Analysis of Targeted Supplemental-Waveband Lighting to Increase Yield and Quality of Lettuce Grown Indoors

Lighting from light-emitting diodes (LEDs) is one of the largest capital and operational expenses for indoor farms. While broad-waveband white LEDs are relatively inexpensive, their efficacy is lower than most narrow-band LEDs. This study aimed to determine how supplementing warm-white light with additional blue (400-499 nm), green (500-599 nm), red (600-699 nm), or far-red (700-750 nm) light influences lettuce (<i>Lactuca sativa</i>) growth and quality, and whether these effects are consistent across two photon flux densities (PFDs). We grew lettuce 'Rouxai' and 'Rex' under 90 or 180 µmol∙m^-2∙s^-1 of warm-white light supplemented with 40 or 80 µmol∙m^-2∙s^-1 of blue, green, red, far-red, or warm-white light. Supplemental far-red light increased biomass without reducing secondary metabolites. Supplemental red, far-red, and warm-white light maximized biomass, whereas additional blue light enhanced secondary metabolite concentrations and leaf coloration. Increasing the PFD increased biomass and phenolic content in 'Rouxai'. Notably, spectral effects were consistent across PFD levels, suggesting that higher PFDs do not diminish spectral responses. These results demonstrate the potential of enriching white light to increase yield or quality in controlled-environment agriculture and provide insights for cost-effective commercial production.