DIRECT AND DIFFUSE LIGHT TRANSMISSION OF INSECT-PROOF SCREENS AND PLASTIC FILMS FOR CLADDING GREENHOUSES

ISHS Acta Horticulturae 559: V International Symposium on Protected Cultivation in Mild Winter Climates: Current Trends for Suistainable Technologies

DIRECT AND DIFFUSE LIGHT TRANSMISSION OF INSECT-PROOF SCREENS AND PLASTIC FILMS FOR CLADDING GREENHOUSES

Authors:	J.I. Montero, A. Antón, J. Hernández, N. Castilla
Keywords:	Optical properties, ageing, dirt, dust, thermal polyethylene, three-layer film
Abstract: Optical properties of several greenhouse-cladding materials were evaluated using direct and diffuse light transmission laboratory equipment. Samples of two insect-proof screens of different porosity, four low density polyethylene (PE) films and one co-extruded three-layer film were evaluated. The effect of ageing on direct light transmission of some of the tested materials was also measured. Main results can be summarised as follows: The capability of insect-proof screens to transmit light was very good and comparable to that of the three-layer films. Light transmission is a function of the porosity of the screen; the bigger porosity the better light transmission. Three-layer film and 0.1 mm PE non-thermal films transmitted more light than the other plastic films. Maximum light transmission for these materials was close to 90 %. Light transmission of thermal PE films is clearly less than that of three-layer films. For instance, maximum direct light transmission of one of the thermal PE samples was only 83 %. This loss in light is expected to cause a reduction in yield and quality of winter crops in Mediterranean areas. Film ageing under exposure to field conditions contributed to a loss in light of 5 % approximately. For all tested materials, diffuse light transmission was lower than direct transmission at zero incidence angles. Diffuse light transmission ranged from 81 % for the most porous screen to 65 % for one of the thermal PE samples.
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