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Testing of Various Monochromatic LED Lights Used in Supplemental Irradiation of Lettuce in Modern Urban Rooftop Polytunnels

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Applied Engineering in Agriculture. 35(3): 439-452. (doi: 10.13031/aea.13192) @2019
Authors:   Chung-Liang Chang, Kuang-Pi Chang, Wei-Lun Fu
Keywords:   Light emitting-diodes, LEDs, Hydroponic, Red lettuce, Rooftop polytunnel, Urban agriculture.

Abstract. Urban farming could provide both vegetable growers and urban dwellers with more direct access to various fresh vegetables. Nevertheless, certain challenging problems associated with urban farming, including a lack of cultivation space and the effects of urban heat islands, must still be solved. Relatedly, a grower must, in some cases, also know how to utilize various forms of technology, such as lighting systems, as well as factors such as water availability. In this study, an original rooftop polytunnel design for lettuce ( cv. Lollo Rosso) cultivation equipped with a hydroponic system and light emitting diodes (LEDs) is proposed. Various monochromatic lights were also tested for their effects on different quality parameters of lettuce. Specifically, supplemental red (655 nm), blue (445 nm), green (520 nm), and ultraviolet (380 nm) LED lights were used at night to apply photon fluxes of 150, 150, 150, and 20 μmol.m-2.s-1, respectively. The resulting effects of these different colored LEDs on the pigment concentration and growth response of the lettuce grown inside the roof polytunnel were then investigated. The experiment was then repeated several times with different environmental parameters in order to compare the effects of the different light wavelengths under higher temperatures and higher natural irradiation conditions.The results indicated that supplemental red or blue light at night could be strategically employed to maintain low nitrate levels and enhance the nutritional value and growth of lettuce grown in roof polytunnels.

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