2017 ASHS Annual Conference

Light Emitting Diodes proposed for use in horticulture can be direct emission LEDs (individual colors) or blue LEDs that are down converted to white through the use of a variety of different phosphors. Biomass, anthocyanin, carotenoid and chlorophyll concentrations as well as photochemical analyses were performed on red lettuce Rouxai grown under LED light sources using four different phosphor combinations and a direct RBG emission fixture in environment controlled growth chambers. Previous work indicated significant differences in plant biomass and pigment concentrations in leafy greens grown under phosphor converted LEDs but the spectral ratios between the different light sources were different, therefore the effects could not be attributed to phosphor conversion or spectral ratios. The LED fixtures used in this study were specifically designed to give identical PFDs and RBG spectral ratios in LED fixtures using different phosphor combinations. The red lettuce plants grown under all light treatments were able to utilize the absorbed light in photochemistry equally well as the effective and maximum quantum yields were similar as were nonphotochemical and photochemical quenching as determined through chlorophyll fluorescence measurements. Similar findings were observed for total carotenoid concentrations under the different light treatments. However, fresh weights, anthocyanin and chlorophyll concentrations were significantly different between the different phosphor converted and direct emission LEDs. Detailed spectral analyses and their resultant biological effects on red lettuce Rouxai will be discussed.