Light-Emitting Diodes (LEDs) Therapy

A novel research of pulsed LED lighting versus continuous lighting was conducted by analyzing phytochemicals levels in microgreens. Red pak choi (Brassica rapa var. chinensis), mustard (Brassica juncea L.) and tatsoi (Brassica rapa var. rosularis) were grown indoors under HPS lamps supplemented with monochromatic (455 nm, 470 nm, 505 nm, 590 nm and 627 nm) LEDs (total PPFD 200±10 µmol m(-2) s(-1); 16 h day(-1)). For pulsed light treatments, the frequencies at 2 Hz, 32 Hz, 256 Hz, and 1024 Hz with a duty cycle of 50% of monochromatic LEDs were applied. The results were compared with those under the continuous light (0 Hz) condition in terms of total phenolic content, anthocyanins and antiradical activity (DPPH). The summarize data suggested that pulsed light affected accumulation of secondary metabolites both positive and negative in microgreens. The significant differences in the response of phytochemicals between pulsed light at several frequencies and continuous light were determined. The most positive effects of 2 Hz, 256 Hz, 1024 Hz for total phenolic compounds in mustard under all wavelengths LEDs were achieved. The LEDs frequencies at 2 Hz and 32 Hz were the most suitable for accumulation of anthocyanins in red pak choi and tatsoi. The highest antiradical activity under the treatments of 32 Hz, 256 Hz and 1024 Hz in mustard, and under the 2 Hz frequency in red pak choi and tatsoi was determined.