Today’s light research helps determine the agriculture of the future (and into space)

To refresh your memory, why is light important for plant growth? Kathy Steppe: “Light is important for photosynthesis, the process by which plants produce sugars that allow them to grow. The sugars are formed from CO2 that the plant’s leaves absorb during the day. But the conversion of CO2 into sugars can only take place if the plant receives enough light. No light, no photosynthesis and therefore no growing plants. Or reasoned even further: no light, no photosynthesis, no oxygen, no humans.

Light intensity plays an enormous role in the growth of plants and crops. The difference between natural light outside and artificial light is enormous. “On a sunny day, the light outside is fifty times more intense than inside. But even on a gloomy autumn day, the natural light is ten times stronger.”

A lot of crops need a lot of light to grow, like the ones we grow in greenhouses. “We don't immediately put our plants under the lamp to grow at home, but growers do. Especially in winter, growers add light to extend the day for the plant, as if they were growing up in an eternal summer. Tomatoes and lettuce, for example, need a lot of light to grow well.”

At Ghent University, within the Agrotopia Chair*, we are researching, among other things, new LED technology to be used in high-tech, professional and vertical urban horticulture. We are also researching how we can make optimal use of artificial light. Which colors from the spectrum affect the growth and quality of the crops, and how can you best mix those colors? In that way, we can also eat delicious tomatoes from Belgian greenhouses in winter. Or control the firmness or vitamin content of lettuce leaves, for example.”

Greenhouses are often bathed in a purple glow at night. This choice of red and blue artificial light is not an arbitrary one, Kathy explains. “In sunlight all colors of the spectrum are present, with LED lamps we can choose specific wavelengths. Traditionally, the choice was made to use red and blue light and to adjust the strength according to what the plant needs at that moment in its growth. Red and blue light are absorbed by the chlorophyll in the leaves and stimulate photosynthesis, hence the choice of these colors. But pristine leaves absorb many more colors, we know. Finding the ideal light spectrum for plant growth is a hot topic within plant lighting research.”

To determine the right color combinations, Kathy and her colleagues are testing newly developed LED lamps from RAYN. “With these innovative lamps, we can select up to twelve wavelengths in the spectrum in order to discover which color mixes lead to optimal crops: mix the right light. The answers to this question are important for our future agriculture: think of vertical farming, or even growing wheat and vegetables on Mars. And also to get the energy bill of the growers down, of course (laughs).”

We can already grow food without natural light today, and the possibilities of controlling plant growth and quality based on light are constantly increasing. “Not only the mix of colors, but also the ratio of colors has an impact on the growth and development of the plant. There is such a thing as far-red light: depending on how high you set it in relation to red light, you can either make a plant grow very tall (fillet) or keep it very stocky. A lot is already possible, but we can gain even more knowledge.”

Mixing light is not only very important for plants, but also for the people working in the greenhouses, Kathy notes. “If you spend even a minute in one of those typical purple-lit greenhouses, everything is green when you come outside. So the impact on people is huge.”

And that’s very relevant when you consider another project Kathy and her colleagues are working on. “With the SpaceBakery consortium, a project supported by Flanders’ Food, we want to be the first to bake bread on Mars. That means growing wheat in closed conditions, for example in the rocket on the way to Mars or on Mars itself. With high-tech plant sensors and a unique virtual 3D plant model we are working on the best and most sustainable way of growing wheat in a closed biosphere.”

With this 3D model, Kathy and her colleagues can fully map the interaction between plants and light. “In this way, we are contributing to one of the greatest challenges of our current generation: producing more food on less land area and with fewer resources. The right light mix is also extremely important here, because if you have to grow that wheat in purple light, you experience stress as a human because of that. So finding the balance between human and plant is important in such extreme conditions.”

This article was produced in collaboration with Ghent University, partner of Lichtfestival Gent. Read more fascinating stories about Ghent University research on durfdenken.be.