Do plants need sleep? Dynamic 24 h lighting for greenhouse production of tomato, pepper, and cucumber

Continuous lighting (CL) supplemented during greenhouse production has the potential to improve resource-use-efficiency by reducing the initial fixtures needed and to lower electrical costs in some regions of the world. However, many crop types have been shown to develop leaf injury characterized by chlorosis and reduced photosynthetic rates leading to no further increase in yield or reduced yield. Here we assess the current understanding and limitations of CL plant production including the use of dynamic CL (changes in photosynthetic photon flux density (PPFD) and/or spectrum between the day and night) vs. static CL (i.e., constant PPFD and spectrum for 24 h) as a potential strategy to reduce the prevalence of CL-injury in sensitive crops. We discuss the genotypic response of plants to CL and the need to identify breeding lines/cultivars which are more tolerant to extended photoperiods. We also discuss the impact of CL and the potential for the use of by-product heat from the lighting application to supplement the greenhouse heating requirements during the nighttime period.