Recently, LEDs with various light qualities have been used in closed plant factories, and they are known to have different effects on the growth and quality of crops. Therefore, this study was conducted to investigate the change in growth and quality in mini red romaine lettuce using LEDs with various light qualities. Wide red spectrum (WRS)-LEDs, blue (B)-LEDs, blue + red (BR)-LEDs, red (R)-LEDs, and white (W)-LEDs were used as the artificial light sources. Regarding growth, the R-LED treatment showed the most positive effect, but the leaf shape was not normal and the Hunter b* value was not suitable because it was higher than that of the other treatments. The Hunter a*, SPAD, and NDVI values of the B- and BR-LED treatments were effective, but this was not the case for those of the R- and W-LED treatments. The anthocyanin reflectance index 1 (ARI1) was 20 times higher in the B-LED treatment than in the R-LED treatment, and the ascorbic acid content was the highest in the WRS-LED treatment. In the sensory evaluation, bitterness and sweetness showed opposite tendencies. Regarding the overall preference, the BR-LED treatment received the highest score. Correlation analysis showed that the bitterness was closely correlated with the anthocyanin content and leaf color. Taken together, BR-LEDs provided a good top fresh weight, dark red leaves, and high anthocyanin and ascorbic acid contents, with the highest overall preference; therefore, BR-LEDs were the most suitable for the cultivation of mini red romaine lettuce.

This study investigated the effects of supplemental inter-lighting on paprika (cv. Nagano RZ) in South Korea in summer using various LED light sources. The following LED inter-lighting treatments were used: QD-IL (blue + wide-red + far-red inter-lighting), CW-IL (cool-white inter-lighting), and B+R-IL (blue + red (1:2) inter-lighting). To investigate the effect of supplemental lighting on each canopy, top-lighting (CW-TL) was also used. Additionally, a control without supplemental lighting was included for comparison. Significant variations were observed in the plant growth indexes 42 days after treatment. The SPAD values and total chlorophyll content in the last period of cultivation were significantly higher than those of the control. In November, the marketable fruit yield was significantly higher than that of the control. QD-IL, CW-IL, and CW-TL resulted in significantly higher values of total soluble solids than the control, and CW-IL resulted in higher values of ascorbic acid content than the control. Regarding the economic analysis, CW-IL resulted in the highest net income rate (12.70%) compared with the control. Therefore, the light sources of CW-IL were assessed as suitable for supplemental lighting due to the highest total soluble solids, ascorbic acid content, and net income rate obtained.

Light quality can be stated to be the identity of an artificial light source, and although the response of light quality may vary depending on the crop, the effect is clearly visible and can produce various results depending on the combination of an artificial light source. This study investigated the spectral reflectance, photosynthetic performance, and chlorophyll fluorescence of mini green romaine lettuce based on light quality. Most parameters related to spectral reflectance showed the best results under blue light, and photosynthetic performance was more effective with mixed light than with single-colored light, among which blue + red (BR)-LED was the most suitable. Red light was ineffective, showing mostly low results in parameters of spectral reflectance and photosynthetic performance. In the case of chlorophyll fluorescence, the light quality influenced photomorphogenesis, resulting in increased leaf length and width with R- and quantum dot (QD)-LED, which expanded the leaf area and allowed for more external light to be captured (ABS/RC and TRo/RC). However, the ratio of electronized energy (ETo/RC) was low, and the amount of energy dissipated as heat (DIo/RC) was high. Consequently, the degree of electron acceptor reduction and overall photosynthetic performance (PI_ABS and PI_total) were lower compared to other light qualities. Additionally, the contrasting results of QD-LED and BR-LED were attributed to the form of red light and the presence or absence of far-red light when comparing spectra. Principal component analysis also clearly distinguished light qualities for photosynthesis and growth. Growth was increased by red (R)- and QD-LED, while photosynthetic performance was increased by BR- and blue (B)-LED.

