Growing With Added UVA & Far Red

Growing with added UVA and Far Red.

Photosynthetic Active Radiation or PAR refers to the spectrum of electromagnetic radiation that plants can use. Plants use this light energy to drive photosynthesis, grow and reproduce. The spectrum is measured in nanometres (nm) and for many years it was agreed that the range of visible light (PAR) sits between 400nm and 700nm.

At the low end of the PAR range is blue light and at the upper end is red light

Recent plant research states that expanding the spectrum of light outside of the “traditional” PAR range has significant effects on plant behaviour and that the actual usable range is 380nm to 780nm.

The Dio-Tech UVA/Far Red Light Bars does just that. It extends the spectrum to include not only visible light, but also UVA and Far Red, for optimal plant performance.

Electromagnetic radiation with a wavelength between 315nm and 400nm is classed as UVA. This wavelength induces a stress response within the plants, much as it does in humans, to develop compounds that will protect its cells from being damaged by prolonged exposure.

Receiving UVA radiation stimulates the plants natural defences and encourages it to develop thicker, waxier leaves. This helps protect the plant against biotic stress factors, like pests, fungal and bacterial pathogens. Research also suggests that UVA deters certain species of sucking insects.

Most importantly, exposure to UVA during the flowering period stimulates the production of resin, terpene and flavonoid compounds, and increases biomass.

NOTE: We do not use UVB emitting diodes in our fixtures as this wavelength of light can be harmful to both plants and humans unless dosed for short periods of time. UVA can be on all the way during your flowering cycle while your lights are on – it is not restricted to 15 minutes per day, unlike UVB.

Far red or FR is found at the opposite end of the PAR spectrum to UVA, it sits between 700nm and 780nm. It was widely believed that FR on its own stimulated little photosynthetic

activity within the plant and that it was not included in the PAR range. This phenomenon was known as “Far Red Drop” as the rate of photosynthesis significantly drops beyond 700nm.

However, later research by Robert Emerson found that when FR was combined with deep red wavelengths of around 680nm it becomes photosynthetically active and increases the photosynthetic rate beyond what is usually achievable below 700nm. This phenomenon is known as The Emerson Effect.

This “stacking” of usable light significantly increases biomass and flower production.

FR penetrates the leaf canopy more deeply than blue, green or red, so much so that exposure to FR triggers a shade aversion response stimulating stem elongation and flower development in plants as they try to outgrow and compete against the plants that are shading them. It is for this reason that we recommend only using the UVA/FR Light Bars during flowering.