The aim of this study was to investigate the effects of green light, added with red and blue LEDs, on the growth, leaf microstructure and quality of spinach plants. Plants were transplanted and grown hydroponically for 30 days under different combinations of red:blue with a 4:1 ratio (R4B1), red:blue:green with a 5:2:3 ratio (R5B2G3) and red:blue:green with a 1:1:1 ratio (R1B1G1), at a 190 µmoL m−2·s−1 photosynthetic photon flux density (PPFD). The results showed that green light, added to red and blue LEDs at a reasonable ratio, could reduce the growth, leaf microstructure and quality of spinach plants, but not the organic acid content. The highest values for the growth parameters, photosynthetic pigments, leaf structure characteristics and quality of the spinach plant were observed for the R4B1 treatment, but not for the organic acid content. Therefore, our results suggest that green light added to red and blue LEDs at a reasonable ratio is not suitable for the growth of spinach.

This study aimed to evaluate the effect of four light intensities (90, 140, 190 and 240 µmol m-2 s-1) provided by red-blue LED light (spectrum ratio: R660/B450 = 4/1) on the growth and quality of hydroponic cultivated spinach. The results showed that when the light intensity increased, plant height, leaf number, root length, leaf width, shoot fresh weight, shoot dry weight, root fresh weight and root dry weight were increased but specific leaf weight and shoot-to-root ratio did not increase. The highest values of growth parameters were observed under 190 µmol m-2 s-1 treatment, while the lowest values were observed under 90 µmol m-2 s-1 treatment. At higher light intensities, K+, oxalic acid and nitrate contents tended to decrease but not Ca2+ content. Meanwhile, the highest values of Fe2+, crude fiber, soluble-solids, total polyphenol and vitamin C contents were observed under 190 µmol m-2 s-1 treatment, but 190 µmol m-2 s-1 treatment showed the lowest organic acid content. Our results indicated that among all experimental lighting treatments, 190 µmol m-2 s-1 light intensity showed the best effect on the growth and quality of hydroponic cultivated spinach.