Standardized measurement of hemispherical light transmission in greenhouse covering materials

Ayrox has noted that their clients have been asking for more precise light transmission measurements in greenhouse panels.

Indeed, the previous commercially available instruments only measured the perpendicular light transmission. However, to better mimic real solar radiation, which seldom happens vertically, at least in Continental Europe, the recently updated NEN 2675-2018 standard requires that light transmission measurement should be done from different angles of incidence, just like the movement of the sun.

Together with Admesy, Ayrox proposes a device and a measurement service according to the new requirements of the NEN 2675-2018: the Hemispherical Light Transmission meter (H-LT meter).

"It not only meets the requirements of this standard but surpasses them. Indeed, high levels of accuracy are key. For crops such as tomatoes, for example, 1% extra light brings approximately 0.7 - 1% extra production, so growers require a measurement device that can be accurate to a 10th of a percentage, which is why the manufacturer, Admesy, ensured that their device complies with this level of accuracy," the Ayrox team explains.

Until now, this kind of device was mainly accessible for research purposes via Wageningen University & Research (WUR). As a result, a standardized hemispherical light transmission measurement tool for broad commercial distribution was not available. The H-LT meter fills this need by providing glass processors, greenhouse engineers, and growers with an easy-to-use solution that enables precise measurement of hemispherical light transmission and scattering in greenhouse horticulture. Since a particular range of light wavelengths can be more suitable for specific crops, the H-LT meter is adapted to measure both clear and diffuse panels.

The H-LT meter features a suspended gonio system surrounded by an enclosure made from high-end item profiles and panels blocking external light and shielding the user from moving parts, thus ensuring user safety. With the ability to take measurements at various angles between 0° and 70° (every 5°), this device provides comprehensive data for analysis. Moreover, its broad wavelength range of 250nm to 1100nm, dependent on the emission spectrum of the light source, ensures accurate evaluation across the entire spectrum of interest. The system allows to measure automatically 50x50cm samples made of either glass or other materials; manually, the enclosure is fit for bigger samples as well.

To validate the device's reliability, an interlaboratory comparison with WUR Business Unit Greenhouse Horticulture was conducted on clear and diffuse samples. Both are within the requirement of 1% of the norm. The spread in results is proven to not exceed ±1% point for hemispherical transmittance.

"The H-LT meter is a cutting-edge tool that addresses the critical need for accurate hemispherical light transmission measurement because the amount of light directly impacts crop growth and yields."

For more information:
Av. de Fré 98 bte 7 - B-1180 Bruxelles
Tel.: +32 (0) 2 375 61 98

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