Geoola, F., Institute of Agricultural Engineering, ARO, The Volcani Center, PO Box 6, Bet Dagan, 50250, Israel
Peiper, U.M., Institute of Agricultural Engineering, ARO, The Volcani Center, PO Box 6, Bet Dagan, 50250, Israel

A round arch greenhouse for the investigation of optical transmission and ageing of agricultural plastic films in general, and of anti-drop (anti-fog) films in particular, was designed and constructed. The experimental greenhouse, which consisted of eight identical sections could be covered with different types of plastic films for investigation of solar radiation transmission and amount of condensed run-off water. Comparison of light transmissions of the films, over a period of 3 months showed that in a dry state, all films had higher transmissions than in a wet state. Transmissions of anti-drop films were found to be close to their dry state values and to be higher than those of ordinary films. During the period of the experiment, the respective daily normalized amount of condensed run-off water collected did not vary significantly. The amount of run-off water collected was higher for anti-drop films. It was observed that the deterioration of the surface active agents of anti-drop films was affected strongly by the amount of water that flows on their surface. In the course of ventilation of the greenhouse, it was observed that the required drying time for an anti-drop film was almost five times less than that of a conventional plastic film. The loss of transparency of plastic films due to dirt during the period of experiment was between 9 and 10%.