A plant factory with artificial light (PFAL) is defined as an advanced agricultural production system with a precisely controlled environment, playing an important role in vertical farming and urban food supply. Artificial light is one of the core technologies in PFALs and accounts for a large part of energy consumption; elevating the light utilization efficiency of plants is vital for the sustainable development of PFALs. Meanwhile, the enclosed structure of the plant factory resulted in the independence of its light environment, indicating that the light environment in PFALs can be custom-made. Lighting strategy is an attempt to reprogram the light environmental parameters in unconventional ways, resulting in innovative lighting modes for energy-saving, high-yield, and high-quality production in PFALs. This article reviewed the recent endeavors aiming to increase light conversion efficiency and nutritive properties of crops by different lighting strategies, providing economic irradiation patterns or modes for various PFALs production goals.

Anthocyanins are widely common natural antioxidants and represent an important economic feature in vegetables, but the potential response of UVA–blue co-irradiation on the anthocyanin biosynthesis of pak choi is not clear. Here, we investigated the effects of the supplement of four doses of UVA to blue light on growth, metabolites and the anthocyanin biosynthesis of two cultivars of pak choi. The results revealed that supplementing UVA light to blue light positively affected the growth of the pak choi and elevated the soluble protein content and antioxidant capacity. Especially, when compared with a monochromatic blue light, the anthocyanin synthesis was enhanced with an increase in UVA light strength, which reached a peak value at the strength of 10 μmol·m⁻²·s⁻¹. Further study revealed that the UVA–blue co-irradiation enhanced the transcription of partial light-induced and anthocyanin structural genes. The intraspecific difference in the expression patterns of MYB1 and PAP1 were observed in these two tested cultivars. MYB1 was significantly up-regulated in red-leaf pak choi, but down-regulated in purple-leaf pak choi. On the contrary, PAP1 was significantly up-regulated in purple-leaf pak choi, but down-regulated in red-leaf pak choi. To sum up, this study established an efficient pre-harvest lighting strategy to elevate the economic value of pak choi.

Our previous study revealed a significant effect of red and blue light on steady-state and dynamic photosynthesis in cucumber seedlings. To further investigate the mechanism by which red and blue light affect photosynthesis, cucumber (Cucumis sativus L. cv. Jinyou 365) seedlings were exposed to white light (W), monochromatic red light (R), monochromatic blue light (B), and mixed red–blue light with red:blue photon flux ratios of 9:1 (9R1B), 7:3 (7R3B), 5:5 (5R5B), 3:7 (3R7B), and 1:9 (1R9B). We measured photosynthetic pigment contents, induction curves of photosynthetic gas exchange and chlorophyll fluorescence parameters during low-to-high-light transition, as well as the activities and gene expression of key Calvin cycle enzymes. The results showed that B yielded higher photosynthetic pigment contents than R, although both remained lower than W. Mixed red–blue light with a blue-light ratio above 50% produced significantly higher pigment contents than W. Under low light, blue light exhibited negligible effects on photosynthesis. In contrast, under high light, 7R3B, 5R5B, 3R7B and 1R9B elevated net photosynthetic rate (A) and stomatal conductance (Gs). Among these, 7R3B, 5R5B and 3R7B also accelerated photoinduction, as reflected by a shorter time to reach 90% steady-state net photosynthetic rate (T_90%A). Chlorophyll fluorescence parameters changed rapidly and attained a steady state within 5 min during light induction. During photoinduction, biochemical limitation was severe in the early stage but declined rapidly, while stomatal limitation appeared in mid-induction and persisted into the late stage; photochemical limitation remained minor, and the severity of these limitations was modified by light quality. Red and blue light exerted negligible effects on chlorophyll fluorescence parameters under low light. However, blue light enhanced the relative electron transport rate of PSII under high light by elevating the fraction of open PSII centers. Furthermore, blue light significantly increased the activities and gene expression of key Calvin cycle enzymes. Correlation analysis revealed that higher chlorophyll contents were positively associated with A and Gs under high light but showed no significant correlation with photoinduction. Higher A and Gs under both low- and high-light intensities were associated with faster photoinduction.