An Energy-Efficient Endless Summer for Plants

COPENHAGEN — Plants need food, water, red and blue.

Red and blue light that is, according to John Erland Ostergaard, a professor at the University of Southern Denmark, who has come up with a lighting system based around LEDs that he says could drastically cut the power consumption in greenhouses. (We met at Copenmind, a technology conference taking place this week in Copenhagen. Also to note, Toyota downplays lithium-ion batteries and an Irish scientist makes plastic with bacteria.)

In the system, microcontrollers adjust the amount of red and blue light, the portion of the light spectrum that plants need to grow to ensure optimal growth, coming from the LEDs. The amount of red and blue light is tweaked according to time of day, plant species, and time of the year. It can also compensate in case clouds or excessive sunlight.

In a demo, he puts he hand over a sensor to simulate sun. The LEDs start giving off more intense light. He removes it and the light level goes back down.

The overall effect is an endless summer. In one experiment, a rose grower was able to grow roses in Denmark in winter in 12 weeks, the length of time it takes to grow them in the height of summer. Typically, roses in the winter take 14 weeks to grow. Ostergaard’s group has studied different types of plants — tomatoes, cucumbers — in a closed environment and measured things such as the CO2 and oxygen exchange to try to determine how to vary light intensity during a typical day to maximize growth.

Just as important, the power consumption was throttled. The LEDs consumed only 71 watts—an ordinary grow light would have consumed 510 watts. In some cases, greenhouses can cut lighting power by 80 percent, he said.

The power consumption comes because the LEDs only put out beneficial light. Ordinary grow lights put out a broad spectrum of light—orange, green, etc.

“The LEDs only put out the light that is needed,� he said.

Varying the amount of red and blue light can also impact the overall quality of the plant. Increasing red light can make the plant more compact — the stems stay closer together when growing.

You can expect to see something like this advertised in the back of “High Times” soon.