Light Source Effects on Hydroponically Grown Miniature 'Pom Pom' Lettuce

There is growing concern about food safety, environmental impact, and efficient energy usage in horticultural production systems. Producing lettuce under artificial lighting can be a solution addressing these concerns. Light-emitting diodes (LED) offer the advantages of a narrow light spectrum, low power consumption, and little heat production. Light emitting plasma (LEP) provides high light intensity, sun-like full spectrum, and long life. The objective of this study was to determine the effects of different light sources on the growth of miniature 'Pom Pom' loose-leaf lettuce in a noncirculating hydroponic system. Lettuce seedlings were started in Oasis cubes, which were transferred to 5.1-cm net pots and put in 1.9-liter containers containing a hydroponic nutrient solution. The solution was composed of Hydro-Gardens' Hobby Formula 10-8-22 hydroponic fertilizer with added magnesium sulfate (9.8% Mg). The lettuce was grown in a lab under different light treatments—red+blue+white LEDs, light emitting plasma, and high output T-5 fluorescent lights (HO). The light level was 261 µmoles/m²/s with an air temperature 21°C. At the end of the study, plants were taller under the LEP and HO treatments than the LED treatment. The HO treatment resulted in greater partitioning of dry weight to the shoots than the LED and LEP treatments. Under the LED and LEP treatments, a greater partitioning of dry weight to the roots and a greater root-shoot ratio occurred compared to the HO treatment. SPAD readings were highest for the LED treatment. The LED treatment also produced the greatest shoot dry matter production per unit amount of nutrient solution used than the other two treatments. The LED treatment used the least amount of nutrient solution for lettuce production. The electrical conductivity of the remaining nutrient solution of the HO treatment was the highest, followed by the LEP treatment and the LED treatment. There were no significant differences in shoot dry weight, root dry weight, total plant dry weight, and the pH of the remaining nutrient solution in the containers. In conclusion, LED and LEP lights may provide alternative lighting sources to fluorescent lights for miniature lettuce.