EFFECT OF COVERING MATERIAL AND SHADING ON INTERIOR LIGHT INTENSITY IN POLY-GREENHOUSES

Abstract

The objective of this research was to examine the influence of two different poly-greenhouse covering material types and their properties on the interior light intensity to choose the proper one for covering under Fayoum depression climatic conditions. Measurements of global solar radiation (GSR) and light intensity were made inside and outside six poly-greenhouse-covered prototype structures (Quonset-style). Each prototype structure was 1.0 m length, 1.0 m width and 0.8 m height. Two small doors in the narrow sides of each prototype were kept open during the day-light for natural ventilation. Results showed that the average transmittance in GSR of both new white polyethylene films and new black screen shade net sheets were 74.05% and 55.45%, respectively. Exposure the poly-greenhouse cover to the climatic conditions reduced its transmittance to global solar radiation (GSR). The relative losses of GSR transmittance were 13.96 % and 17.64 % for both old-cleaned and old-dirty polyethylene films, respectively, as compared with the new polyethylene film (74.05%). The average losses of GSR transmittance were 12.93% and 19.42% for both old-cleaned and old-dirty black screen shade net, respectively, as compared with the new black screen shade net cover (55.45%). The new white polyethylene films and new black screen shade net sheets reduced the interior light intensity of the prototypes by an average of 18.3% and 68.4% as compared with the average exterior light intensity, respectively. In addition, old-cleaned and old-dirty polyethylene films reduced the interior light intensity by an average of 20.8% and 34.8% as compared with the identical new white polyethylene film, respectively. While, old-cleaned and old-dirty black screen shade net reduced the interior light intensity by an average of 27.3% and 39.9 % as compared with the identical new black screen shade net, respectively.