Experiments were conducted in a vertical growing system on two lettuce varieties (Red Oakleaf and Green Butter Salanova) under three different light treatments – fluorescent T5 light bars, Illumitex F3 LEDs, and Illumitex X5 LEDs. Environmental parameters and light-source wattages were identical for the three light treatments. Due to differences in light fixture efficiencies, the LED light sources produced up to 5.3 times the number of photons within the photosynthetically active radiation (PAR) wavelength range of 400-700nm. The growth of red and green lettuce under LEDs increased significantly over the fluorescent light, with the red lettuce increasing more (287-314%) than the green lettuce (173-219%). Blind taste-testing found LED grown lettuce to be preferred in terms of appearance and taste, and to be less bitter than the fluorescent grown lettuce. The results of this study suggest that on a watt-to-watt basis, growers using vertical farming systems growing lettuce are best served to use LED light sources over fluorescent light for improved biomass, productivity, and marketability.
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