2018 ASHS Annual Conference

With ever-improving energy efficiency and decreasing light fixture costs, light-emitting diodes (LEDs) are becoming a promising new light source for greenhouse vegetable production. However, significant questions remain on the best light quality or spectral compositions for greenhouse fruiting vegetable (such as tomatoes, cucumbers and sweet peppers) production. Greenhouse fruiting vegetables are of tall crop, with most of leaf growth occuring in the top and middle canopy while fruit growth in the middle and bottom canopy, and these different growth processes may require different light spectra. LEDs can be used both as top lighting (above the crop canopy) and intra-canopy lighting because of their low surface temperature. Therefore, the light spectrum or spectral compositions of top and intra-canopy LEDs can be optimized for both leaf/vegetative and fruit growth. This study was conducted from Oct. to May in a large greenhouse (200 m²) to compare different spectral compositions of LED top lighting and intra-canopy lighting for greenhouse sweet pepper production. The greenhouse was divided into 4 sections (50m²/section) so that 2 different top light spectral compositions (100% Red or Mixed (red:blue:white = 76:16:8), at the same 140µmol m^-2 s^-1) could be applied with 2 replications. Four intra-canopy light spectral compositions (Control - no intra-canopy lighting, Red (660nm), Blue (455nm) and White at the same 30µmol m^-2 s^-1) were applied to the 4 plots inside each section. Therefore, a total of 8 vertical light spectral compositions/regimes were evaluated in the experiment. The light compositions/regimes resulted in significant difference in leaf photosynthesis, F_v/F_m, plant productivity (total fruit fresh weight and fruit size), and fruit anti-oxidant contents. Therefore, this study has clearly demonstrated that optimized light compositions/regimes should be and can be developed for improving plant growth and fruit yield & quality in greenhouse sweet pepper production with LED supplemental lighting.