Effect of Interchanging Red and Blue LED Irradiation Sequence on Growth of Lettuce

Abstract

Light-emitting diode (LED) is commonly employed as supplementary light sources to enhance plant growth and quality. Nowadays, a combination of red (R) and blue (B) LED sources is mainly used since it can boost plant photosynthesis rate and biomass. Generally, both light sources are continuously irradiated for 16–18 hours for plant photoperiod, which may result in high electricity costs. Therefore, interchanging use of red and blue LED irradiation is introduced to reduce the use of electricity, thus minimising the operating cost. In this study, a growth chamber with red and blue LED was constructed and its intensity and power distribution were assessed. The effect of blue and red LED irradiation sequence on plant growth parameters and chlorophyll content was examined. Three light treatments over a period of 16 hours (RB16 - 16 hours constant simultaneous (R) and (B) light, R4/B4 - 4 hours interval interchanging R and B light and R8/B8 - 8 hours interval interchanging R- and B-light) were exposed to lettuce under controlled room temperature. Results revealed that the different light treatments influence lettuce plant morphology such as plant height, leaf width and leaf number. However, the results are similar for fresh and dry mass, and chlorophyll concentration. It is found that, both plant height and leaf width were the highest under R4/B4 and RB16, respectively. Such findings would be extremely valuable information on the use of interchanging LED irradiation in plant development for commercial production, resulting in optimized power consumption.