Electricity + Control April 2019

LIGHTING

The growth of horticultural lighting

By Gregg Cocking, editor, Lighting in Design

Take Note! The properties of LED lighting and advances in our understanding of plants, now provide for light to be tuned to boost yield and maintain plant health in the horticultural industry. The greenhouse use case for LEDs is primarily as a supplementary light source to the sun.

Horticultural lighting is revolutionising the future of farming with technologies and innovations enabling year-round sustainable crop cultivation.

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T he revolution in horticulture is a seismic shift that will fundamentally change how we grow plants – and it’s all down to lighting. Thanks to the properties of LED lighting and ad- vances in our understanding of plants, we are now able to tune light in order to boost yield, customise plant characteristics and maintain plant health. At a basic level, horticulture is relatively simple. Given the right soil, temperature, moisture and lighting conditions, horticulturalists should be able to cultivate plants anywhere. The lighting compo- nent in this formula is much more complex than replacing natural light with an artificial light source. Plants require lights with specific spectral char- acteristics, including concentrations of light with- in the appropriate wavelength bands to facilitate plant photosynthesis. Green plants require great- er amounts of light in blue and red wavelengths, but have other wavelength requirements between those two bands. Before the advent of LED light- ing, horticulturalists were unable to generate artifi- cial light that met all wavelength requirements for optimum plant growth. The use of LEDs The power consumed when converting electric- ity into PAR photons determines the efficiency of the luminaire, and LEDs are the most energy- efficient solution available. In addition to most common top-lighting applications where lumi- naires are placed at ceiling level, LEDs can be used closer to plants because of their lower heat radia- tion. This allows luminaires to be installed much closer to plants to create more dense farms ver- tically. Mixing different colour LEDs allows better matching of the light spectra for each species and the stage of growth of the plant. With LEDs the luminaires also have a longer lifetime and lower maintenance needs.

Optics, on the other hand, help focus the light/ photons onto the plants, allowing either greater crop yield and shorter growing cycles or reduced luminaire bill of materials costs. Having uniform light and spectral distribution also helps to pro- duce healthier and more productive plants. Focus- ing light energy where it is needed gives greater photosynthetic photon flux density (PPFD) with less power. The greenhouse use case for LEDs is primari- ly as a supplementary light source to the sun, al- though artificial lighting is increasingly vital during the colder and shorter days of winter. Cannabis also requires greenhouse-like space where plants can grow vertically. Most legal cannabis growing operations are indoors and require electrical fix- tures as the primary light source. Where LEDs are having the greatest impact, however, is in grow- ing leafy greens and herbs that only reach heights measured in centimetres and that can be grown in layers or racks with each layer having a dedicat- ed set of LED luminaires relatively close to the plants, again enabled by little to no heat radiated by the LEDs. The layering assists so-called urban or vertical farms to occupy relatively small growing spaces inside buildings near population centres, while optimal lighting and technology – including hydroponics – enable faster plant/harvest cycles than can be achieved outdoors. Challenges in horticultural lighting There are, of course, challenges in any emerging technology and perhaps even more so in LED- based horticultural lighting where experience with SSL (solid-state lighting) technology is still shallow. Lighting manufacturers based in Asia have tar- geted the market with what are often affordable but low-end products. However, many of the low-end products on the market lack pertinent certification.

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Horticultural lighting terms Photosynthetic photon flux (PPF): This comes from the total amount of photosynthetically active radiation (PAR) that has the most effect on how strong plant growth will be. More PPF means more photons and more power, and this value is easily measured and used as a parallel to lumens. Photosynthetic photon flux density (PPFD): How many of the photons hit their target, and this can be related to lux levels. Top lighting – Greenhouses: Illumination of the hall and plants from ceiling level. Top lighting – Vertical farming: Illumination from the top of the plants at a close distance. Intra-canopy lighting: Illumination on the side or in- between the plants.

Electricity + Control

APRIL 2019

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