Two Dutch growers start trial with vertical LED interlighting system

Vertical fixtures with two exposure modes: red blue and far red. This is how the staff of Lohuis Lighting sees new opportunities for LED lighting in horticulture. The first tests are conducted at Noordhuys Tomatoes and cucumber grower Jan Reijm in Holland

It actually looks quite bizarre. Between the cucumber plants of Jan Reijm fixtures of a meter long are placed that emit a very soft, red glow. During the day you could hardly see it. Even at night, when the lights are switched on, it is hardly visible. "It is far-red light, which human beings notice in a reduced manner," says René Grootscholte of Lohuis Lighting, the company that developed the light fixtures. "We use the light as post-exposure. The other exposure mode emits a red-blue spectrum."

Lohuis Lighting has a long history in lighting. Since the 70s they have been active in making specialty light sources. "But with the advent of LED that demand has dried up. LEDs are generally accepted as a light source in various applications," said Anton Lohuis, owner of the company. Also in the horticulture sector LED made great strides forward. "But we could not foresee the swiftness with which it took place. Ten years ago I was asked if LED lighting would replace the HPS, the standard assimilation bulb in horticulture. Then I thought that I would not live to see that," he says. Nevertheless, this switch-over is now on-going. Since at Lohuis we were already very familiar with various light sources, the move to horticulture was small. 

But is this not a market segment in which many competitors are active? "Maybe so," says Anton. "But there are not many companies that are able to develop their own fixtures. We have chosen to do so." The starting point is that Anton wants to be the production cost of LED to be competitive. "We have now reached the tipping point: LEDs need not be more expensive than HPS lighting."

Lohuis recruited René Grootscholte for the development of the fixtures. After reading everything about exposure, Grootscholte noticed something unusual. "A plant mostly absorbs light on a specific plant part of about 1 meter in length, but with horizontal fixtures in reality only one single strip is illuminated. This is not an optimal exposure for the growth potential." Based on this conviction René developed vertical fittings of 1 meter length that provide light all around.

A second point which makes the light fixtures stand out are the lamps with two colour modes. One switch position provides red-blue light, the second far red. "To switch on those two together does not make sense: you would need an enormous amount of far-red light if combined with red-blue," says René. "This was evident from testing, including from the Wageningen University and Research (WUR). Just one hour of additional exposure with far-red light, puts the plant in generative mode." This winter the first trials started with the lights. At Noordhuijs Tomatoes we are employing a fixture that spreads light on two sides at an angle of 150 degree.

At Jan Reijm on 540m2 of cucumbers we use a different light fixture, that thanks to adjusted shape and different technique spreads the light almost 360 spread around in a diffuse manner. It is expected that the use of mMols will be more efficient.

Total exposure for the cucumber testing is 95.6 mmols/m2, this requires 9 light fixtures per 5m2. The light fittings can be raised during the growth season.

The tomato testing is under way since the end of October, the cucumbers since December. The first cucumbers at Jan Reijm were harvested this week and the quality is satisfactory. But not only that, the expectation is that the two high-wire growth will generate in excess of 300 cucumbers. “This season we monitor all aspects and this would mean a large step forward”, according to René. “Even with the best and most costly available LEDs we can design a fixture that after 10 years will be competitive with HPS lighting.”