Sparks Electrical News September 2022

LIGHTING

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Far-red: The light which plays an important role in plant growth I n the last issue of Sparks Electrical News , InDorSun and Giant light introduced us to the fascinating world of lighting for can nabis growth. We would suggest you read the article, but here is a quick summary: increasing photochemical efficiency than photons below 703 nm or above 731 nm FR. Photons of wavelength above 752 nm are not effective in enhancing photochemical efficiency as they are no longer used by the first photosystem due to low photon energy and absorption.

Light spectrum is the range of wavelengths produced by a light source. When discussing light spectrum, the term ‘light’ refers to the visible wavelengths of the electromagnetic spectrum that humans can see from 380–740 nanometers (nm). Ultraviolet (100–400 nm), far-red (700–850 nm), and infra-red (700–106 nm) wavelengths are referred to as radiation. Growers are most interested in the wavelengths that are rel evant to plants. Plants detect wavelengths that include ultraviolet radiation (260–380 nm) and the visible portion of the spectrum (380–740 nm) which includes PAR (400–700 nm), and far-red radiation (700–850 nm).

Far-red light increases the ability of plants to capture light Plants use light not only as a source of energy (i.e., in the process of photosynthesis), but also for information about the surrounding environment.

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Here are a few of the abbreviations we learned: • Photosynthetically active radiation (PAR) is represented as 400-700 nanometers (nm) • Photosynthetic photon flux (PPF) is measured in micromoles per second (μmol·s-1) • Photosynthetic photon flux density (PPFD) is measured in micromoles per square meter per second (μmol·m-2·s-1) • Daily light integral (DLI) is measured in moles per square meter per day (mol·m−2·d−1) • Photosynthetic photon efficacy (PPE) is measured in micromoles per joule (μmol·J-1) Far-red light and photosynthesis Far-red (FR) light is a waveband at the extreme end of the visible light spectrum. It is regarded as wavelengths between 700 and 780 nanometers (nm). To human eyes, FR is only dimly visible, but it plays a very important biological role for plant growth and yield. FR has long been considered to have a minimal input in photosynthesis and is excluded from the definition of Photosynthetically Active Radiation (PAR; 400 to 700 nm). It is because the photo synthetic efficiency of monochromatic FR light sharply declines with the wavelength. FR is largely reflected and transmitted by plant leaves, and only about 30% is absorbed. Several recent studies have shown that far-red photons interact with shorter wavelength photons to increase efficiency of photosynthesis. Zhen and Bugbee (2020) have studied the effect of FR on whole plant photosynthesis for 14 different crop species. They concluded that adding far-red pho tons to a spectrum of shorter wavelengths (e.g., broad white spectrum) caused an increase in canopy photosynthesis equal to adding additional light from PAR range (400-700 nm) of the same intensity. The effect was wavelength dependent. The authors postulated that radiation between 700 and 750 nm should be included in the defini tion of Photosynthetically Active Radiation (PAR). InDorSun offers the majority of its fixtures with separate control of the FR circuit. This enables the grower to use FR as a tool, either on its own or with broad spectrum white light. How does it work The phenomenon is not new and is known as the Emerson effect. Robert Emerson (1957) found out that plants exposed simultaneously to light of shorter and longer wavelengths then 680 nm, have much more efficient photosynthesis than if they are exposed to only shorter or longer wave lengths separately. It happens because photo synthesis is driven by two photosystems which work in synergy. It can be compared to two pump mechanisms used to transport energy. The first pump or photosystem uses red photons to pump up electrons on a higher level. The second pump or photosystem uses far-red photons to pump up electrons even further. High energy photons are used to synthetize basic building biochemicals which can be used to make different substances e.g. sugars. The efficiency of the system is high est when both pumps work together in a balanced way. Using laser diodes to obtain extremely narrow wavebands, Zhen et al. (2018) found that photons from 703 to 731 nm tended to be more efficient at

SPARKS ELECTRICAL NEWS

SEPTEMBER 2022