Experimental transmittance of polyethylene films in the solar and infrared wavelengths

The growing use of plastic film coverings in agriculture is due to the possibility of increasing the air temperature around the plants, reducing radiative and convective energy losses, protecting fruit trees from adverse weather conditions, reducing fungal diseases, assuring less reliance on herbicides and pesticides, better protection of food products and more efficient water conservation. Low-density polyethylene (LD-PE) is one of the most widely used plastic films for greenhouse coverings, low and medium tunnels and soil mulching. In this paper, we present radiometric properties of a new and old (used for more than five years) LD-PE film, experimentally investigated using different methodological approaches for different wavelength bands, especially at medium IR. Experimental measurements in the IR wavelength spectrum, included the Near (0.78-3 μm), i.e. N-IR-A (0.78-1.4 μm) and N-IR-B (1.4-3 μm) and Medium (3-50 μm) in accordance with ISO 20473 (E) 2007 were carried out. Experimental results obtained are in agreement with those in the literature and show that the aging effects are minimal in the plastic film used for five years. This finding is crucial for greenhouse design. Referring to practical applications, energy balance of an ordinary agricultural greenhouse was also evaluated. The authors believe that this research results on all the optical properties in a wide spectral range of LD-PE will be useful not only in agriculture, but also for any other solar engineering application.