod stabilizer additives, which, by absorbing UV radiation and preventing degradation, also absorbed part of the PAR band [9]. The use of HALS-type photostabilizers in the grey and colorless EPCs was more efficient when it comes to the starting transmission in the PAR region compared to using the nickel-quencher-type additive [11] because they allowed a higher percentage of radiation to pass through. A low transmission of UV-A radiation can help to control insects, although it can also influence the behavior of bees and bumblebees in the same way [22; 40]. [PERSON] [41] mentions that an anti-insect plastic cover must be able to block between 80% and 100% of UV radiation, and that the additives used must not influence its photoselective qualities throughout its useful life. The lowest PAR radiation transmission was presented by the blue EPC. [PERSON] et al. [42] reported how a blue shading mesh transmitted 46.5% of the incident PAR, and the blue EPC presented a value of 32.04% in this study. This difference may be due to the fact that a mesh is porous while plastic is not, in addition to other factors such as the thickness and the quantity and quality of the additives. Regarding the greater PAR transmission by the yellow EPC compared to the colorless EPC, this may be due to the fact that the latter had a greater thickness in addition to the nature of the photod stabilizers [9; 43]. A low transmission of PAR radiation has a direct impact on crops according to different studies carried out in greenhouses by [PERSON] et al. [44], which show that a low incidence of PAR on tomato crops (_Solanum lycopeneum_) produces a clear reduction in productive yields. [PERSON] et al. [45] demonstrated that both in tomato and cucumber (_Cucumis sativus_), there is less CO\({}_{2}\) assimilation when the level of PAR radiation is lower. Although it is certain that the photosynthesis rate increases as the amount of PAR radiation increases and vice versa, whether this occurs to a greater or lesser extent will depend on each crop [46]. Nevertheless, it should be considered that the blue EPC presented high transmissivity values in the blue and red spectral regions, in which the efficiency of the use of spectral energy by plant pigments (chlorophyll a and b and carotenoids) generates high rates of bioassimilates and therefore higher yields [47]. Figure 9: Average horary relative humidity recorded inside each greenhouse and outside for (**a**) September, (**b**) October and (**c**) November. As the PAR and NIR spectra are consecutive, when trying to reduce the latter, it is possible to also avoid reducing the former [48]. In this sense, [PERSON] et al. [49] suggest that covers with additives that reflect NIR radiation, in order to be considered anti-thermal, must provide a high transmission of PAR radiation and a high reflection of NIR radiation. Other authors, such as [PERSON] et al. [50], mention that anti-thermal films must present transmissions of less than 25% in terms of NIR. As regards the transmission of NIR radiation, the blue EPC showed heterogeneous behavior throughout the spectrum due to its blue coloration, which was similar to a test carried out by [PERSON] et al. [39], where a blue cellophane sheet showed the same pattern, although at lower percentages, as it was less thick. The grey EPC yielded very similar values to the blue EPC (Table 1), although, in this case, the behavior pattern was highly homogeneous throughout the entire band.