APPLICATIONS OF FAR-RED LIGHT EMITTING DIODES IN PLANT PRODUCTION UNDER CONTROLLED ENVIRONMENTS
Light emitting diodes (LEDs) are a potential supplemental light source to provide select light quality in plant production. Far-red (FR, 700-800 nm) LEDs, despite the plant biological significance, have limited availability in the market, compared with that of red (600-700 nm) or near infrared (~800 nm or longer) LEDs. This is because FR light has no value in human or industrial applications (such as machine vision). However, with possible phase-out of the use of incandescent lamps (the conventional source of FR) worldwide, greater demand is expected for FR LEDs in horticultural applications. Moreover, the LED technology that allows pure FR light permits applications beyond traditional applications of FR rich lighting to control flowering. Our research group has worked on applications of FR lighting in food crop and transplant production, including morphology control of grafting rootstock seedlings or promoting growth of baby leaf lettuce plants. Using FR lighting at end of day (EOD), tomato and squash rootstock hypocotyls were elongated to a desirable length (22-43% greater than non-treated control) and the response was saturated at a small dose of pure FR (2-4 mmol m-2 d-1). This FR dose requirement was translated to various combinations of FR light intensity, duration, and light-delivery methods, suitable for a greenhouse plant production system. We also demonstrated that supplemental FR lighting in baby leaf production enhanced the fresh and dry mass of lettuce plants (115-128% of the control), caused by the increased light interception as a result of extending leaf area. However, EOD-FR did not cause significant growth promotion for lettuce in greenhouse. More research is necessary to develop feasible FR lighting system to make the technology readily available in specialty crop industry.
Kubota, C., Chia, P., Yang, Z. and Li, Q. (2012). APPLICATIONS OF FAR-RED LIGHT EMITTING DIODES IN PLANT PRODUCTION UNDER CONTROLLED ENVIRONMENTS. Acta Hortic. 952, 59-66
end-of-day, baby leaf, grafting, hypocotyle, interspecific squash, light quality, phytochrome, rootstock