|Authors: ||E.S. Runkle, P. Jaster, R.D. Heins, C. Thill|
|Keywords: ||far-red light, light quality, photoselective film, solar radiation, shade curtain|
Many greenhouse growers use metalized shading fabrics to reduce temperature, but these fabrics also reduce photosynthetic active radiation (PAR, 400 to 700 nm), which can potentially reduce crop quality and yield.
Recently, a multilayered film was developed that reflects a significant portion of near infra-red radiation (NIR, 700 to 1100 nm) i.e., heat, with minimal PAR reduction.
We quantified the photothermal environment under two prototypes of the NIR film (as a solid screen and a woven curtain) and a neutral density (N) metalized shading fabric in a commercial greenhouse located in a subtropical (lat. 28.7 oN) climate.
Light transmission through the greenhouse glazing, structure, and shading materials was measured on a cloudless day when the screens were constantly deployed.
Compared with that outdoors, the N curtain, NIR curtain, and NIR screen transmitted 20.7%, 41.1%, and 43.2% PAR (on a quantum basis) and 20.5%, 33.9%, and 35.6% short-wave radiation, respectively.
Therefore, on a photon to energy basis, the N curtain transmitted an average of 2.31 μmol·m-2·s-1 PAR per Wμm-2 of short-wave energy (or μmol·W-1·μs-1) and the NIR curtain and screen transmitted 2.78 μmol·W-1·s-1. The NIR materials reflected a significant portion of energy from 750 to 1100, and was maximal when the sun altitude was 65o. Although PAR values were approximately 100% greater under the NIR films, the average air temperature at the outlet (fan) end of the greenhouse was within 0.8 oC under the three filters.
Therefore, this multilayered NIR film provides an alternative to metalized shading fabrics because it transmits more PAR per unit total radiant energy.
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