The effects of LED light intensity on lettuce coloration and biomass

Abstract

Light emitting diodes can potentially be a useful tool for lettuce (Lactuca sativa) indoor production because of its ability to control light spectra and provide high light levels with little radiant heat. This study was conducted to test coloration, biomass, and anthocyanin concentration in lettuce grown under different light intensities, giving us insights on how changing light intensities can improve coloration and increase productivity. The experiment was conducted in a laboratory with controlled light, humidity and temperature, eliminating as much variability as possible. The following three treatments were used: (1) standard intensity at 250 µmol/m²/s throughout the growing period, (2) high intensity at 500 µmol/m²/s throughout the growing period, and (3) standard intensity at 250 µmol/m²/s then high intensity of 500 µmol/m²/s two days before harvest. Measurements included subjective visual color ratings, fresh weight biomass, and anthocyanin concentration. There were significant differences among treatments in color ratings and biomass, and no significant differences in anthocyanin concentration. The 250 µmol/m²/s and 250/500 µmol/m²/s treatments showed little differences in color rating. The 500 µmol/m²/s treatment led to higher red pigmentation in plants. The 500 µmol/m²/s treatment was numerically but not significantly higher in biomass than the 250 µmol/m²/s treatment, while the 250/500 µmol/m²/s treatment was lowest. Growers who produce lettuce in a greenhouse setting and are capable of increasing light intensity can apply light intensity at 500 µmol/m²/s throughout the growing season to improve coloration and maintain productivity.