Transplant lettuce response to different blue:red photon flux ratios in indoor LED sole-source lighting production
As indoor growing systems play an increasing role in transplant crop production, light optimization must be developed to increase plant growth, improve morphology, and reduce electrical energy costs. Light emitting diodes (LEDs) are an increasingly used technology for the production of transplants. The objective of this experiment was to evaluate the effects of different blue (B) and red (R) photon flux (PF) ratios for the production of 'Red Oakleaf' and 'Green Oakleaf' lettuce (Lactuca sativa L.) transplants. Plants were grown for 16 days with LEDs in a light-quality growth chamber with 78.7±1.4% relative humidity, 19.6±1.2°C, and 812±268 µmol mol-1 CO2. Five LED light treatments consisted of different percentages of B (peak: 452 nm) and R (peak: 659 nm) PF: 0B:100R, 20B:80R, 50B:50R, 80B:20R, and 100B:0R. A fluorescent treatment was used as a control. Plants were provided with 200 µmol m-2 s-1 photosynthetically active radiation (400-700 nm) for 18 h. Transplants under 20B:80R had greater shoot dry mass than plants under all other LED treatments. For example, transplant lettuces under 20B:80R had 15% more shoot dry mass than those under the 50B:50R LED light treatment. Transplant lettuces under 100B:0R had on average 19% fewer leaves than plants in all other treatments. This preliminary study demonstrates that 20B:80R PF is the preferred light quality for the production of lettuce transplants in indoor growing systems.
Spalholz, H. and Hernández, R. (2018). Transplant lettuce response to different blue:red photon flux ratios in indoor LED sole-source lighting production. Acta Hortic. 1227, 555-562
red/blue light ratio, light emitting diode, sole-source lighting, Lactuca sativa