We all know that light is one of the essentials for plant growth and that the cheapest source comes free from the sun. But it is not always available or not in the quantities, intensities and qualities that our plants, and our businesses, need. To increase production and plant quality it has become common practice to use artificial light. Unfortunately, that has been costly.
Traditional plant lighting, such as SON-T lamps, can be expensive to buy and to operate. Their energy consumption is high. They are also unable to turn on and off quickly and efficiently in response to changing ambient conditions. Rapid light loss generally occurs after 12,000 hours runtime and the light might not be evenly distributed due to the nature of the bulb and fitting.
They produce excessive heat - a waste, but this also makes it difficult to achieve optimum growing conditions in terms of temperature and in many cases requiring cooling as an input. Another important factor is that the spectral output of traditional plant lamps may not match the requirement of the crop.
Plants use light at 400-700nm in the radiation spectrum. This is called photosynthetically active radiation, or PAR-light. For efficiency, a plant growth lamp must convert as much electrical energy as possible into PAR energy. Older lamps hit that range but produce energy concentrated in just a small band, typically 560-630nm. It is not optimal light.
Such problems associated with traditional plant lamps, combined with the ever-rising cost of electricity, mean that many commercial growers have often had to find a compromise solution and have been unable to extend the growing season into the winter months.
The arrival of commercially viable LEDs is changing all that. For starters, they are more energy-efficient and last longer. They switch on and off quickly and produce little radiated heat so they can be positioned closer to the crop. More even light distribution can be achieved. Then there is the spectral output. This can be matched to particular applications and only the parts of the spectrum required by the plant can be produced. "Recipes" can be created according to plant type and growth stage.
Demand for LEDs in homes, offices, shops and industry has brought about rapid development in the technology over the last 15 or so years. It also meant manufacturers focused much of their R&D budgets on those markets. By comparison, research into the use of LEDs for horticultural applications was small, although horticulture can benefit from the advancements made generally in LED technology and its usage elsewhere has helped to lower the capital cost of equipment.
Companies are now increasing effort in plant growth lighting and a speedy expansion is expected as greenhouse growers, vertical farms and plant factories take up the advantages of the latest-generation growth lights. RnRMarketResearch.com's 2015-21 report released in March this year stated that rapid adoption of LEDs in general and rapid adoption of LED growth lights worldwide is occurring as systems provide peak growing efficiency.
The report continued: "LED grow lights are shifting as illustrated by the new Everlight GL-Flora LED lighting fixtures for agriculture.
They offer low power, high-efficiency, uniform light pattern, homogenous light distribution at precisely the right wavelengths and colour ratios needed for superior photosynthetic response."
Philips, Valoya, LumiGrow, GE and Everlight Electronics are among the manufacturers that are currently involved in the development of plant growth lights. Here in the UK, Surrey-based PhytoLux believes the future is looking bright for LED plant growth lighting.
"LED plant growth lights for use in horticultural research and commercial food production have been gaining traction in the industry for some time," says PhytoLux managing director Steve Edwards. "Following extensive research and development over the past five years, the clear benefits from using these lights have become recognised across the sector and have gained real momentum in the past 12 months."
PhytoLux has taken an engineering approach in the design and development of its Attis range of LED plant growth lights to offer a commercially viable, high light output solution. It has units in use with more than 40 organisations in the UK, ranging from universities to major research establishments and commercial growers - including seed producers, propagators and commercial soft-fruit, tomato, herb and bedding plant producers.
Some impressive results have been recorded over the past 12 months. Earlier in the year, PhytoLux held a seminar at the Rothamsted Research facility in Harpenden to share knowledge with those trialling the Attis range of lights.
The key objective of the trials for Rothamsted Research has been to find a solution that will produce similar or improved growth results when compared with the high-pressure sodium SON-T lamps previously used in its greenhouses. The head of the horticultural and controlled environment department at Rothamsted reported that energy savings in excess of 70 per cent had been achieved.
At the University of Bristol, stockier, more compact plants with better developed leaves and an average energy saving of 71.4 per cent was achieved. At Cardiff University plants were also reported to be stockier and stronger, with faster and denser inflorescence, better developed rooting systems and shorter inter-nodal spacing.
More trails were conducted at Moulton College and the University of Greenwich. PhytoLux accounts manager Laura McLean describes the trends: "At Moulton, more compact plant morphology resulted, with higher chlorophyll content, thicker and sturdier leaves, faster growth rate and higher dry weight, whilst root-shoot ratio was maintained."
She continues: "At Greenwich, plants propagated by tissue culture under the PhytoLux lights rooted faster with a greater number of roots and sturdier root systems."
Increase in crop yield and extension of season are the key factors sought by commercial growers, along with the need to maintain high quality of produce. Edwards says: "Whether it is an energy save of up to 65 per cent over traditional SON-T lights, or about achieving an extension to the growing season with higher yield volume, then we have a solution that fits the requirements of most organisations. We have seen a tomato crop yield match that of our client's Spanish operation through the winter, which is a significant achievement, and have seen ripened strawberries delivered to the customer on Christmas Day."
Within the edibles sector, the use of the broad-spectrum PhytoLux LED units has also enabled an improvement in flavours. "This is the beauty of LED," adds Edwards. "We have developed a generic LED solution to provide a successful growth light for a wide variety of plant and crop species."
Trials that began in December 2013 in the fully enclosed controlled-environment chambers at the University of Oxford have resulted in the development of a new range of lights specifically for applications using tiered racking and with no ambient light. Following on from this, a unit has been developed with supporting control system to enable control of nine light wavelengths with adjustment of the light spectrum to suit the plant.
Vertical farming solution
A project has now been launched with a major UK grower and controlled environment engineering company to develop a fully functioning, fully enclosed vertical farming solution that has relevance to both the research industry and the food-production industry.
The farm, which is due to be constructed in the autumn, will use the light system developed at the University of Oxford. It will enable herbs and salad crops to be grown in a fully enclosed tiered system and will be programmable to provide optimum growing conditions for specific plant types, so allowing maximum food production.
"With the support of one of the UK's major retailers, we hope to develop a working solution in 2015 that will significantly help advance scientific research but also have a discernible impact on reducing food miles for the industry," says Edwards.
Whether it is for photoperiodic, supplementary or total replacement, LED technology is striving to provide solutions. With some significant installations now demonstrating proof of the advantages of using LEDs for plant growth purposes, it is believed the way is clear for a major expansion in the industry.
Calculators to help decision-making
The Farm Energy Centre has produced three calculators to help growers make decisions about the use of LED lighting. As a part of HDC-funded project PO10: LED Lighting for Horticultural Applications - Establishing the Economics of Current Hardware Offerings, the calculators relate to:
- Interlighting This calculator shows the costs and benefits of using LED interlighting for vine crops alongside traditional overhead lighting from high-pressure sodium lights or metal-halide lamps.
- Tiered growing This shows the costs and benefits of using LEDs in multilayer applications and for single-layer supplementary lighting.
- Photoperiodic extension This calculator compares using LEDs against traditional GLS or CFL bulbs for daylight extension.