Supplemental upward LED lighting for growing romaine lettuce {Lactucasativa) in a plant factory: cost performance by light intensity and different light spectra

摘要

Numerous studies have established that the closed plant-production system is a powerful and effective means to supply safe and high-quality vegetables in urban areas. However, few studies have focused on reducing plant organic residues in the closed plant-production system, i.e., senescent leaves and roots that are nonsalable parts of the produced plants. Supplying upward lighting is considered as a method to improve the light environment beneath the plant canopy, enhance plant production, and reduceresidues. This study compares the electricity usage and energy-use efficiency in growing romaine lettuce with and without supplemental upward LED lighting. Four light spectra (white, blue, green, and red) and two light intensities [30 and 60 umol nr2 s1photosynthetic photon flux density (PPFD)] of upward lighting were tested. The red LEDs showed the largest increment in saleable yield both nr2 and kWh1 under supplemental upward lighting, followed by blue, white, and green, in that order. Under the market conditions prevailing in Tokyo, Japan, supplemental upward lighting is highly economically viable, particularly for higher levels of light intensity and for red and blue LEDs. With a light intensity of 60 pmol nr2 s1 PPFD, the breakeven price of electricity kWh1 is estimated to be US$ 1.00, 0.70, 0.55, and 0.35, respectively, for red, blue, white, and green LEDs.