The effect of artificial light technologies on balancing red pigmentation and yield in red winter lettuce

Abstract:

The study explored the effects of artificial light on growth, pigmentation, and energy efficiency in red winter lettuce grown in controlled environments, addressing the challenge of low natural light in northern regions and the trade-off between lettuce yield and pigmentation. Two greenhouse experiments compared HPS lamps, LEDs, and a Hybrid system combining HPS and LEDs. The study evaluated red winter lettuce growth, quantified leaf color using the RGB color model, and assessed energy-use efficiency. Since the greenhouse was heated with geothermal energy, the energy-use efficiency was defined as the ratio of the plant’s fresh weight to the energy consumed by the lights. Lettuce grown under LEDs with higher PPFD (167 µmol m^-2 s^-1) and day temperatures (20 °C) showed enhanced red pigmentation compared to HPS lighting (132 µmol m^-2 s^-1, 19 °C) but at the cost of lower fresh weight. Hybrid systems significantly improved pigmentation compared to HPS, although coloration remained below the desired threshold. LEDs reduced energy use by 37% compared to HPS while offering superior energy efficiency. Hybrid systems cut energy costs by 9% but did not improve energy efficiency. The findings highlight the importance of balanced lighting strategies to optimize pigmentation and energy efficiency while maintaining plant growth. This study provides new insights into identifying optimal lighting strategies, while simultaneously considering temperature settings, to achieve a balance between growth and pigmentation in lettuce cultivated under controlled environment agriculture.

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