For many years High Pressure Sodium (HPS) lamps have been the horticultural industry standard for lighting glasshouse production. However, there has been steady growth in the uptake of LED lighting systems, with many growers now investigating the new opportunities they present.
LED lighting trials in an open glasshouse environment
One application of LED lighting is being investigated by researchers at Stockbridge Technology Centre (STC), a LEAF Innovation Centre in North Yorkshire, UK. They have been looking at moving horticulture units into highly insulated enclosed warehouses lit by LED lighting systems, often called Urban Farms.
The benefits of production in this way all relate to control – control of the temperature, lighting, water and even to some extent, control of pests and pathogens due to the closed system. Large savings can be made in heating costs in heavily insulated buildings, compared to glasshouses, and these savings are expected to outweigh lighting costs, especially as each decade LED prices have fallen by a factor of 10 while performance has grown by a factor of 20 (this phenomenon is known as Haitz’ Law).
However, LEDs don’t just have benefits in an Urban Farm system. Lincolnshire Herbs and Swedeponic have been trialling LEDs extensively during the 2012/13 winter in Sweden and the Czech Republic on their herb crops in glasshouses. They found that when LEDs were used at the same intensity as their conventional HPS lighting, they could make energy savings of 48%. This is a really significant saving so I was keen to ask Patrick Bastow, who ran the trials, whether there were any downsides to the system:
“No we didn’t see any downsides. Nor did we see the need to increase the heating in the LED crops to cope with the loss of infrared heat that you normally get with HPS. However, this could be different for different crops.”
A current problem with LED lighting systems is the cost of the installation, although this is expected to fall in the coming years. With energy savings of 48%, Patrick thinks it could still be several years before an investment would start to pay off.
“It’s looking at around 8 years before we get payback where we run lamps at 3,000 hours per annum such as in Sweden. When we run lamps for less, in the region of 2,000 hours such as in the UK, then payback will be higher. At this level of payback the technology is still a little away from commercialisation – but affordable for trials.”
There are benefits aside from the financial ones, however. Light pollution is a major issue in planning permission and with local complaints. LED lighting is more directional, which means there will be less light spillage. Although this hasn’t been proved on a commercial scale, in theory it makes perfect sense. Of course, any light spillage means that light is not getting to the plants and is lost, so being more targeted could have benefits in efficiency too.
Part of the LED4CROPS facility at STC showing the multi-tier growing racks illuminated
with Philips Greenpower LED lights.
There are three colours of light (red, blue and far red) which efficiently drive photosynthesis and stimulate the plant to control morphology and flowering time. LEDs used for horticultural applications emit these colours, but the amount of each colour and how many hours the lights operate can be varied according to ‘light recipes’. Specific recipes for different crops are being identified in research at STC. Work already carried out in the facility has shown that plant morphology can be greatly altered by changing the ‘light recipe’. However, controlling the ‘light recipe’ in an open glasshouse environment will need more work. In Patrick’s trials they achieved almost the same results using three different ‘light recipes’.
So are LED lighting systems a sustainable solution? Patrick certainly thinks so, “Yes they will be. We also found that by using 16% more energy than we use with our current HPS system, we could get up to 250 µmols more light and grow the crop faster. This will mean more production in less space and remove the need to build more production area. This is still work in progress but it is another strong financial argument for LEDs on top of payback from energy savings.”
“I would recommend that all glasshouse growers buy a few LED lamps and run some trials, it’s an exciting new tool and growers need to start seeing what it can do for them.”
If you’re thinking of making the transition to LEDs in existing glasshouses or to Urban Farming systems, Stockbridge Technology Centre will provide UK growers with the expertise and knowledge needed to assess the potential benefits, contact Phillip Davis for more details.
What do you think? Do LEDs represent the future for sustainable horticulture? Let us know in the comments section below.
With thanks to Patrick Bastow and Stockbridge Technology Centre.