In the life cycle of plants, most developmental processes are dependent on light. Significant biological processes, such as germination, shade avoidance, circadian rhythms and flower induction, are all affected by light. Recent advancements in the use of light-emitting diode (LED) lighting in plant and vegetable production systems has researchers looking for insights into the effects of these artificial lights on the growth and yield of crops. Scientists from the Department of Horticultural Science at Chungbuk National University published a study entitled “Leaf Shape, Growth, and Antioxidant Phenolic Compounds of Two Lettuce Cultivars Grown under Various Combinations of Blue and Red Light-emitting Diodes” by Ki-Ho Son and Myung-Min Oh in HortScience that reveals the advantages and challenges of LEDs in lettuce cultivation.
The increased use of LEDs in environmentally controlled closed-type plant production systems allows crop production throughout the year, regardless of external weather conditions. According to the authors, LEDs have some advantages over traditional lighting sources in plant cultivation (i.e., high light-conversion efficiency with low radiant heat output, semi-permanence and small mass, as well as a variety of narrow wavebands to improve both crop yield and quality). The authors explained that blue and red LEDs are typically used for plant growth because Chlorophyll A and Chlorophyll B efficiently absorb wavelengths in the blue and red ranges.
The research design used red and green leaf lettuce subjected to six LED lighting treatments. The scientists examined growth characteristics including the fresh and dry weights of shoots and roots, shoot-to-root ratio, total leaf area and chlorophyll content. Chlorophyll fluorescence, antioxidant capacity, phenolic concentration and flavonoid concentration were also measured in the study.
The experiments confirmed that both blue and red LEDs have a positive effect on the accumulation of antioxidant phenolic compounds and lettuce growth, respectively. According to the scientists, red light irradiation without blue light was effective at stimulating the biomass accumulation of lettuce plants; however, red light alone induced abnormal leaf shape and had a negative effect on polyphenolics and antioxidant levels. They recommended a mixture of blue and red LEDs to enhance lettuce crop quality and yield in closed-type plant production systems.