Effects of Far-red and Red-enriched Lights on the Quality Attributes of Indoor Lettuce

Abstract The increasing demand for leafy greens shifted their year-round production towards indoor systems. In order to be marketable leafy greens, such as lettuce, must be visually attractive and provide high nutritional value and health benefits. These quality attributes depend on various light-driven processes, including physiological performance, metabolism, growth and the characteristics of the cultivar, among other factors. In our research, we analyzed the quality attributes (e.g., growth, firmness, element and pigment contents, antioxidant capacity) of two looseleaf lettuce ( Lactuca sativa L.) cultivars, green and red leaf lettuce grown under far-red (1st experiment) and red- (2nd experiment) enriched artificial LED lighting. Unlike other studies, we not only considered the preset LED- and cultivar-wise plant groups but also those created by a K-means clustering algorithm. Hereby, we assessed the preset conditions and captured more subtle differences that would otherwise be masked by the natural variation in the plants’ performances. We found that an increased ratio of far-red and red photons in the light recipe may enhance lettuce growth but with significant variability related to other quality attributes that may accompany the growth and development of the plants. In some cases, there was a trade-off between growth and other quality attributes, while in other cases, these two changed in parallel because of the characteristics of the cultivar. We also observed that both red and far-red light enrichment conditions increased axillary pigment production in lettuce providing superior nutritional quality.