Importance of light source position in exposure sequence for optimization of coloration and yield of red winter lettuce

Abstract

Winter production of greenhouse crops in northern countries is totally dependent on supplementary lighting. The aim of this study was to investigate the effect of the light source (high-pressure vapor lamps (HPS), light-emitting diodes (LED), or a combination) and their distribution in time on growth and coloration of red winter lettuce (Lactuca sativa L. cv. ‘Carmoli’). The used energy associated to each of the light treatments was also evaluated. The number of leaves, fresh and dry weight were significantly higher for plants treated only with HPS lights, whereas the red pigmentation was enhanced in plants grown only under LEDs. The lower yield under LEDs was associated with a significantly lower leaf temperature compared to plants grown under HPS lights. One week at the end of the growth period under LEDs was enough to achieve a satisfactory red color, while not compromising plant yield. The energy use efficiency was increased by nearly 50% in the LED-only treatment despite the lower plant yield compared to the HPS-only treatment. These results demonstrate that supplemental light quality can be strategically used by improving the light source position in exposure sequence to enhance the growth and coloration of winter lettuce.