Lettuce exposed to red (R) and blue (B) LEDs (4R:1B, 200 μmol·m⁻²·s⁻¹) were cultivated hydroponically in an environmentally controlled plant factory to examine the effects of light–dark cycle (LDC) conversion at pre-harvest stage on the growth, phytochemical, and photosynthetic pigment accumulation of lettuce. Lettuce plants of four groups were firstly cultivated with the same LDC of 16/8 h (light/dark) for fourteen days. Six days before harvest, the LDC of three groups were altered to 8/4 h (T12), 24/12 h (T36), and 32/16 h (T48), respectively. The last group had invariable photoperiod and was concerned as control (CK, 16/8 h). The results showed that T12 and T36 significantly improved while T48 reduced leaf area and shoot fresh and dry weight of lettuce compared with the CK. The plants treated with altered LDC had higher phytochemicals (soluble sugar, soluble protein, and ascorbate) and photosynthetic pigments (chlorophyll and carotenoids) contents than the CK, but the starch and nitrate contents of the CK were higher. These results suggested that the yield and nutritional quality of lettuce can be increased by changing the LDC properly in the later growth stage. But if the light–dark period was too long, it would have negative effects on the growth of lettuce. In addition, shorten the LDC at pre-harvest stage promoted better production yield and nutritional quality based on the same electricity consumption.

生菜暴露于红色（R）和蓝色（B）LED（4R：1B，200μmol·m ^-2 ·s ^-1）在环境受控的植物工厂中进行水培，以研究收获前阶段的光暗循环（LDC）转化对生菜生长，植物化学物质和光合色素积累的影响。首先将四个组的莴苣植物在相同的16/8小时LDC（亮/暗）下培养14天。收获前六天，三组的LDC分别更改为8/4 h（T12），24/12 h（T36）和32/16 h（T48）。最后一组具有不变的光周期，并作为对照（CK，16 / 8h）。结果表明，与CK相比，T12和T36显着改善，而T48减少了叶面积，并发芽了新鲜和干重的生菜。用改变的最不发达国家处理的植物具有更高的植物化学成分（可溶性糖，可溶性蛋白，和抗坏血酸）和光合色素（叶绿素和类胡萝卜素）的含量高于CK，但CK的淀粉和硝酸盐含量更高。这些结果表明，通过在生长期后期适当改变最不发达国家，可以提高莴苣的产量和营养品质。但是，如果明暗时段过长，则会对生菜的生长产生负面影响。此外，在相同的用电量基础上，缩短收获前最不发达国家的产量可提高产量和营养质量。这将对莴苣的生长产生不利影响。此外，在相同的用电量基础上，缩短收获前最不发达国家的时间可提高产量和营养质量。这将对莴苣的生长产生不利影响。此外，在相同的用电量基础上，缩短收获前最不发达国家的时间可提高产量和营养质量。