Measuring and evaluating solar radiative properties of plastic shading nets

Plastic shading nets are being used extensively in hot and sunny regions to protect plants from intense solar radiation. Different varieties of these nets are commercially available. However, the choice of net to fulfill specific shading requirements often depends on empirical or economic criteria and not on scientific considerations because essential information used to characterize the different types of nets is not available.In order to replace expensive measuring facilities that use artificial lighting to investigate the radiative properties of plastic shading nets, a simple method was presented to investigate these properties under global, diffuse and direct beam solar radiation conditions. Measurements were performed on clear sunny days, (December 28, 2008-February 10, 2009). Nets with colors and shading factors that are most commonly used in hot regions were selected for the study. The results showed that the behaviors of the plastic nets under solar radiation conditions were similar to those of translucent materials. Accordingly, it is possible to (i) treat plastic nets as translucent materials and (ii) investigate the equivalent optical constants (i.e., refractive indexes and extinction coefficients) for plastic nets as functions of the net solidity, texture type and color. Solidity and color of the net had significant effects on the radiative properties and the effect of color was much more than the effect of solidity. The shading factor of a plastic net, is a function of the daytime, depends on several design and meteorological parameters, so it cannot be used to describe a net. However, the net solidity together with color, and the daily integrals of the shading factor and of the radiative properties are appropriate parameters for describing a net.