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Typical greenhouse covering materials used in the majority of low- and mid-tech greenhouses are polyethylene-based plastic films, and in most high-tech greenhouses, glass is used.
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The greenhouse covering material determines the intensity and spectrum of the sunlight entering the greenhouse - alongside the crop growth and production, this also affects the greenhouse microclimate and hence, the energy use. The spectrum of sunlight ranges from wavelengths of 300 - 2500 nm - including UV (300 - 400 nm), photosynthetically active radiation, or PAR (400 - 700 nm), and near infrared radiation, or NIR (700 - 2500 nm). The PAR component governs photosynthesis and crop growth, while the NIR component provides free heat energy for the greenhouse.
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