Modelling of radiative PAR transfer in a tunnel greenhouse

The modelling of radiative photosynthetically active radiation (PAR) transfer is required to enable light distribution in greenhouses to be determined. Thus, study tests, the accuracy of a well-known radiation model for plastic tunnel greenhouses. The radiation was measured inside and outside a single plastic-covered tunnel greenhouse and compared with calculations performed with the model suggested by Rosa et al. (Rosa model). The average transmissivity was around 80% on cloudy days and 78% on sunny days. Model calculations were 7% lower on cloudy days and 24 +/- 12% higher than measurements on sunny days, which shows that more complex models taking account of shadows cast by the frame and changes in transmission resulting from condensation and dust have to be used. Additionally, the accuracy should also be improved by using a more accurate physical model that allows for diffuse and direct irradiance, reflection, transmission, scattering and shading. (C) 2001 IMACS. Published by Elsevier Science B.V. All rights reserved.