Coriander is a whole-plant edible micro vegetable frequently used in the food industry. Its fresh eating features give it a flavor that is both tasty and refreshing, as well as potentially dangerous due to the bacteria (e.g., Shigella sonnei) it may contain. Artificial light-based plant factories are becoming increasingly popular due to the development of light-emitting diodes (i.e., LEDs). These plant factories employ artificial light to recreate the ideal lighting conditions for photosynthesis, ensuring plant yield and safety. Red (R) light and blue (B) light are essential for crop development and photosynthesis because R light and B light correspond to the wavelength absorption peaks of chlorophyll. However, the sensitivity of various crops to the light of varying wavelengths varies. Here, we determined the ideal R to B light ratio for cultivating coriander in plant factories by evaluating the photosynthetic characteristics of coriander (‘Sumai’) under different red–blue ratios. Specifically, we used monochrome red (R) and blue (B) light as controls and evaluated a total of seven different ratio treatments of R and B light (R, R:B = 5:1 (R5B1), R:B = 3:1 (R3B1), R:B = 1:1 (R1B1), R:B = 1:3 (R1B3), R:B = 1:5 (R1B5), B) under the background of uniform light intensity (200 ± 10 μmol m⁻² s⁻¹) and photoperiod (16-h/8-h light/dark). The results showed that the total yield of R:B = 3:1 (R3B1) was 16.11% and 30.61% higher than monochrome R and B treatments, respectively, the photosynthetic rate (P_n) and stomatal density were increased, and the nitrate content was decreased. Monochromatic light has adverse effects on crops. Monochromatic R light reduces the CO₂ assimilation amount. Monochromatic blue light treatment lowers chlorophyll concentration and net photosynthetic rate.

The effects of red and blue light on growth and steady-state photosynthesis have been widely studied, but there are few studies focusing on dynamic photosynthesis and the effects of LED pre-treatment on cucumber seedlings’ growth, so in this study, cucumber (Cucumis sativus L. cv. Jinyou 365) was chosen as the test material. White light (W), monochromatic red light (R), monochromatic blue light (B), and mixed red and blue lights with different red-to-blue ratios (9:1, 7:3, 5:5, 3:7, and 1:9) were set to explore the effects of red and blue light on cucumber seedlings’ growth, steady-state photosynthesis, dynamic photosynthesis, and subsequent growth under fluctuating light. The results showed that compared with R and B, mixed red and blue light was more suitable for cucumber seedlings’ growth, and the increased blue light ratios would decrease the biomass of cucumber seedlings under mixed red and blue light; cucumber seedlings under 90% red and 10% blue mixed light (9R1B) grew better than other treatments. For steady-state photosynthesis, blue light decreased the actual net photosynthetic rate but increased the maximum photosynthetic capacity by promoting stomatal development and opening; 9R1B exhibited higher actual net photosynthetic rate, but the maximum photosynthetic capacity was low. For dynamic photosynthesis, the induction rate of photosynthetic rate and stomatal conductance were also accelerated by blue light. For subsequent growth under fluctuating light, higher maximum photosynthetic capacity and photoinduction rate could not promote the growth of cucumber seedlings under subsequent fluctuating light, while seedlings pre-treated with 9R1B and B grew better under subsequent fluctuating light due to the high plant height and leaf area. Overall, cucumber seedlings treated with 9R1B exhibited the highest biomass and it grew better under subsequent fluctuating light due to the higher actual net photosynthetic rate, plant height, and leaf area.