The power and potential of light – the LED way
LED light technology is changing glasshouse operations in many ways.
All LED light given to crops can be converted into growth – that’s what international lighting experts told tomato growers at an open day in August.
Growers and horticultural industry representatives came from around the country to learn about new ways that LED lighting is changing glasshouse operations around the world. It’s rare that they gather together in such a mass scale apart from annual conferences and national meetings, but they did so to see first-hand new innovative lighting technology recently installed at Gourmet Mokai tomato glasshouse operation, just north of Taupo. This is the first installation of LED toplighting and LED interlighting in a New Zealand commercial horticultural setting.
The day provided an opportunity for growers to listen, learn, ask some hard questions, look at a LED greenhouse operation – and it also got them thinking about how such new technology could benefit their operations.
It was organised by international industry giant, Dutch-based lighting and electrical manufacturer, Signify (formerly known as Philips Lighting). The group’s plant specialist for highwire crops and soft fruits, Piet Hein van Baar, took the growers through a short history of LED trials to date and provided an overview of the practical and technical aspects of installing and running LEDs in a commercial glasshouse setting.
With insights from his team’s hardearned experience and humour, Piet, captivated the audience. This included a one-liner that made laughter ripple through the audience, “This is no fake news.”
Signify’s Australian-based key account manager for Philips horticultural lighting, Aart Slobbe, discussed his work in developing individuallytailored systems helping growers achieve better results. The audience heard from NZ Gourmet’s production
director, Protected Crops, Roelf Schreuder, and Mokai onsite senior grower, Hans van Veen, who outlined their experience of integrating and using the new technology in the operation.
Piet said that since starting with LEDs 11 years ago, the company has been at the forefront of trials, grower partnerships and new start-ups in Europe and in new city farms in the United States. Mainly Piet’s work has been with growers of high wire crops like tomatoes, peppers, and young plants.
He said it’s one thing to make and sell light, but Signify should also be able to give advice about what to do with that light because growing with LEDs is so different from using conventional sources, such as high-pressure sodium (HPS) or solely with natural sun lit operations.
It was in 2012 that the first commercial greenhouse in the Netherlands started with interlighting, and in 2014 the team opened the first commercial city farm in the US and had its first international high-wire information sharing event.
What became apparent early on in the discussion is the team had taken number-crunching and analytics to a high-level – there is virtually no guesswork involved. But the waiver is the predictions are only as good as the raw data that individual growers have on hand to start with.
With the first Northern European operations, the challenge was to improve winter production while maintaining consistent high quality. One of Signify’s best stories so far involves a grower in Finland. This northern grower has a 3000m² glasshouse operation, where he proves tomatoes can be grown in winter conditions of -23 °C with full LED, said Piet.
In another project, the company is working with a grower in Russia who started with 25ha under full LED, and has recently decided to extend its operation with 37ha this year due to high production figures and improvements in crop quality.
Controlling your own climate
Since starting with LEDs 11 years ago, the company has been at the forefront of trials, grower partnerships and new start-ups in Europe and in new city farms in the United States.
LED lighting’s trump card is mainly about energy efficiency – and without the danger of too much radiant heat and energy wastage. The ability to have more control over climate is also an important factor.
The placement of the LED has much to do with overall canopy success. Traditional high-wire glasshouse growers use top light which fades away as it penetrates the lower structures.
High-wire crops face an added challenge because their abundant crop canopy limits overhead light from reaching the part of the crop that needs the light most. In fact, overhead lighting provided by top lighting modules usually penetrate to only about 75cm below the crop canopy.
Trials proved that placing LEDs in the middle of the crop was the answer. For example, placing LEDs in a horizontal strip in between the third and fourth truss of a tomato crop, adds light to areas which usually suffer from light starvation. This is called interlighting.>
Placing LED lighting within the canopy directs and focuses growth stimulating light on the most vital part of the crop. By applying a sideways light distribution pattern, the leaves can more efficiently transform the light into growing more yield.
LEDs have significantly more light power compared to HPS per electrical watt, and far less radiation heat compared with HPS and sunlight. LED light can be far more exacting using the colour spectrum that affects photosynthesis.
A light recipe
All plants have different light needs. Philips GreenPower LED lighting offers growers a choice of ‘light recipes’ which are dedicated combinations of spectrum, intensity, timing, uniformity and positioning within the glasshouse environment. The company has developed these tools over many years of co-operation with city farmers, greenhouse growers, universities, and research organisations.
The Philips LED modules come in multiple spectral versions, which have combinations of two to four light colours. Different light colours can have different effects on crops. But commonly deep red is the most efficient for photosynthesis, vegetative reproduction and stimulation of shoot development. Far red has a positive effect on generative properties, flower formation and rooting. Blue has positive effects on compactness and hardening. White is a working light with the full spectrum of colours.
