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The Physiology, Growth and Essential Oil Content of Lemon Balm (Melissa officinalis L.) in Response to Different LED Treatments

Background: Light-emitting diodes (LEDs) are a promising technology that has enormous potential to improve irradiance efficiency and to replace traditionally used horticultural lighting. Compared with traditional light sources (e.g., high-pressure sodium lamps and metal halide lamps) used in crop production, LEDs tends to have long life, generate less heat waste and providing the perfect spectrum for plant growth.
Methods: This work sought to investigate the effect of using blue LED lights on growth and development in Lemon balm (Melissa officinalis L.) under sole-source LED lighting spectra. Lighting spectra were provided by differing combinations of LEDs of 4 different peak wavelengths, (Blue 435, Blue 450, Red 663 nm and Green 540 nm) with ratios of (1.95:2.3:1 R: G: B 450 nm (white), 5: 1R: B 450 nm, 2.5:1 R: B 450 nm and 2.5:1 R: B 435 nm) at a PPFD of 95 ìmol m-2 s-1 (PAR). Result: showed that the blue light with a wavelength peak at 435 nm in combination with red light at 663 nm at the ratio of (2.5:1 R: B) and white LEDs enhanced the physiology of lemon balm (i.e., significantly increased assimilation rate, stomatal conductance and transpiration rate), consequently fresh and dry shoot weight increased and the shoot essential oil content.
