Abstract: For determining the optical performance of greenhouse covering materials other than standard float glass the current Dutch NEN 2675 norm is no longer appropriate. The emergence of a new generation of materials (diffuse, layered) resulted in a new measuring protocol developed by TNO and Wageningen UR. In line with this protocol Wageningen UR has developed an accurate measuring device (Transvision) for measuring the light transmittance for direct and hemispherical incident light. The device is based on spectral analysis of a perpendicular beam passing the material under a variable angle of incidence into an integrating sphere. With the angular transmission data, the hemispherical transmission can be calculated which is the most important benchmark for the performance as a covering material at northern latitudes. The device is specially developed for measuring thick, multi-layer and large materials which cannot be cut for testing, like tempered or structured glass panes. For clear float glass the device meets the specifications of the NEN 2675 and the results are comparable with those of professional spectrometer systems.
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