A light salad: LEDs revolutionise the horticulture industry

With their low energy usage, reduced heat output and the ability to control the light colour they emit, LEDs are poised to revolutionise the horticulture industry.

Farms like Colangelo`s offer a tantalising vision for the future of farming. They allow for faster, more efficient growing, significantly less waste and the ability to produce crops near or even within cities – where most plants are now consumed. This potential revolution is, above all, powered by LEDs.

Plants need light to provide the energy that lets them create their own food: they capture this through chlorophyll, a pigment in their leaves. Until relatively recently, there have only been two commercially viable ways to provide plants with this light: using the Sun, or via high-pressure sodium lamps (HPS) installed in greenhouses.

The Sun is, of course, undependable – cloud cover can limit the light available to plants, meaning crops grow more slowly. Growing outdoors also introduces many risks – from too much or too little water, pests, and the requirement to use pesticides. You can also only grow on one level, meaning farms require a huge footprint.

HPS lamps have advantages over the Sun. When installed in a greenhouse they can provide a constant source of light – even when the Sun is behind clouds or when days are shorter. However, Simon Thaler, press officer at Osram, the German lighting manufacturer, explains their drawbacks: [HPS lamps produce over 100lm/W [lumens per watt] but over a wide wavelength range, which is not necessarily optimised to plant growth. The high power consumption and the heat radiated from HPS luminaires also require a significant distance between the light source and the plants, leaving them primarily suitable for top-lighting systems in greenhouses. To compensate for the heat development, they also often require additional hydration of the plants."

LEDs offer many advantages over these traditional light sources. They do not warm up the surrounding air in the same way as HPS luminaires do, meaning they can be placed much closer to plants in stacks – allowing for `vertical farms` like Colangelo`s. Thaler notes that LEDs last significantly longer than HPS lamps and use less electricity. They can also be turned on and off in seconds – which is more effective than HPS lamps that require up to 30 minutes to reach capacity.

However, perhaps the most exciting thing about LED is that it gives growers control over the kind of light that the plant is exposed to. As it turns out, plant growth is especially benefited by light in the blue or red part of the spectrum. LEDs can be designed to specifically generate more of this kind of light, which is especially useful for growing plants.

Professor Neil Mattson, a horticulture researcher at Cornell University in New York, describes his lab`s research into LEDs and light. [We look at plant performance when the plant is exposed to different spectra of light, and how this affects the plant`s qualities. For instance, if you expose the plant to more blue light, this produces a plant with thicker leaves. It can also turn on the pathways for secondary benefits such as a plant which contains more antioxidants."

Mattson describes cutting-edge research which looks at how different light wavelengths mean you can get taller or shorter plants, earlier flowering, or impact nutritional value. His current research has found that [lighting treatments can double the amount of vitamin C found in a tomato", for instance.

Brandon Newkirk, marketing director at smart lighting company LumiGrow, explains how his company`s LEDs provide growers with this kind of cutting-edge control today. The Californian company has developed cloud-based software that connects to its lighting hardware. This allows growers to constantly monitor light levels in their greenhouses and then `tell` the LEDs what to do according to their own automated growing strategy –whether that`s exposing the plant to more LED light or reducing it on sunny days to bring down electricity costs.

He describes custom-designed treatments, or `recipes`, that expose plants to either more red or blue light. These kinds of treatments can, for example, [make for a sweeter or spicier basil leaf". LumiGrow`s customers can effectively design the ideal produce that end consumers might want by exposing the plant to different light spectrums at different stages of its growth. Newkirk explains how, for example, lettuce plants could be exposed to more blue light towards the end of their growth cycle in order to give a more vibrant colour to the final product.

For the end grower, LEDs have the added benefit of giving them much more predictability – and this can save them money. Professor Marc van Iersel from the University of Georgia reports that in the US alone, around $600m is spent every year on energy used in horticultural lighting. If growers can cut that cost by using more energy-efficient LEDs, then they can boost their profit margins. What`s more, he explains that [in the US, by the time a grower plants a crop in a greenhouse, it`s already been sold". LED lighting means growers can confidently provide the plant with the right amount of light to ensure it will grow in time – because when growers miss deadlines they are often hit by financial penalties.

LEDs clearly have enormous potential. However, Mattson notes that only around 2 per cent of US greenhouses currently use LED technology, according to a recent Department of Energy study. What`s stopping uptake?

Put simply, LEDs are more expensive to buy than HPS lamps or sunlight. Prices will go down – van Iersel expects the technology to keep improving while costs drop over the coming decade. And companies like Osram and LumiGrow point to the longer lifespan of their products and reduced electricity bills.

Then there`s the question of return on investment (ROI). Mattson explains that for certain crops, it may take up to 10 years to achieve payback, although lighting firms assure ROI is normally achieved in less than five. Either way, growers expect ROI fast, meaning that many still have doubts about whether the investment is right for them.

And there`s the final price for the plants themselves. LED lights can, in theory, be used to grow any plant. However, at present the economics doesn`t make sense for anything but the highest value crops such as salads, herbs, flowers and marijuana. From apples to potatoes to wheat, many cheaper crops are already pretty much perfectly farmed in the great outdoors, meaning LEDs would offer limited value. Van Iersel describes a colleague`s calculation, which estimated that, should wheat be grown under LEDs in the US, a simple loaf of bread would cost an extortionate $11.

He explains that [it`s frustrating for people like us working in the field, because there are various `visionaries` who claim that in future all produce will be grown in warehouses. But, as the example with the loaf of bread shows, that`s not going to happen any time soon."

Besides the cost aspect of LEDs, Colangelo of Green Sense Farms also highlights other practical industry challenges, especially for vertical farms. There`s a general lack of workers in the agricultural industry, and even fewer who know how to build and rig up LED farms. [There`s no standard textbook on building a vertical farm yet."

Despite these challenges, rapid advances in LED technology suggest we will reach a tipping point soon – Mattson estimates this will be reached within 5-10 years. At this point, LEDs will be more attractive and cost-effective than HPS, and this could really revolutionise the horticultural industry.

Colangelo expects to see farming become more stratified, with different types of crop being grown in the most appropriate environment. Some plants will always be best grown under the Sun, some in greenhouses and others in vertical farms.

He adds: [People get very excited to see plants growing indoors in a very sanitary environment."

If he`s right, the future`s bright for the sector.