Doubling of light level in lettuce cultivation

Desmet grows Salatrio, red and green Oakleaf lettuce and Lollo bionda on water gutters throughout the year. Whereas in his other greenhouse he already has 45 µmol per m2 using HPS lamps, he is now opting for 80 µmol per m2 using LEDs. He has installed Philips GreenPower LED toplighting DR/W/LB* above his crops. This means that, particularly in winter, he can achieve higher production levels than before. Philips LED Horti Partner Mais Automatisering installed a total of 2,610 LED toplighting modules over an area of 14,460 m2.

The lettuce grower is aiming to reach the top and get as much production as possible from every square meter. This is why he has not gone for a hybrid installation. With hybrid lighting you still get 50% radiant heat. This heat causes an excessive rise in the temperature in the greenhouse, making the climate unsuitable for lettuce cultivation. Danielle Smits-van Tuijl, plant specialist at Philips, explains where the opportunities are: “Although radiant heat contributes to plant temperature, you can also achieve higher temperatures in other ways. With HPS lighting you have no choice, since the lamps automatically give off radiant heat. With LED lighting you have the option of separating light and heat and controlling them individually. This is why with LED lighting the number of lighting hours can be increased further and a higher light level can be achieved.”

LEDs have paved the way for higher production figures, since the lighting can also be used at times when outside conditions are too ‘mild’. The plants receive light energy at the right moment. Desmet therefore anticipates an increase in production due to the higher light level, more lighting hours and greater plant density. The lettuce is expected to be more compact and firmer and have a better red coloration than the product grown in the department where HPS lighting is used.

In addition to Johan’s enthusiasm for the new lighting technology, positive research results were the decisive factor for him in having Philips GreenPower LED toplighting installed.

For Desmet, Philips was the logical choice: “From the start I believed in the potential of LEDs and had the greatest confidence in Philips’ know-how,” he explains. Last year’s lighting trials at the Testing Station for Olericulture (PSKW) in Sint Katelijne Waver were the initial step. The Testing Station compared HPS lamps and Philips GreenPower LED toplighting, with a light level of 50 µmol/m2. In the winter the red lettuce varieties showed better red coloration in the LED greenhouse. The crop also suffered less from tipburn, the red Oakleaf lettuce remained more compact and the Lollo rossa was significantly heavier.