Effect of LED interlighting combined with overhead HPS light on fruit yield and quality of year-round sweet pepper in commercial greenhouse

Inter-lighting, applying supplemental light within crop canopy, has been shown to improve plant vertical light distribution and light use efficiency, with high-pressure sodium (HPS) lamps. However, it is not feasible on vegetables cultivated with the popular twin-row system (narrow row) used in major greenhouse vegetable production area in northern regions because of its high bulb temperature. Light-emitting diodes (LEDs) has low operating temperature and thus is potentially a good fit for inter-lighting. In this study, therefore, the effects of LED inter-lighting on sweet pepper growth, fruit yield and quality, and light and energy use efficiency were investigated in the commercial greenhouse. To optimize the production system with LED inter-lighting, different levels of top HPS lighting were also evaluated in the two experiments. Experiment one evaluated single row of LED inter-lighting module per twin-row (56.8 µmol m-2 s-1) without or with top HPS (78 µmol m-2 s-1). Experiment two evaluated the same LED inter-lighting module without or with the top HPS lamps at greater light intensity (155 µmol m-2 s-1). LED inter-lighting improved plant growth, fruit yield and quality compared to the top HPS treatment. Moreover, LED inter-lighting significantly increased fruit dry matter content and the content of health promoting compounds in fruits, including total phenolic content, total carotenoid content and antioxidant activities (ferric reducing antioxidant power assay and 2, 2-diphenyl-1-picrylhydrazyl assay), compared with the HPS treatments. As a result of LED inter-lighting more light reached the crop canopy with a higher efficiency of electricity to light conversion and the plants grown with LED inter-lighting and top HPS achieved higher yield and quality than that with the top HPS only in both experiments.