This study aimed to investigate the influence of red, blue, green, and yellow light–emitting diode (LED) lights with varying intensities and ratios on the photosynthetic efficiency of Boston lettuce and Ziyan lettuce; treatments were conducted using four LED lights, namely red (R), blue (B), green (G), and yellow (Y) LED lights; a light intensity of 120 μmole.m^−2.s^−1 and CO_2 concentration of 1000 ppm were applied. With respect to triple light combinations, the highest photosynthetic efficiency was observed in Boston lettuce under RBG treatment (R, 32%; B, 48%; G, 20%) and in Ziyan lettuce under RBY treatment (R, 36%; B, 54%; Y, 10%), indicating that different light combinations are required for the two types of lettuce. The plant growth, leaf pattern, nitrate level, and electric power consumption of Boston lettuce (under G, RB, and RBG treatments), Ziyan lettuce (under R, RB, and RBY treatments), and a control group (under white LED light [W]) were compared. The results indicated that Boston lettuce under RBG treatment produced a denser leaf pattern and deeper colors; its growth was inferior, but its nitrate level and electric power consumption were lower relative to those under G and W treatments. Ziyan lettuce under RBY treatment produced deeper leaf colors, but its growth did not differ significantly from that of Ziyan lettuce under R treatment; its nitrate level and electric power consumption were lower. The two aforementioned types of lettuce were suitable for consumption. The findings indicated that optimal photosynthetic efficiency improved the nitrate metabolism in plants and reduced power consumption. The growth pattern achieved with a lighting mode that promotes optimal photosynthetic efficiency has greater commercial value and can be applied in plant factories for mass–producing lettuce that meets consumption standards, thereby providing better food safety for consumers.
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