Effects of LED Red and Blue Light Component on Growth and Photosynthetic Characteristics of Coriander in Plant Factory

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 (Pn) 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.