Ultraviolet (UV)
Ultraviolet (UV) light falls outside the visible light range, or PAR, between 100 and 400 nanometers. This type of light can be divided into UV-A, UV-B, and UV-C.
UVA lies between 320 – 400 nm and is also called Near UV
UVB lies between 290 – 320 nm and is also called Middle UV
UVC lies between 100 – 290 nm and is also called Far UV
The correct implementation of Ultraviolet light can have many benefits. Fighting diseases (such as Mildew) and better smelling and tasting produce are among the benefits of UV light. UV light will help initiate and strengthen a plant’s physical and chemical defense mechanisms and antioxidants including terpenoids, alkaloids, lycopene, anthocyanins, trichomes, phenols, quinones, carotenoids, beta-carotene, and glycosides. These compounds protect your plants since most of them are toxic to insects and disruptive to the DNA of microorganisms found in molds, pathogens, bacteria, and viruses. These antioxidants also influence the physical and nutritional value of plants, making plants more colorful, and taste and smell better! Treating plants with UV light correctly can prevent fungal diseases such as Botrytis (Gray Mold) and Powdery Mildew from further spreading and surviving by up to 99%1, 2.
Far-Red
Plants can respond to different colors of light by changing their growth form (phytomorphology). Plants sense increased amounts of Far Red (705-740nm) and interpret the high amounts as being in the shadows. This can lead to plants stretching excessively.
Shade Avoidance Syndrome
Excessive shade and Far Red light can lead to plants developing a “shade avoidance syndrome”. The plant will then display a set of responses, usually including elongation, early flowering, and increased apical dominance. A plant in the shades may also think the risk of death is too high and start flowering earlier and even increase its number of flowers to reproduce and pass its genetics on.
Emerson Effect
Exposing a plant to a combination of Deep-Red and Far-Red light can give a 30% higher photosynthesis rate than the sum of the Deep-Red light and Far-Red light photosynthesis rates. This effect is known as the Emerson effect.
2 Suthaparan, A. et al. Suppression of Powdery Mildews by UV-B: Application Frequency and Timing, Dose, Reflectance, and Automation. Plant Dis. 100, 1643–1650 (2016).