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Ricardo Hernández and Chieri Kubota

, 2014 ; Philips-Electronics, 2012 ). An alternative to HPS is the high-intensity LEDs, which currently have reportedly a PPF efficiency ranging between 0.84 and 2.3 μmol·J −1 ( Nelson and Bugbee, 2013 , 2014 ; Philips, 2014 ) and are projected to

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Yuya Mochizuki, Saori Sekiguchi, Naomi Horiuchi, Thanda Aung, and Isao Ogiwara

to changes in the light environment by controlling their morphology using receptors such as phytochromes, cryptochromes, and phototropin ( Ballare and Casal, 2000 ). Recently, LEDs came to the forefront as a light source in greenhouses because LEDs

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Dean A. Kopsell, Carl E. Sams, and Robert C. Morrow

active pigments based on wavelength ( McCree, 1973 ). Thus, the spectral distribution of light sources in plant production will determine photomorphogenic responses. LEDs now provide the option of selecting specific wavelengths to complement photoreceptor

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Joshua R. Gerovac, Joshua K. Craver, Jennifer K. Boldt, and Roberto G. Lopez

were initially used as the standard light source, growers have begun replacing them with LED arrays. Several operations worldwide have implemented this technology as LEDs have become more economically viable due to increased efficiency and decreased

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Daedre S. Craig and Erik S. Runkle

very energy-inefficient and are being phased out of production in many parts of the world ( Waide, 2010 ). LEDs are an attractive technology for NI lighting of photoperiodic crops. Compared with conventional lamps, LEDs have many desirable

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Heidi Marie Wollaeger and Erik S. Runkle

( Cucumis sativus ) plants under an artificial sunlight spectrum, an artificial shade spectrum [greater far-red (>680 nm) light], and under B LED (peak = 445 nm) light ( PPF = 100 μmol·m −2 ·s –1 ; 16-h photoperiod). The highest QE recorded was R light

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Heidi M. Wollaeger and Erik S. Runkle

Blue (B; 400–500 nm) and red (R; 600–700 nm) light are generally considered the most efficient wavelengths for eliciting photosynthesis in plants ( McCree, 1972 ; Sager et al., 1988 ). Therefore, B and R LEDs with peak light emission that coincides

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Wesley C. Randall and Roberto G. Lopez

seedlings, also known as young plants or plugs, have led to a large increase in finish plant quality and profitability ( Armitage and Kaczperski, 1994 ; Kuehny et al., 2001 ). Young plant production occurs in late winter and early spring when the integrated

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Hunter A. Hammock, Dean A. Kopsell, and Carl E. Sams

( Mitchell et al., 2015 ). Before the advent of LEDs, special filters were used to alter the spectral quality of broad-spectrum growth lamps with varied success. LEDs provide researchers the opportunity to determine how light quality fundamentally impacts

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Christopher J. Currey and Roberto G. Lopez

of HPS bulbs (up to 450 °C) necessitates adequate separation or distance between lamps and plants to avoid leaf scorch. LEDs are solid-state, semiconducting diodes that can emit light from ≈250 nm to 1000 nm or greater ( Bourget, 2008 ). Although low