Most commercial greenhouses are growing vegetables on vertical high-wires these days, and the demand for artificial lighting has been increasing for years. To help greenhouse growers grow their crops even more efficiently, Philips lighting is always searching for the most effective solution. Ten years ago, we introduced a new type of lighting called interlighting, followed recently by a high-output version. By now, this way of applying light to plants has proved itself numerous times, and we’d like to share what we’ve learned along the way. 

Many high-wire crops like cucumbers and tomatoes are grown using traditional HPS (high pressure sodium) grow lights above the crop. But with the arrival of LED interlighting in 2008, Philips lighting began researching the effects of placing LED lighting within the canopy of high-wire plants to improve crop yield and quality. These trials showed that placing LED interlighting within the canopy of high-wire plants allows you to focus growth-stimulating light on parts of the crop that are normally darker, so that the leaves have an even greater impact on fruit production. This can significantly improve the quality and yields of crops.

Back in 2010, Dutch tomato grower Jami and his growers' cooperative were closely involved in these trials, and the positive results convinced them that intercanopy lighting was the way to go. In 2012, growers cooperative Van Nature (where Jami is one of the members) invested in a Philips hybrid lighting system, combining HPS lights with a double line of LED interlighting which was installed in Jami's greenhouse. Their greenhouse was too low to accommodate sufficient HPS lighting to support year-round production. That meant that this hybrid lighting solution was the best option for them. At that time, it was a 'forced choice'. Ask them now, and based on their experience and results with LED, they wouldn't want anything else. 

The light spectrum of the LED intercanopy lighting has been optimised to maximise photosynthesis. Red light is the most effective for photosynthesis, so our LED interlighting module has a lot of red light, with a bit of blue to ensure the correct plant development. This module is the result of our research carried out since 2008, which tried out various light spectra for high-wire tomato crops. The spectrum combines light spectra that promote growth and energy efficiency. This light spectrum was installed at Jami in 2012 on a commercial scale, and many growers in other countries have subsequently followed their example. These results prove that our years of research are now paying off for growers. 

Leaves are the 'growth engine' of a plant. In a high-wire crop such as tomato, leaves are distributed over a height of 2-3 metres. When lit from the top, either by the sun or by artificial lighting, the top leaves receive much more light than the lower leaves. This means that the top leaves are operating at full production capacity, but the lower leaves are not. LED intercanopy grow lights add light at the right place at different levels along the plant, so that the leaves in that area become producers instead of being consumers. Since the lights are applied within the canopy, all light is absorbed by the crop. No light is lost due to reflections or to the floor. At Jami, there are two rows of interlighting to provide sufficient light, distributed evenly over their plants and to fit the low height of their greenhouse.

At Jami, more light within the canopy produces higher yields as the chart below shows. From the moment they switched on the lights, their production has been steadily increasing. Each year, the production continues to rise, and Jami continues to learn and improve.

Because you can provide light within the plant canopy, you can reduce the amount of HPS lights on top of the plants. This also reduces the heat produced by the HPS lights, giving you more control over the greenhouse climate. Due to a better climate at the top of the plant and optimal light distribution across the entire plant, a tomato grower like Jami can produce more vegetables per square metre during the winter months. During periods when growers who have only HPS lighting have to switch off the LED lights due to too much heat, Jami can use their full lighting capacity, which results in extra production. Even outside the normal lighting season, Jami uses the LED interlighting to supplement light on dark days to maintain their growth and production.

Michel Zwinkels at Jami says, "Even a somewhat weak truss becomes strong as soon as it reaches the LED interlighting. The light acts as a tonic to strengthen the truss."

Based on input from growers around the world, we introduced our new Philips GreenPower LED interlighting high output version in January 2017. This new generation product is ideal for growers who want to apply the highest amount of light possible to get the highest yield possible.