An overview of the recent developments and current status on the preharvest application of LED technology in controlled environment agriculture

Figures & data

Figure 1. Conventional light sources previously used in agriculture (a- Fluorescent light; b-HPS (High pressure sodium) light and c-incandescent light) and full spectrum light emitting diode (d).

Figure 2. Absorption spectrum of photosynthetic organs (adopted from https://www.ledgrowlightshq.co.uk/chlorophyll-plant-pigments/).

Table 1. Effects of various LED light spectra on horticultural species.

Light supplemented	Commodity	Effects on plants	Reference
White, red and blue LED lights	Butterhead and romaine lettuce (L. sativa var. capitata)	White LEDs with shorter blue peak wavelength (437 nm) enhanced the growth and development of lettuce.	T. K. L. Nguyen et al. (2021)
Red (R), blue (B) and far-red (FR) LED lights and their combination (R + B, R + FR, B + FR, R + B + FR)	Brassica microgreens	The influence of LED light wavelengths on the major growth and nutritional quality as well as the glucosinolates were dependent on the species.	Demir et al. (2023)
Red and Blue (RB), Red and Blue + Far-Red (FR) with an intensity of 180 µmol m^−2 s^−1 for Red and Blue, plus 44 µmol m^−2 s^−1 for Far-Red	Tomatoes (Solanum lycopersicum ‘Siranzo’)	In this study, red plus blue LED light and the far-red light increased fruit firmness and maintained the concentration of lycopene and β-carotene which are the most important carotenoids in tomatoes.	Appolloni et al. (2023)
White, purple, blue, red light, green light, yellow, red – blue light in a 9:1 ratio, and red – blue light in a 4:1 ratio (4 R/1B).	Lettuce(Lactuca sativa)	Purple, blue, red, and the red-blue light combination increased the biomass of the aboveground part of lettuce, while the treatments with red or blue enhanced soluble protein, free amino acids, and vitamin C.	T. Zhang et al. (2018)
Red, blue, and red + blue LEDs (1:1)	Super-Hot chilli (Capsicum annuum)	Supplemental blue LED light at 100–200 μmol m^−2s^−1 showed higher growth and yield of chilli plants than control but did not differ with red or mix LED (red + blue).	Yap et al. (2021)
Three blue peak emission wavelengths with photosynthetic photon flux density (PPFD) maintained at 200 ± 10% μmol m^−2 s^−1	Kale (Brassica oleracea L. var. acephala)	Different wavelengths did not affect plant biomass nor leaf physical characteristics but enhanced the concentration of carotenoids and chlorophylls in kale leaves.	Ashenafi et al. (2023)
Red and blue (R:B) (30:70, 50:50, and 70:30) emitting 80, 100, and 150 µmol m^−2 s^−1 respectively	Cucumber (Cucumis sativus L)	Cucumber seedlings grown under the 70 R:30B showed a significant increase in growth as well as photosynthetic capacity.	Hamedalla et al. (2022)
Red LED was combined with a blue LED light at a ratio of (1:1) with a combined photosynthetic photon flux density (PPFD) of 138 ± 5 µmol m^−2 s^−1	Tomato (Solanum lycopersicum)	The treatment enhanced growth, yield, and antioxidant phytonutrients in tomato plant and fruit.	Ngcobo et al. (2022)
Green, yellow and purple LED lights	Lettuce (Lactuca sativa L. var. youmaicai)	Green, yellow and purple light significantly regulated the biomass, photosynthesis and soluble sugar content in lettuce	H. Liu et al. (2018)
Yellow light, green light, and blue LED lights	Potato plantlets (Solanum tuberosum L.)	The addition of yellow to the combined spectra of red and blue contributed positively to the growth, development, and morphogenesis	H. Liu et al. (2018)

Table 2. Effects of various LED wavelengths on horticultural crops grown hydroponically.

Lighting supplemented	Commodity	Effects on plants	Reference
The hydroponic spinach plants were grown under four light spectra: LED lamps with ratio of red to blue light (R:B ratio) of 0.9, 1.2, and 2.2 and fluorescent lamps with R:B ratio of 1.8 as control	Spinach (Spinacia oleracea L.)	Th LED lights with different R:B ratios significantly enhanced growth, and nutritional quality and spinach yield.	Gao et al. (2020)
Continuous light (CL) for 48 h was combined with red and blue LEDs supplemented with or without green LED	Lettuce (Lactuca sativa L. cv. capitata (Butterhead)	In this study, green light supplementation significantly increased nitrate reductase (NR) and nitrite reductase (NiR), glutamate synthase (GOGAT) and glutamine synthetase (GS) activity. The same treatment improved the nutritional quality and photosynthetic rates.	Bian et al. (2018)
The following experimental LED treatments were exposed to Kale plants: 1) white LED for 37 d; 2) 5% Blue/95% Red for 37 d; 3) 20% Blue/80% Red for 30 d; 4) 20% Blue/80% Red for 25 d; 5) 20% Blue/80% Red for 20 d; and 6) 20% Blue/80% Red for 15 d prior to harvest	Kale (Brassica oleracea var. acephala)	The study found that shifting to higher blue light LED treatments closer to harvest result in decreased plant height and increased leaf width of the kale plants.	Metallo et al. (2018)
The effect of white – green light (W:G = 4:1, W4G1), red – green light (R:G = 4:1, R4G1), red – green – blue light (R:G:B = 4:1:1, R4G1B1), and four types of red – blue lights (R:B = 3:1, R3B1; R:B = 2:1, R2B1; R:B = 1:1, R1B1; R:B = 1:6, R1B6) was investigated in hydroponically grown wheat	Winter wheat (Triticum aestivum L., cv. zhongmai 1062)	Regardless of growth rate and production, winter wheat grown under various LED light treatments produced grains; more notably, R4G1 treatment enhanced growth, yield and starch content significantly	Guo et al. (2023)
A combination of red and blue LEDs (R660/B450 = 80/20) at different light intensities (90, 140, 190 and 240 µmol/m^2/s^−1) on the growth, photosynthesis, and leaf microstructure of hydroponic cultivated spinach	Spinach (Spinacia oleracea L.)	The authors found that 190 µmol/m^2/s^−1 light intensity as the appropriate intensity for growth of spinach	T. Nguyen et al. (2019)
The effects of high light irradiation (HLI, 500 μmol m^−2·s^−1) provided by red and blue LEDs (4 R:1B) on lettuce grown was evaluated	Purple lettuce (Lactuca sativa var. ‘Zishan’)	The study revealed that short-term HLI promotes biomass production and enhances secondary metabolite production in lettuce	Shao et al. (2020)

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Data availability statement

Data sharing is not applicable to this article as no new data were created or analysed in this study.