Supplemental upward LED lighting for growing romaine lettuce (Lactuca sativa) in a plant factory: cost performance by light intensity and different light spectra
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 reduce residues. 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 µmol m-2 s-1 photosynthetic photon flux density (PPFD)] of upward lighting were tested. The red LEDs showed the largest increment in saleable yield both m-2 and kWh-1 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 µmol m-2 s-1 PPFD, the break-even price of electricity kWh-1 is estimated to be US$ 1.00, 0.70, 0.55, and 0.35, respectively, for red, blue, white, and green LEDs.
Saengtharatip, S., Lu, N. and Takagaki, M. (2018). Supplemental upward LED lighting for growing romaine lettuce (Lactuca sativa) in a plant factory: cost performance by light intensity and different light spectra. Acta Hortic. 1227, 623-630
bottom LED lighting, energy-use efficiency, electricity usage, saleable leaf, vertical farming, waste reduction