The economic viability and energy use of vertical farms strongly depend on the efficiency of the use of light. Increasing far-red radiation (FR, 700–800 nm) relative to photosynthetically active radiation (PAR, 400–700 nm) may induce shade avoidance responses including stem elongation and leaf expansion, which would benefit light interception, and FR might even be photosynthetically active when used in combination with PAR. The aims of this study are to investigate the interaction between FR and planting density and to quantify the underlying components of the FR effects on growth. Lettuce (Lactuca sativa cv. Expertise RZ) was grown in a climate chamber under two FR treatments (0 or 52 μmol m^–2 s^–1) and three planting densities (23, 37, and 51 plants m^–2). PAR of 89% red and 11% blue was kept at 218 μmol m^–2 s^–1. Adding FR increased plant dry weight after 4 weeks by 46–77% (largest effect at lowest planting density) and leaf area by 58–75% (largest effect at middle planting density). Radiation use efficiency (RUE: plant dry weight per unit of incident radiation, 400–800 nm) increased by 17–42% and incident light use efficiency (LUE_inc: plant dry weight per unit of incident PAR, 400–700 nm) increased by 46–77% by adding FR; the largest FR effects were observed at the lowest planting density. Intercepted light use efficiency (LUE_int: plant dry weight per unit of intercepted PAR) increased by adding FR (8–23%). Neither specific leaf area nor net leaf photosynthetic rate was influenced by FR. We conclude that supplemental FR increased plant biomass production mainly by faster leaf area expansion, which increased light interception. The effects of FR on plant dry weight are stronger at low than at high planting density. Additionally, an increased LUE_int may contribute to the increased biomass production.

垂直农场的经济可行性和能源使用在很大程度上取决于光的使用效率。相对于光合有效辐射（PAR，400-700 nm），增加远红外辐射（FR，700-800 nm）可能会引起避光反应，包括茎伸长和叶片扩张，这将有利于光的截获，并且FR甚至可能是光合作用的与PAR结合使用时有效。这项研究的目的是调查FR与种植密度之间的相互作用，并量化FR对生长的潜在影响。生菜 （紫花苜蓿简历。在两个FR处理（0或52μmolm ^–2 s ^–1）和三种种植密度（23、37和51个植物m ^–2）下，将专业知识RZ种植在气候箱中。89％的红色和11％的蓝色的PAR保持在218μmolm ^–2 s ^–1。添加FR使4周后的植物干重增加46-77％（在最低种植密度下效果最大），叶面积增加58-75％（在中等种植密度下效果最大）。辐射利用效率（RUE：每单位入射辐射的植物干重，400–800 nm）增加了17–42％，入射光利用效率（LUE _inc：通过添加FR，单位入射PAR（400-700 nm）的植物干重增加了46-77％；在最低种植密度下观察到最大的FR效应。通过添加FR（8–23％），拦截光的利用效率（LUE _int：单位截获的PAR的植物干重）增加。FR既不影响特定叶面积也不影响叶片净光合速率。我们得出的结论是，补充FR主要通过更快的叶面积扩展来增加植物的生物量产量，从而增加光的拦截。FR对植物干重的影响在低种植时比在高种植密度时要强。另外，增加的LUE _int可能有助于增加生物量的产量。