Why LEDs have a key role in the horticulture revolution

Alexander Wilm of Osram Opto Semiconductors explains how LEDs – and scientific advances – are completely changing the way we grow plants.

In the most basic sense, light is crucial for most living things residing above deep sea level. Plants use light to develop by a process of photosynthesis, where CO2 is converted into carbohydrate in the chloroplasts of the plant cells. It is also possible to enable photosynthesis using artificial light, and control the development, shape, and flowering period of a plant. The quantity of light, its quality - in regard to spectral composition of light - and light duration all have an effect on plant properties when growing and matured. Therefore, lighting (and its technological developments) is a crucial variable in today’s horticultural industry.

As an example, the fresh fruit and vegetables market in Europe (worth over €30 billion according to ICI Business) is currently being hit with a number of external factors, including the changing climate, heightened consumer awareness of the health benefits, the increase in demand for niche ‘superfoods’, supply chain costs, and pressure to ensure sustainable and ‘greener’ and also ‘local’ horticultural practices. 

With these kinds of challenges in a growing market, the industry has made several advances to increase production to meet demand, and ensure that lead times to reach the final consumer are effectively met. Indoor cultivation in a greenhouse or an enclosed building with artificial and controllable lighting have become a popular way to make the best use of conurbations with limited space. This kind of lighting also enables farmers to supplement natural daylight for faster, higher quality plant growth, to extend the daylight period or simply grow completely without natural daylight in an enclosed space. Among other things, farmers can also grow fruit, vegetables, flowers, and other flora that their home climate conditions may otherwise deny them - for example, growing exotic fruit in an disused warehouse in a city.

Multi-layer or ‘vertical’ cultivation, which sees flat rows of plants positioned above each other has also enabled space-saving but new farming possibilities have usurped these systematic approaches. Going one step further, ‘3D farming’ is another advancement that sees cleanroom-like environments, ‘Fardominiums’ and transport combined with cultivation containers. Controlled environment farming has been proven to be a better alternative to traditional farming to ensure sustainable food production for an ever-growing population. Benefits include no agricultural runoff from a closed system, no unnecessary use of pesticides, herbicides and other chemicals (as crops are protected from pests and contamination), and a contribution towards ecosystem repair.

However, optimising the best possible conditions for plants – and keeping that consistent for all of the plants, no matter where they’re positioned – completely depends on what is important to a grower. Both the two main factors of required yield, quality and control (e.g. yield per harvest, fruit size and weight, colour and flavour) and speed, cost and material efficiency (e.g. time to germinate, cycles per season, minimising water and energy per harvested plant, speed of growth) dictate the best possible lighting for each situation.

Yet, lighting systems are a key challenge with these advancements, especially in tightly packed growing environments such as those seen with vertical or 3D farming. Incumbent horticulture lighting is usually based upon High-Pressure Sodium (HPS) lamps. HPS lamps produce over 100 lm/W, but over a wide wavelength range. The high power consumption and the heat of HPS luminaires also demand a significant distance between the light source and the plants, leaving them primarily suitable for toplighting systems in growing facilities. Other drawbacks of HPS lamps include a short lifespan of only 8,000 hours, and smaller lamps are significantly cost inefficient.

Since the discovery was made that the spectrum of light offered to plants can change plant properties (for example, blossom and fruit growth rates), there has been an enormous increase in the interest shown by the horticultural industry in LEDs. This is where LED lighting has become a crucial technology for the viability of sustainable urban farming.

Light offered to plants can change plant properties (for example, blossom and fruit growth rates)

Green plants predominantly use blue light (around 430 to 490 nm) and red light (around 640 to 780 nm) for photosynthesis and producing energy, but also have other absorption bands such as around 730 nm in infrared range. This range controls plant growth, among other things. The right mix and the temporary addition of certain wavelengths – adapted specifically to the individual needs of the plant – can then trigger the desired effect in line with the yield, quality, control, speed, cost and material efficiency goals of the grower. LEDs are particularly well suited to this application, down to a defined colour spectrum and flexible control.

For optimum plant growth, the light must offer these aforementioned wavelength ranges, and avoid having an overall white appearance, as we may be used to seeing from LEDs. 

Incorporating an LED system that cover the optimum wavelength range means that lighting can be adapted to suit any type of plant or flower. Varying the number of LEDs providing a light source to achieve different ratios is possible without needing to amend the printed circuit board or the design of the luminaires. 

The OSLON SSL portfolio from Osram Opto Semiconductors is a 1W class LED that offers a prefocused 80, a standard 120 or a wide 150 radiation pattern, avoiding the need to purchase additional lenses. A highly targeted spectra ensures that chlorophyll absorption and photosynethesis in plants is increased. It also covers wavelengths from 450nm to 660nm for deep blue to hyper red, and 730nm for far red light (critical for the flowering of many plants).

Once the right LED system is successfully implemented, plants can be cultivated in enclosed spaces under artificial light and away from the elements. The flexibility of control also means that all-round lighting can be achieved, therefore the plants aren’t expending energy looking for the sun; instead they focus on growing outwards, and faster to produce higher yields. 

Design wise, any luminaires and the LEDs contained within should be able to withstand the environment of the greenhouse or building (for example, humidity caused by sprinkler systems, or dirt and chemicals from any fertilisers or insecticides that might be used). 

Lighting consistency of illumination and uniformity in terms of how much light each individual plant gets (to ensure even growth and encourage yields to be synced) is also important, particularly in vertical farming or 3D arrangements. Because of their small footprint of 3.0 x 3.0 mm2, OSLON SSL LEDs lend themselves to closely packed arrangements to ensure a uniform light impression on the plants, and the low temperatures of LEDs enable the use of interlighting in between plants and leaves to increase the quantity of light, and minimise the risk of the ‘shadowing’ often caused by toplighting.

Today, LED lighting can stimulate plant growth by up to 40 per cent. Durable and long lasting LEDs are also a much more environmentally friendly alternative to standard horticultural lighting. They can significantly stimulate plant growth while drastically reducing energy consumption through the use of targeted lighting at 450, 660 and 730 nanometres. LEDs provide a strong option for lighting for all types of plants and flowers, enabling the grower to adapt the light exactly to the needs of various crops.

The features of LEDs for horticultural lighting such as small form factor, high efficiency and long life, all provide flexibility for growers. Dimmable and controllable, LEDs are ‘instant on’ when you need them and can easily be set in cycles that promote healthy plant growth.

  • Lux's sister title LEDs Magazine is hosting a special conference dedicated to the emerging market of horticulture lighting. It takes place at The Palmer House Hotel in Chicago on 12 October 2016.  For information, click HERE

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