But such lighting is still four-to-five times more expensive to install than conventional high-pressure sodium (HPS) lighting of the same luminosity, equating to an average of 50 per cent more costly per year. Research has so far shown "barely higher production" using LEDs, according to programme representative Dennis Medema.
Stockbridge Technology Centre facility manager Dr Phillip Davis told the Tomato Growers Association conference that a four-way glasshouse trial investigating different lighting formats on tomatoes at the North Yorkshire research station has so far failed to show clear benefits of any one format.
"Through the winter there was a similar yield in all four compartments (HPS only, LED only, a hybrid of the two and LED under diffuse glass). The LED-lit crop had a lower flowering rate, due to being cooler, but had higher head density. We had to add more heat into the LED compartments, so the total energy use was about the same. Tomato plants can only make use of light when it's warm."
But Philips Horticulture LED Solutions director Udo van Slooten said at the conference: "In lettuce you can use LEDs to raise light levels to give you more product per square metre, whereas too much HPS gives you tip burn. We are looking with (breeder) Rijk Zwaan at how you adjust growing for this. Already there are some projects of more than a hectare just of lettuce."
In closed LED-only growing, meanwhile: "Projects are getting more serious, especially in the US and Japan. You can really control the nutrition levels in a crop like lettuce. The big distribution chains are picking up on this." Last year, 3,100ha of Dutch production horticulture was lit by LEDs, accounting for three per cent of the total area employing supplemental lighting.