The 2012 ASHS Annual Conference

There is growing concern about food safety, environmental impact, and efficient energy usage in agricultural production systems. Producing lettuce under artificial lighting can be a solution addressing these concerns. Light-emitting diodes (LEDs) offer the advantage of a narrow light spectrum, low power consumption, and little heat production. The objective of this study was to determine the effects of different light sources on the growth of miniature 'Tom Thumb' butterhead lettuce in a noncirculating hydroponic system. Lettuce seedlings were started in Oasis cubes, which were transferred to net pots in 1.9-liter containers containing a hydroponic nutrient solution. The solution was Hydro-Gardens' Chem-Grow Lettuce Formula 8-15-36 hydroponic fertilizer with added calcium nitrate (15.5%-0-0) and magnesium sulfate (9.8% Mg). The lettuce was grown in a lab under different light treatments—blue LEDs, red LEDs, and high output fluorescent lights. The light level was 58.9 μmoles/m²/s with an air temperature 21.9°C. At the end of the study, the pH of the nutrient solution of the blue LED and the fluorescent light treatments were greater than the red LED treatment. Electrical conductivity of the nutrient solution of the fluorescent light treatment was greater than the blue LED treatment and the red LED treatment. Fluorescent lights resulted in greater root dry weight than blue LEDs and red LEDs. Total plant dry weight under fluorescent lights was greater than under red LEDs. There were no significant differences in shoot dry weight and plant height among the treatments. Percent partitioning of dry weight to shoots was greatest with red LEDs, followed by blue LEDS, and fluorescent lights. Percent partitioning of dry weight to roots was greatest with fluorescent lights, followed by blue LEDS, and red LEDs. Leaf chlorophyll content was greater under blue LEDs and fluorescent lights than red LEDs. In conclusion, LEDs can provide an alternative lighting source for miniature lettuce.