Owner Michel Zwinkels says: “People often underestimate the added value of interlighting.”

Late 2023, Signify was commissioned by its recurring customer, Jami Tomatoes BV, the Netherlands, to provide a full LED installation, consisting of Philips GreenPower LED toplighting compact (TLC) and Philips GreenPower LED Interlighting. The installation provides up to 250 µmol/m2/sec of additional grow lighting. "The old hybrid system from 2012 was due for an upgrade," explains owner and director Michel Zwinkels. "The new installation has a higher light output and uses less power. That way we can achieve optimal energy usage."

Zwinkels and his co-director Jip van 't Hof have always liked the combination of toplighting and interlighting. "With a high-wire crop like tomatoes, you don't want light just at the top of the crop, but also on the lower leaves and ripening trusses," says Zwinkels. "The combination of toplighting and interlighting produces more photosynthesis than just toplighting, at the same light level. In addition, the light and the little extra heat that becomes available lower in the crop are good for the crop activity, speed of ripening and fruit quality."

Of course, the investment is higher because you're actually using two installations rather than one. This would make interlighting seem the somewhat less obvious choice, but people often underestimate the added value, according to Zwinkels. "We are sure we'll more than recoup those extra costs. We never hesitated about interlighting."

A little more light, 40% savings
In terms of the lighting level, Jami Tomatoes BV has made progress. The new system, which was installed by Hortipar, provides 110 μmol/m2/sec of interlighting and 138 μmol/m2/sec of toplighting. In the old set-up, Zwinkels had 110 and 115 μmol/m2/sec available, respectively. One immediately noticeable difference is that there is now one line of interlighting, whereas the previous configuration included two lines, one on top of the other. Account manager Edith Post, who supervised the project from Signify, says: "The new generation of Philips Greenpower LED interlighting fixtures is more efficient and powerful than the generation that Zwinkels started with in 2012. You can easily do with just one line." "One line of interlighting instead of two also costs less," adds Jip van 't Hof, co-director, "So, that wasn't a hard choice either."

A little more heat
Both companies knew that the switch to full LED would have an impact on the dynamics in the greenhouse climate, especially in terms of managing the humidity. "You lose some radiant heat from above," Van 't Hof continues. "To keep the crop active and to remove enough moisture, we need to introduce a little more heat through the grow tube and the pipe rail heating. As soon as we need to actively remove moisture, we open a gap in both screens. The moist warm air is then drawn upwards, where the moisture can condense against the deck or exit through small window openings. Of course, some heat is lost in the process, but we don't want to compromise on growth rate or fruit quality. It is all calculated and factored in beforehand."

Favorable energy usage
Jami Tomatoes BV has over 6 hectares of growing area, half of which is under lights. At full capacity, the new lighting installation consumes 40% less energy and supplies about 10% more light than before. Zwinkels explains the impact this has on his company's energy usage. "In the past, at peak load, we had to generate 3.8 MW of electricity via the CHPs. That resulted in a structural heat surplus, partly because the HPS lamps also gave off heat in the greenhouse. In the current set-up, we don't have to use the lighting as long as before because the light output is higher. In addition, full LED is much more efficient. At peak load we need only 2 MW, which means far fewer CHP hours are needed. Now that we're also giving it a little more through the grow tube and pipe rail, the heat surplus has been eliminated. So our energy usage looks a lot better, and we hope to enjoy that for a long time to come."