The sight of around a dozen companies exhibiting LED-based technologies at October's Horti Fair in Amsterdam suggested that the technology is on the brink of a breakthrough in horticulture.
Notable among these was Dutch electronics giant Philips. The company, which already manufactures a range of LED-based amenity lighting, has spent the past two years on field work to develop LED products for horticulture. "We have been below the radar," says global product marketing director for horticultural lighting Udo van Slooten. "We've been going to a grower, seeing how he normally grows his crop and what LEDs can do for him," he says. "We've been doing tests with all kinds of crops, but have targeted layer applications and research. Light demands are not so high in propagation, tissue culture and young plants. And there are a lot of companies in those sectors."
With multi-layer growing, the problem is heat, and light distribution rather than the amount of light, Van Slooten says. "On a shelf arrangement, the middle gets more light than the edges (with conventional lighting)."
As well as finding the optimum light levels, research involves looking at the effect of the light's composition. "Different wavelengths have different functions in a plant," he says. "Deep red at around 660nm promotes growth, whereas far-red (bordering on infra-red) light has a steering function - for example, promoting flowering."
He gives as an example the growing of lollo rosso lettuce under LEDs. "Our first trial tasted fine, but the leaves didn't turn red - for that we had to add far-red light," he says. "It shows the importance of the spectrum."
"The alternative approach is to go straight to the greenhouses and replace conventional assimilation lights one-to-one with LEDs but you need a lot of light for that and LEDs are too expensive." Instead, Philips is looking at combining HID (high intensity discharge) lighting from above tomato crops with LEDs between crop rows. "What we ask is, where is the added value - the X factor - that LEDs can bring for a particular crop? It may be better quality or higher production."
Van Slooten admits that X factor may be more difficult for roses, which rely on top lighting, than for edible crops. "We will set up tests for those too, but it will take longer to make it commercial," he says.
An ambient temperature will affect the life expectancy and light output of LEDs but Philips' are specified to last 25,000 hours at 90 per cent intensity or above, Van Slooten adds. "The lifetime of an LED depends on it being kept at an optimal temperature - otherwise the light output goes down. So far the focus has been in the Netherlands, but now we are looking elsewhere, both for partner growers and intermediary companies."
One partner company is specialist grower Peerdeman Orchids of Andijk. According to owner Arjen Peerdeman: "We were surprised to discover that LEDs really do make a difference. The flexibility to optimise the different factors - spectrum, uniformity and heat distribution - ensures the ideal solution."
Meanwhile, breeder and propagator Royal van Zanten has already found an application for LEDs in tissue culture and plant storage. "As well as saving energy, LEDs help us to improve plant quality during cold storage, mainly thanks to better heat control," says research director Sjoukje Heimovaara.
Taking a different route is Lemnis Lighting, a company co-founded by Warner Philips, great-grandfather of the founder of Philips BV, and one of 34 firms to be honoured as a "Technology Pioneer" at the World Economic Forum in Davos, Switzerland, later this month. It claims that its roof-mounted LED assimilation lighting delivers the same plant growth as conventional lighting while using only a quarter of the energy.
Wageningen University researcher Frank Kempkes says: "The problem with LEDs is that output is so much lower than input. But by giving the plant light of a particular make-up, say 80 per cent red to 20 per cent blue, you can work more efficiently."
Clearly it is an area where both manufacturers and growers are still learning. BPOA technical committee chairman Michael Smith says: "It's moving forward at pace, but there hasn't been enough research.
"So far we are relying on the manufacturers - no one has trialled LED lighting independently. The BPOA is gathering information on it at the moment, just seeing what's out there, with a view to getting together our own research proposal."
Smith, who is a director of bedding grower WD Smith & Son, adds: "It could work for us - there are some interesting ideas on controlling the light spectrum to regulate growth. People have tried doing that with films, but that hasn't been taken up commercially. There's potential, though."
East Yorkshire-based horticultural equipment manufacturer HotBox already has RosaLux and BlauLux LED assimilation lights on the market. According to sales co-ordinator Sabine Holliday: "Growers asked Roland Spencer, who designed HotBox's products, to design an LED for them, so he did. It's still experimental, but everyone we've given one to has great results. One tomato grower in Hungary has seen a 25 per cent increase in crops."
LEDS: PROS AND CONS
- Energy consumption is much lower than sodium of fluorescent lamps, since output is concentrated at specific wavelengths
- Less heat radiation, so not only more efficient but allows more compact unit design without risk of overheating
- Safer, thanks to low heat and voltage
- Longer life than conventional bulbs
- Expensive - currently around 10 times more costly than conventional assimilation lighting
- Lack of understanding - tailoring light wavelengths to optimise plant growth is still a young science
GreenPower LED module and LED string are designed for multi-layer applications requiring only low light levels, such as tissue culture, storage and transport, where they offer uniform light across shelves.
Light intensity and composition can be controlled with a high level of accuracy. They are also waterproof for ease of cleaning. The LED string offers additional flexibility to designers, leaving the door open to innovative configurations.
The products have already found a market in the plant research world. According to Dr Wim van Ieperen of Wageningen University & Research Centre: "The GreenPower LED module is clear and reliable in its specifications and gives us a great deal of freedom when working with it."
HortiHotel (Grow Technology and partners)
One example of an application for the Philips LED module is the HortiHotel closed growing system from Grow. Taking the form of enclosed lightweight multi-layered trolleys, the system offers growers and researchers complete control over all growth factors, says researcher Tanja Huijben. "No daylight gets in, so you can shorten the plant's circadian rhythm, giving you an extra day a week," she says.
Software controls temperature, relative humidity and air composition as well as lighting. By creating an environment low in oxygen relative to CO2, photosynthesis is increased relative to respiration. And a closed atmospheric system protects from pest and disease outbreaks, requiring fewer chemicals. "They are really expensive and your customers don't want you using them," says Huijben. Meanwhile, evaporated water is condensed and recycled with 95 per cent efficiency. The system is already in use at a Dutch Anthurium young-plant grower.
It also has research applications as it allows one variable to be changed independently, even to extremes. "All different climatic conditions can be imitated, so that the ideal plant can be developed, anywhere in the world," she says.
Jaz (Ocean Optics)
The Jaz is a multi-purpose handheld spectrometer able to measure the output from LED lighting. When fitted to climate computer, it feeds back this information to ensure optimal LED output, says Ocean Optics commercial director Marco Snikkers.
"LEDs are really starting now," he says. "Growers are testing them and they are getting better and stronger."
The US-made device can also measure several optical characteristics of the plant itself, including reflectiveness, giving a warning of any stress. "It tells you about the plant's health and whether it needs fertiliser."
Vice-president of sales and marketing Mike Kayat adds: "As energy savings and cost concerns help drive demand for more efficient LEDs and other types of lighting, the value of simple, convenient diagnostic instrumentation is magnified." An optional holster ensures full portability.