2019 ASHS Annual Conference

Light emitting diode (LED) lights are preferred in indoor farms due to their low thermal emission, which enables them to be placed close to plants and at multiple levels. In commercial LED lights, broadband light is produced from blue LEDs using ‘phosphor conversion’ method. A higher proportion of blue light in the total light can be stressful to plants due to excess energy of a blue photon than that is needed for photosynthesis. Lowering blue light fraction and increasing the fraction of lower energy wavelengths (e.g., red light) can increase energy consumption due to increased thermal dissipation by phosphor. Moreover, a higher proportion of blue light can increase carotenoid levels in leaves, a pigment with known health benefits to humans. Our objective was to study the effect of high percentage of red light, blue light and blue light with far-red light in the total light on lettuce growth, energy consumption, energy- use-efficiency (EUE, crop growth per unit energy consumed), crop quality and carotenoid levels in plants. An experiment was conducted using green and red leaf lettuce (Lactuca sativa L.) varieties under three LED treatments containing red (R): blue (B): far red (FR) proportions of R₉₀:B₁₀:FR₀, R₅₀:B₅₀:FR₀, and R₄₃:B₄₃:FR₁₄, each with a total photosynthetic photon flux density of 125 µmol·m^-2·s^-1 under continuous lighting (10.8 mol·m^-2·d^-1). Results indicated that crop growth and energy consumption were lowest in R₅₀:B₅₀:FR_0. However, crop growth significantly increased with far-red addition without differences in energy consumption. Crop growth and energy consumption were highest in R₉₀:B₁₀:FR₀. The presentation will describe bases for observed differences in crop growth, energy consumption, EUE and carotenoid levels among different treatments with recommendations for spectral composition of LED lights for improved EUE and nutritive quality in indoor production.