LEDs grow greener veg
05 October 2016
LED greenhouse lighting can contribute to reducing food costs, increasing yields and significantly reducing the carbon footprint of our fresh produce.
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According to market research, the worldwide LED grow light market is expected to reach $41.9bn by 2020, growing at a CAGR of nearly 27% between 2015 and 2020. Europe accounts for the major share currently, followed by North America, while Asia is expected to exhibit the fastest growth and eventually move into 2nd place.
This is not simply a replacement market for existing commercial growers. The advantages of LED lighting in horticulture, combined with increasing demand to feed growing populations, falling installation costs and faster return on investment, are stimulating a rapid expansion in greenhouse and indoor farming worldwide.
Replacing traditional lighting with energy-efficient LED lighting in greenhouses has been widely shown to cut electricity usage dramatically. Cost benefit analysis of farmers that have replaced HID and fluorescent lighting with LEDs are showing savings from 40 to 75% on energy alone. Not only do LEDs use considerably less energy, but less heat is also generated, allowing growers to supplement natural light in a sustainable manner, reducing water evaporation and therefore saving on water consumption and cooling. Indeed, in areas where water is at a premium, cultivation under LEDs can require just 20% of the water needed to grow produce outside.
Further, LED fixtures can be placed closer to the plants, allowing multilayer cultivation (vertical farming), as well as enabling inter-lighting for taller plants like tomatoes. Commercial greenhouse operations are able to extend their growing seasons, producing multiple crops in the year, and importantly for consumers, supplying fruit and vegetables locally out of season.
From a government perspective, a critical advantage to sustainable greenhouse and indoor farm cultivation is that by increasing food production locally, and closer to population centres, the burden of transporting food by road or air is significantly reduced, thereby saving on C02 emissions and making LED lighting a truly greener solution. From a consumer standpoint, local production can also avoid the problems of transported food that is often cropped too early, affecting the flavour or texture, or sprayed with chemicals to delay ripening or as a preservative.
However, LEDs can also increase crop yields and improve quality compared to traditional lighting sources. Research has found that photosynthesis in plants depends on absorbing light energy in specific wavelengths. Chlorophyll absorption in plants peaks during exposure to red and blue segments of the light spectrum. Other lighting technologies, such as high pressure sodium and metal halide, do not provide the photons in the appropriate chlorophyll absorption peaks, and waste energy by producing radiation in bands that have no benefit. Fluorescent lamps are better, but still only provide a small percentage of the spectrum required.
The ability to select and tune the spectral output of LED lighting fixtures enables greenhouse growers to supplement natural sunlight, and indoor farmers to generate all the light required for optimal plant growth. Further studies have narrowed down the differing spectrum requirements to optimise for seed germination, root growth, stem growth, flowering and ripening (see Figure A). Luminaire designers are responding by building fixtures with the appropriate combination or ‘light recipe’ to maximise growth and development throughout the plant’s life.
Quality and reliability
Designing and building systems for use in greenhouses and indoor farms is a potentially lucrative business. However, it is not as straightforward as simply selecting red and blue LEDs to match the wavelengths in a grow light recipe and assembling them into a fixture. Designers should be mindful of the tough, high humidity, variable temperature environment of a greenhouse. Some growers have had bad experiences with poor quality or environmentally unsuitable components as well as poor design through inappropriate device matching.
Starting with the LEDs themselves, there are many manufacturers, but big name vendors, such as Cree, Lumileds and Osram Opto Semiconductor are the highest profile, delivering proven high efficiency and appropriate brightness, long life devices. Most of the industry-leading, successful grow light suppliers base their systems on devices from these companies.
With a strong focus on the horticultural lighting market, Osram offers the Oslon SSL range, featuring red and far red LEDs centred at 660nm and 730nm, as well as deep blue devices centred at 450nm. Other colours, including orange, yellow, green and white are also available. The company continues to monitor the latest research in this field and is actively involved in LED lighting metrics and standards development activities for the horticultural market.
From Lumileds, the LUXEON ranges are ideal for the grow light market, with the LUXEON C series of high power, low domed devices featuring one focal length for all colours to deliver flawless colour mixing. Other ranges include the LUXEON Z series high power, undomed LEDs for design flexibility, and the LUXEON Rebel series offering the highest efficacy. All are available in blue and red, with the LUXEON C and Rebel ranges also in deep red and far red. Lumileds is also a prime mover in the horticultural lighting arena and has been instrumental in developing and testing a wide range of grow light recipes.
In many electronics markets, the trend is towards sourcing more highly integrated components, sub-systems and assemblies. LED lighting is no exception. Ideal for designers less experienced in the technicalities required to assemble LEDs into arrays, a wide range of linear modules, clusters, floodlights and complete light engine kits are becoming more readily available. Intelligent LED Solutions (ILS) is one such supplier, with a strong line-up of products aimed at the horticultural market.
Built exclusively with Osram LEDs, the company offers strips, clusters and flood lamps with a combination of red, far red and blue arrays. Designed with thermal management in mind, the arrays are built on aluminium substrates. The datasheets recommend suitable heat sinks and power supplies. The company also supplies heatsinks, cables, lenses and mounting accessories.
At a higher level of integration is the ILS Petunia range of lighting kits, designed for greenhouse lighting. Solutions available offer a range of colour mixes (red, blue and white) for general purpose, seedlings or vegetative growth. White LEDs are added to provide lighting for the greenhouse or indoor farm workers when sunlight is absent. Complete kits contain the 12-diode array, a constant current LED driver, as well as heat sink, heat sink adaptor, lens and fixings.
Whether starting at the component or system level for the luminaire and its associated driver/power supply, a host of ancillary functions will also be needed in commercial installations, particularly for automatic operation and re-programmability (Figure 2).
Monitoring the environment within the greenhouse is critical, requiring ambient light, temperature and humidity sensors. Watering and cooling systems will require pumps, fans and shutters as well as their associated motor drivers and controllers. Data from the sensor and control systems is communicated to a central electronic MCU unit, which also has overall control of the lighting system. External communication, wired and/or wireless is important for status monitoring and for making program changes through the control electronics and software.
Connecting these various functions requires connectors, cables, housings and bus drivers, while power considerations, converting from AC to DC and back again, needs some consideration. Further, in the high humidity environment of a greenhouse, IP-rated components are preferable to ensure reliability and long life.
To source such a diverse and sometimes specialised range of devices, a broad-range component distributor with a comprehensive website is an obvious start point. In order to meet the various, and sometimes complex, system-level and project-wide constraints, it is important to select components that will work well with each other in the application. At RS, for example, when viewing online the Osram Oslon SSL series single colour LEDs, essential extras such as LEDiL lenses are displayed alongside. A search for LED drivers suitable for greenhouse lighting, normally constant current, turns up the Mean Well ELG ranges, covering a broad range of power and current outputs.
RS also makes recommendations that make a good match for greenhouse lighting applications. These include ambient light sensors from AMS, designed specifically for the rigorous process control industry; combined temperature and humidity sensors from Sensirion; and flow meters, also from Sensirion.
Opportunities abound for OEMs keen to supply the burgeoning greenhouse lighting market. Whether designing custom units from the component level upwards, or by incorporating more highly integrated arrays, modules and subsystems, the facility to source as many of these specialised devices and system components from a single supplier is a boon. RS offers a range of products and kits to support designers with their specific requirements.
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