LED provides a platform in which growers can play with the light spectrum and pick the spectrum that’s best for their crop. Individual light recipes make it possible to steer specific plant characteristics and to suit
different plant varieties such as compactness, colour intensity and branch development, resulting in optimised crop yield and quality.
Selecting from the spectrum
In white light, plants are seen as green because the leaves don’t absorb green light, but partly reflect it.
Piet challenged the audience’s thinking.
“The spectrum of sunlight has everything; UV, red, green, blue – all together it makes white,” he said.
“But do plants use everything in the same way? Is all that spectrum of light needed to grow your plant?
“HPS has many ranges of blue, green, and yellow but not that much red light. But if you look at plants, in particular tomato plants, they need blue light to open the stomata and get the right morphology into the plant, and red light is mainly for photosynthesis. Red light is the most important thing for growing. That’s one of the reasons we put so much red light into these modules.
“If you see the greenhouse at night with the red and blue lights, the plants appear totally black but they would still be growing.”
Adding interlighting into the canopy creates more photosynthesis – particularly around the bottom of the crop, said Piet.
With LED – all the light that you give to the crop can be converted into growth, offering growers the potential to have higher plant densities and fruit weights, Piet said.
Working out individual recipes starts with forming a numbersbased growth plan. Signify uses the measurement of ‘micromol’ for calculation.Rather than a blunt instrument of using total production, the better and fairer way to judge how good a grower is doing, is by using the calculation of grams per mol of light.
“We start with a reference with daylight only because we want to know how good you are as a grower,” he said.
“From here we can calculate how many grams per mol of light a grower produces. We always calculate everything back to grams per mol, this is also a way we are able to compare different growers. If you only look at the production kilogram per square metre it’s not fair because growers have different light levels in micromoles/m²/s.” Grower questions
At question time, one of the growers asked about the nutritional value or taste differences using LED.
All plants have different light needs. Philips GreenPower LED lighting offers growers a choice of ‘light recipes' which are dedicated combinations of spectrum, intensity, timing, uniformity and positioning within the glasshouse environment.
Piet answered by saying, “we cannot say if you add LED that you’ll get better taste. Taste is created by the variety and the
grower, and how growers treat their crops, however, we’ve seen with LED the green part of the trusses are getting stronger”.
Another grower said that in New Zealand, there aren’t many growers with HPS systems, and most Kiwi operations have no supplementary lighting - so that starting point would be daylightonly models. So would the implications of interlighting and toplighting with LEDs be more significant?
“What you have to keep in mind in New Zealand is that you do have high light levels, even early in the winter time,” Piet said.
“But when your light starts decreasing also the radiation heat from the sun starts decreasing.”
Roelf said with New Zealand’s climate, when the sun comes out, it’s powerful and heats the greenhouse straight away.
“You want to have heat in the bottom of your crop to get quick ripening of fruit, while keeping your head as cool as possible. When we thought about putting in HPS it would mean too much heat at the top of the crop. Going through that exercise and seeing the effect of the heat, we backed off HPS and started talking to Signify again about their Philips LEDs.
“With the light at the top of the crop, it makes you look at the crop in a different way – LED works well and it was a good decision for us not to have HPS in here.”
Power consumption is another important factor. HPS uses a lot more power, and that gap between the two levels in power use, means the Mokai operation will earn the purchase price difference back in five years’ time on the power savings, Roelf said.
The LED equipment is projected to last at least 35,000 hours, resulting in lower maintenance and running costs. Signify specifies 35,000 hours, and even at 35,000 hours they still have 90 percent of the original output that was originally installed. Research shows modules in operation for seven years are still at 98 percent total efficiency, Piet said. Another question was asked about the CO2 enrichment - at what point is extra lighting being negated by lack of CO2?
“You want to have heat in the bottom of your crop to get quick ripening of fruit, while keeping your head as cool as possible.”
Piet said the answer was simple; the moment the plant gets light, it needs CO2 but when lighting is halted during the night, then photosynthesis levels are extremely low.
“I have two rules when LED is switched on. You have to put CO2 into your crop and heat your greenhouse. Lighting during the night with LED without high temperature can be likened to a museum – the plants will look excellent but they don’t grow.”
Another point was made about oversaturating plants from the top with light. Saturation point for toplighting has been found to be around 425450 micromols/m²/s of light. After 450 micromols/m²/s, adding more light is virtually no use. Plants respond best between 250-450 micromols/m²/s.
“With LED interlighting we bring PAR light into the canopy of the crop and there we have our ‘X’ factor,” Piet said.