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Yuyao Kong, Ajay Nemali, Cary Mitchell, and Krishna Nemali

can be quite high in indoor farming ( Barbosa et al., 2015 ; Shimizu et al., 2011 ). Due to their relatively low thermal emissions ( Nelson and Bugbee, 2014 ; Poulet et al., 2014 ), LEDs can be placed close to a canopy to reduce photon losses

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Alexander G. Litvin, Christopher J. Currey, and Lester A. Wilson

inefficiencies increase thermal radiation and operating costs ( Trouwborst et al., 2010 ) and prevent the close proximity of lamps to plants ( Gomez et al., 2013 ). Modern high-intensity LED lighting provides narrow-spectra light including blue (B), red (R), and

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Tessa Pocock

function to maintain photostasis in naturally fluctuating environments, including light. Used frequently now in human applications, LEDs are a disruptive innovation in horticulture and the ability to rapidly control the spectrum, duration, and intensity is

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Theoharis Ouzounis, Eva Rosenqvist, and Carl-Otto Ottosen

light sources in terms of light quality ( Marcelis et al., 2006 ). A recent review by Nelson and Bugbee (2014) claims lack of economic benefits of LED units comparing mainly U.S. produced lamps, where all tested HPS and LED units had a photon

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Arend-Jan Both, Bruce Bugbee, Chieri Kubota, Roberto G. Lopez, Cary Mitchell, Erik S. Runkle, and Claude Wallace

) because it is intended to increase photosynthesis and thus plant growth, whereas photoperiodic lighting only requires a low intensity (1–3 µmol·m −2 ·s −1 ) to regulate flowering of photoperiodic crops. As LED technology developed and became less expensive

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Mark G. Lefsrud, Dean A. Kopsell, and Carl E. Sams

varying wavelengths ( Gauthier et al., 1997 ; Heraut-Bron et al., 2001 ; Quaderi and Reid, 2005 ; Walters and Horton, 1995 ). With the development of light-emitting diodes (LEDs), specific wavelengths of light can now be applied at higher irradiance

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Michael P. Dzakovich, Celina Gómez, and Cary A. Mitchell

producing large amounts of radiant waste heat. Some of the most efficient HPS lamps have an energy conversion efficiency of 1.70 µmol·J −1 , which is commensurate with some of the most efficient LED arrays (1.66 µmol·J −1 ) presently available ( Nelson and

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Allison Hurt, Roberto G. Lopez, and Joshua K. Craver

Lopez, 2014 ). To remedy this issue, greenhouse operations use high-intensity electric lamps to provide SL, with a standard target PPFD of 70 to 90 µmol·m –2 ·s –1 ( Lopez et al., 2017 ). Although HPS lamps are the current industry standard, LEDs have

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Gioia Massa, Thomas Graham, Tim Haire, Cedric Flemming II, Gerard Newsham, and Raymond Wheeler

degradation over time, and the spectral quality cannot, in any practical sense, be altered through the cropping cycle ( Cathey and Campbell, 1980 ). LEDs are currently one of the most promising technologies for CE plant lighting systems ( Massa et al., 2008

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Qinglu Ying, Yun Kong, and Youbin Zheng

(FLs), especially cool white FLs with enhanced blue and red spectra, were traditionally used for indoor production ( Darko et al., 2014 ; Massa et al., 2006 ). Recently, LED lights have been developed as a new electrical light source in crop production