Utilization Efficiencies of Electric Energy and Photosynthetically Active Radiation of Lettuce Grown under Red LED, Blue LED and Fluorescent Lamps with Different Photoperiods

Abstract

This study was conducted to analyze the utilization efficiencies of electric energy and photosynthetically active radiation of lettuce grown under red LED, blue LED and fluorescent lamps with different photoperiods. Methods: Red LED with peak wavelength of 660 nm and blue LED with peak wavelength of 450 nm were used to analyze the effect of three levels of photoperiod (12/12 h, 16/8 h, 20/4 h) of LED illumination on light utilization efficiency of lettuce grown hydroponically in a closed plant production system (CPPS). Cool-white fluorescent lamps (FL) were used as the control. Photosynthetic photon flux, air temperature and relative humidity in CPPS were maintained at 230 μmol‧m −2 ‧s −1 , 22/18°C (light/darkness), and 70%, respectively. Electric conductivity and pH were controlled at 1.5-1.8 dS‧m −1 and 5.5-6.0, respectively. The light utilization efficiency based on the chemical energy converted by photosynthesis, the accumulated electric energy consumed by artificial lighting sources, and the accumulated photosynthetically active radiation illuminated from artificial lighting sources were calculated. Results: As compared to the control, we found that the accumulated electric energy consumption decreased by 75.6% for red LED and by 70.7% for blue LED. The accumulated photosynthetically active radiation illuminated from red LED and blue LED decreased by 43.8% and 33.5%, respectively, compared with the control. The electric energy utilization efficiency (EEUE) of lettuce at growth stage 2 was 1.29-2.06% for red LED, 0.76-1.53% for blue LED, and 0.25-0.41% for FL. The photosynthetically active radiation utilization efficiency (PARUE) of lettuce was 6.25-9.95% for red LED, 3.75-7.49% for blue LED, and 2.77-4.62% for FL. EEUE and PARUE significantly increased with the increasing light period. Conclusions: From these results, illumination time of 16-20 h in a day was proposed to improve the light utilization efficiency of lettuce grown in a plant factory.

Spectral Quality of Light Can Affect Energy Consumption and Energy-use Efficiency of Electrical Lighting in Indoor Lettuce Farming

“…Initial increase in SDW, and thereby EUE, with increasing R:B was likely due to a positive effect of greater percentage of red on lettuce growth. Leaf expansion and shoot growth of lettuce were shown to be greater under red light in other studies (Kang et al, 2016;Lee and Kim, 2013;Poulet et al, 2014;Wang et al, 2016;Wojciechowska et al, 2015;Zhang T. et al, 2018). In addition, a negative effect of a greater fraction of blue light on leaf and shoot growth in lettuce was also previously reported (Hoenecke et al, 1992;Tosti et al, 2018).…”

“…This suggests that EUE can be lower when a greater proportion of red light is emitted by phosphor due to a larger ''down conversion'' involved (blue vs. red) and increased wastage of electrical energy in the form of heat as a result. In contrast, a greater proportion of red light in the incident light may be preferred for lettuce production as it increases leaf expansion and shoot growth (Kang et al, 2016;Lee and Kim, 2013;Wang et al, 2016;Zhang X. et al, 2018). Thus, the spectral quality of LEDs can potentially influence EUE by affecting both SDW and EEC in opposite ways.…”

Analysis of Growth Parameters for Crop Vegetables under Broad and Narrow LED Spectra and Fluorescent Light Tubes at Different PPFs

“…Son and Oh (2013) also reported the highest fresh weight with the monochromatic R LED treatment, when compared lettuce growing under 100% R and different combinations of R and B light. Lee and Kim (2013) also working with lettuce and comparing fluorescent lamps with red and blue monochromatic LEDs, verified the same trend, fresh and dry weight increased in R and decreased in B, when compared to the fluorescent control.…”

A framework of artificial light management for optimal plant development for smart greenhouse application

“…In a similar study, Hiroki et al [ 14 ] used the same 16-hour light photoperiod but varied the light period from 18 to 24 hours and showed that a shorter period has the best growth in lettuce albeit at the expense of high energy consumption. On the specific effect of photoperiod on lettuce growth, [ 15 ] and [ 16 ] both reported that the preferred photoperiod range is between 16- to 20-hour light. The speed breeding method [ 17 ] introduced by Watson et al, marks the culmination of the importance of photoperiod in improving crop productivity, where the productivity of crops such as wheat and barleys that are subjected to extended light exposure (up to 22-hour light) have been experimentally shown to accelerate by at least twofold [ 17 ].…”