Microgreens are immature and tender edible vegetables that have become relevant in the market due to their contribution to human health as “functional food”. They can be produced in controlled environments, allowing more efficient use of space and resources and facilitating the management of environmental conditions, such as light, temperature, and relative humidity. The study’s objective was to evaluate the impact of photoperiod and light intensity on red beet microgreens’ yield and the antioxidant compound content. LED growth lamps (spectrum of 75% red, 23% blue, and 2% far-red) under two photoperiods were evaluated: 12 and 16 h, and three intensity levels: 120 (low), 160 (medium), and 220 (high) µmol m−2 s−1. The largest photoperiod raised 32, 49, and 25% on phenolic compounds, total betalains, and antioxidant capacity, respectively, but a 23% reduction in microgreens yield was obtained compared with the shortest photoperiod. The low and medium intensities promoted the highest yield, reaching 460 g m−2; yield decreased significantly by 22.1% at high intensity compared to low and medium intensity. Contrastingly, no effect on antioxidant activity was observed with the evaluated range intensities, except for the betalains concentration, which was reduced by 35% under the highest intensity compared to low intensity. On the other hand, resource use efficiency (energy and water) improved under the shortest photoperiod. Thus, an intensity between 120 and 160 µmol m−2 s−1 and a photoperiod of 12 h favored the microgreen’s beet growth and saved electricity; meanwhile, a 16 h photoperiod ameliorated the beet microgreens antioxidant activity under a light spectrum composed of blue:red:far-red = 23:75:2.

The spectrum and intensity of light play a significant role in the primary and secondary metabolism of plants. Low intensity can make the photosynthetic process less efficient, while inadequate spectrum can impair plant growth and quality. This study investigates the effect of different LED light spectra at low intensity on germination and growth of lettuce (Lactuca sativa L.) seedlings under a temperature-controlled chamber and the subsequent impact on mature plants grown in a greenhouse under natural light. The purpose was to reach a commercial plant seedling using a low amount of energy to achieve the yield potential in a shorter period. The experiment was carried out in three trials. In trial 1, the effect of different LED light wavelengths [100% blue (B); 100% red (R); mixed light 1 (52% blue, 27% green and 21% red) (BGR1), and mixed light 2 (29% blue, 53% green and 17% red and 1% far red) (BGR2)] at low intensity (55 μmol m–2 s–1 and 12 h light photoperiod) and darkness (control) on germination of two lettuce cultivars [‘Levistro’ (green) and ‘Carmolí’ (red)] was evaluated in a controlled temperature chamber (20±1.2°C). In trial 2, the effect of the same light conditions of the first experiment on agronomic characteristics and pigment contents of lettuce seedlings compared to the natural light (control: 451±66 μmol m–2 s–1) were evaluated. In trial 3, the seedlings developed under different LED light wavelengths were transplanted to evaluate the subsequent effect on the growth of baby lettuce cultivated hydroponically in the greenhouse under natural light. The results of this study show that red wavelength reduced germination percentage, while lights with a higher blue component (B and BGR1) accelerated germination and increased the number of germinated seeds in ‘Levistro’. Red also delayed germination and decreased the number of germinated seeds in ‘Carmolí’ compared to darkness. Seedlings of ‘Levistro’ had a higher fresh weight (FW) than ‘Carmolí’. In addition, FW increased under BGR2 and R, which coincided with the highest number of leaves and leaf length. Nevertheless, fresh weight was higher under BGR2 and B after transplanting, coinciding with the highest number of leaves. A higher blue component of the light (B and BGR1) increased the dry matter percentage (DMP) of seedlings, but there was no significant difference after transplanting. Chlorophyll (CHL) a and b content increased under BGR2; however, the highest CHL a/b ratio was observed under BGR1 in ‘Levistro’ and B in ‘Carmolí’, but it was higher after transplanting when seedlings were grown under B. The anthocyanin (ANT) content of ‘Carmolí’ seedlings was promoted by a higher blue component of the light (B and BGR1) but significantly increased under natural light (control) at the highest intensity. This work shows that varying the spectrum at low intensity can positively modify the growth and biochemical characteristics of lettuce seedlings, although the effect depends on the cultivar. This modification improves the performance of plants during greenhouse growth after transplanting, especially seedlings grown under B and BGR2. Highlights - Blue light enhanced germination and increased the number of germinated seeds of green lettuce. - High blue component lights improved the morphology, dry matter percentage, and chlorophyll a/b ratio of lettuce seedlings. - Blue and full-spectrum lights applied to lettuce seedlings affect fresh weight after transplanting. - The anthocyanin content of seedlings was stimulated by blue light at 55 μmol m–2 s–1, but even more so by PAR of natural light at 451 μmol m–2 s–1.