Danish pot rose grower Rosa Danica invested in an LED lighting system earlier this year, improving plant quality and uniformity.
According to Paul van der Valk, international sales manager for Netherlands-based supplier Hortilux Schréder: “The grower wanted to save energy but achieve the same light intensity as they were currently using.
“We worked with them on the design where for most of the time, the LEDs provide all the additional light at an optimum spectrum for each stage of the crop, with the HPS used only when needed for the darkest days in the winter.”
Energy costs may have seen some growers in regions such as southern Europe switch supplementary lights off for a while, but at the same time, they have driven investment in energy-efficient LEDs in areas with lower natural light intensities. “Just four years ago, our sales were split evenly between HPS and LED: now it’s 90 per cent LED,” he says.
He adds, “And while it has up to now been common for growers to start with a hybrid installation, more are now opting to go straight for LED only.”
The acceleration in take-up of the technology, however, is seeing dozens of suppliers offering lighting to growers, which can make it confusing to pin down what best will suit your situation and crop. “With HPS, you had a choice between a couple of power outputs and a couple of different reflectors, and that was about it,” says Mr. van der Valk.
“With LED this year, we alone offer seven different power outputs, seven standard spectra and three different lens optics to control light distribution ¬– that adds up to 147 options just from one company. It’s now much harder for growers to compare offers.”
While plenty of independent advice is available to help you, he believes only five lighting companies worldwide have enough of a track record in horticultural LED installations. “It’s one thing making lights for a home, office or warehouse and another for a greenhouse,” he says. “The greenhouse environment is very challenging with its high humidities, fluctuating temperatures and need for a high degree of controllability, let alone efficiency and reliability.”
The starting point for designing an installation has to be an understanding of what the crop needs, he says. “A crop under LEDs has to be grown in a totally different way, not just because of the difference in the light itself and the ability to tailor the spectrum, but because the lamps generate less heat.
“That can be welcome for crops such as cut tulips, where the heat produced by HPS lamps often needs to be removed, but it also has an impact in areas such as humidity control. You’re not just swapping the source of light; the whole greenhouse climate has changed.
“That’s why we, for example, are part of the Plant Empowerment Foundation [a Dutch association of various specialist horticultural supply companies and universities], so we can work with experts in other aspects of environmental management such as screening and humidity control.”
The big gains in LED energy efficiency achieved in the last decade or so, which have made this form of lighting so attractive as an investment, are unlikely to be repeated in the next few years, says Mr van der Valk. “In 2018, a light output of 2.8 micromoles per joule of energy was considered really good. Now we see 3.5, and the price [of a fixture] per micromole has dropped. In the next two to three years, efficiency might reach 4 micromoles per joule, depending on the spectrum. But higher efficiency is also more expensive because, for example, these lights will need better cooling.”
More recent advances are all about controllability. He says: “The industry has already learned a lot about the light quality needed by different crops at different times of day, seasons, and growth stages. A key technical development now is controlling LED fixtures through dimming. With the latest digital dimming technology, you can precisely adjust light intensity depending on crop requirement; for example, young plants need a lower light intensity than a more mature crop.”
With modern LED fixtures producing light from four different colour LED ‘chips’ – red, blue, green (or white) and far-red – the current emphasis is on being able to dim each one separately to adjust both light output and the colour balance. “It needs more development as it’s currently expensive, but the goal is to be able to steer a crop by light quality.”
Switching several lamps off is the only way to control light intensity from an HPS installation. That will affect light distribution, which in turn can affect crop uniformity. “With dimmable LEDs, you dim each fixture equally, so you maintain uniform light distribution,” he says. Dimming also means the fixture runs cooler, increasing its efficiency.
The next step is wireless control. “This involves creating a network that can be used for other crop data. So, for example, a fixture would ‘know’ when the bench underneath it is empty of the crop and would automatically be turned off. The network can also be easily integrated with the climate control and even be linked to pest and disease monitoring systems.”
When it comes to environmental management, orchids are probably among the most demanding of all crops. Their requirement for light intensity and quality both vary, along with temperature, across the different growth phases over an 18-month production cycle.
Hortilux’s consultants worked with Ter Laak Orchids in the Netherlands for about three years to work out and trial the lighting strategy for an installation completed last year to largely replace the original HPS set-up.
“The company was looking for energy savings and greater controllability of not just the light environment but temperature as well, particularly during the cooling phase of production,” says Mr van der Valk. “Production is on benches that move through the different environments. We made an optimum light plan for each growing stage, including hybrid lighting for the stages where we needed to retain the heat from the HPS lamps.”
With the degree of controllability now becoming available, there is a risk of over-complicating the operation for growers, admits Mr. van der Valk. “It’s a question of flexibility versus cost,” he says. “Many regimes are now possible, but the question is, will you really make use of them?
“For example, you can switch off the green LEDs in the fixtures when no workers are in the crop [green light is needed by workers to ‘see’ what they’re doing], so the energy is used to power the more efficient red LEDs. But the overall benefit might be worth just 5-10 euros per year per fixture, as even the green light is of some use to the plant. It’s a question of working out if the extra technology is justified.
“That’s why it’s so important to connect with a company that understands what the crops need and will work with you on trials to find the right solution,” he says.
This article first appeared in the October 2023 edition of FloraCulture International.