This study was conducted to investigate effects of LED light quality on the growth and photomorphogenesis of basil (cv. ‘Amethyst Improved’) in a closed-type plant factory. Basil was sown on a urethane sponge and grown for two weeks under a White-LED. When the first main leaf appeared, the plants were transplanted into a nutrient solution hydroponic system (24 ± 2 °C, RH 55±10%) and using a standard nutrient solution for leafy vegetables (N 17.3, P 4.0, K 8.0, Ca 8.0, Mg 4.0, S 4.0 me·L^-1). To compare growth and internal traits of basil under various light qualities, QD-LED (combining blue, red, and far-red light), Blue+Red-LED (blue and red wavelengths at a ratio of 1:3), White-LED, 100% Blue-LED, and 100% Red-LED were used to cultivate basil for 35 days. Photosynthetic photon flux density (PPFD) was 200 ± 10 μmol·m-2·s^-1 and the light was provided for 16/8 hours (Light/Dark). The plant height was significantly the longest at 26.1 cm in QD-LED, and the number of leaves was the highest at 16.00 ea in QD-LED, but not significant. The leaf length was the longest at 10.9 cm in QD-LED and the shortest at 8.10 cm in White-LED. The leaf width was up to 26% wider in Blue+Red-LED, but there was no statistical significance. The leaf thickness was the thickest at 0.33 mm for Blue+Red-LED and Red-LED, which have a high proportion of red light, and the thinnest at 0.26 mm for Blue-LED. In the case of the curvature index (CI), which indicates the morphological characteristics of basil leaves, the values were highest for Blue+Red-LED and Red-LED. The internode length and leaf stalk length were significantly the longest at 5.73 cm and 3.04 cm, respectively, for QD-LED, and the stem diameter at 5.26 mm for QD-LED. The shoot fresh weight was 26.0 g in QD-LED, which was significantly higher than the other treatment groups by up to four times, but the root fresh weight was the highest at 5.99 g in Blue+Red-LED. On the other hand, the shoot and root dry matter ratio were the highest at about 9% and 5%, respectively, in White-LED. The maximum quantum yield (FvFm) did not differ significantly between the treatment groups, but the value was significantly lowest at 0.79 for Red-LED. The chlorophyll content (SPAD), normalized difference vegetation index (NDVI), and anthocyanin reflectance index (ARI1) values were up to 27% higher in Blue+Red-LED than in other treatment. Also, the DPPH radical scavenging activity and total phenol content were the highest in Red-LED at 74% and 9.47 mgGAE·g^-1FW, respectively. As a result, basil (cv. ‘Amethyst Improved’) grew best in QD-LED, and its antioxidant effect was the best in Red-LED. In addition, it was confirmed that the curvature and morphological characteristics of basil leaves changed depending on the ratio of red light at 600-700 nm.

This study investigated the effects of four LED light qualities, red+blue+far-red (WRS-LED), blue+red (BR-LED), blue (B-LED), and red (R-LED), and exogenous L-glutamic acid at 10 ppm on the growth and quality of red mustard spinach (Brassica rapa var. perviridis) cultivated in a plant factory using a recirculating deep-flow hydroponic system. Plants were exposed to four LED light quality treatments at 180 ± 10 μmol·m⁻²·s⁻¹ PPFD for 28 days after transplanting. L-glutamic acid at 10 ppm was applied once to the recirculating nutrient solution 15 days after transplanting, resulting in 13 days of exposure prior to final harvest on day 28. All growth and quality parameters were measured at the final harvest after 28 days of cultivation. WRS-LED promoted the greatest biomass production. Additionally, vitamin C content, DPPH radical scavenging activity, and total phenolic content were highest under BR-LED and B-LED conditions. Notably, under B-LED, L-glutamic acid treatment increased total phenolic content to approximately twice that of the control. Leaf redness, expressed as Hunter a* values, was observed exclusively under BR-LED. Principal component analysis revealed that LED light quality was the primary determinant of treatment responses, with growth-related traits associated with WRS-LED and R-LED, and quality-related traits with B-LED and BR-LED. Overall, BR-LED combined with L-glutamic acid represents the most suitable treatment for red mustard spinach cultivation in plant factories, achieving a favorable balance between growth and nutritional quality.