Red light is the basal component in lighting spectra. Sole red light is sufficient for normal plant growth and photosynthesis. Different wavelengths of red light might have uneven effects on plants. Lettuce biomass yield increased when the wavelength of the red LED emitted light increased from 660 to 690 nm. It is suggested for growers to use ~640 nm or ~660 nm red LEDs for the cultivation of lettuce and other green vegetables. Red LED light had no remarkable positive effect on growth and development of plants, but activated the action of the antioxidant system. 660 nm LED light, applied as a sole light source in the controlled environment stimulated anthocyanin accumulation in red leaf cabbages as compared to blue or green LED wavelengths. 658 nm red light supplemental for cool white fluorescent lamps resulted in higher phenolics concentration in baby leaf lettuce. Short term pre-harvest treatment with red 640 nm LEDs in controlled environment resulted in enhanced lutein and glucosinolate sinigrin accumulation in red-leaf cabbages.
The results of series of experiments, performed with 638 nm LED light (supplemental for natural and HPS illumination) pre-harvest treatment in greenhouses presents the increased antioxidant capacity, enhanced contents of phenolic compounds and alpha-tocopherol as well as reduced nitrate contents in different lettuce varieties and other leafy vegetables. Red light enhanced tomato yield.
Plants reproductive growth benefited from it. It reduced nitrate content in lettuce, green onions, red and green leaf lettuce, in dill and parsley.
The additional red light increased vitamin C content in mustard, spinach, rocket, dill and onion. Red light is among the best colours of light to stimulate plant growth. The pigment phytochrome mediates flowering of plants with a photoperiodic flowering response. Generally, plants are very sensitive to low intensities of red light; during the night low amounts of red light can inhibit flowering of short-day plants and promote flowering of some long-day plants because of phytochrome’s sensitivity to red light.