Effect of Aging on the Spectral Radiative Properties of Plastic Film-Covered Greenhouse under Arid Conditions

Plastic films are widely used to cover greenhouses in arid regions. Unlike predicting the total radiative properties of films, predicting the deterioration behavior of the spectral radiative properties is quite difficult during the service life of the films. These properties should be of great interest for crop morphogenesis studies. This study was to investigate the degradation behavior of spectral transmittance, \( \tau_{\lambda } \), and reflectance, \( \rho_{\lambda } \) (in the solar spectrum range), of a 200 µm thick, LDPE film-covered greenhouse model that was exposed for 1 year to an arid climate. Every 30 days, \( \tau_{\lambda } \) and \( \rho_{\lambda } \) were measured for six samples taken from the six surfaces of the greenhouse cover and averaged to obtain the cover properties. Based on the collected data, nonlinear correlations (each as a function of the wavelength, λ, and the exposure time, t) were obtained to predict \( \tau_{\lambda } \) and \( \rho_{\lambda } \) at any time during the service life of the cover under such climatic conditions. Results showed that 1 year exposure drastically reduced the spectral and total transmittance of the cover film to global and PAR solar radiation by about 32 % and increased the spectral and total reflectance by about 19 % compared to new film. Degradation of the radiative properties of the film did not affect the light quality or the transmission ratios of light into the greenhouse. The transmitted PAR was reduced from 115 W·m−2 to 27 W·m−2 after 1 year exposure.