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Lighting upgrades turn UAF greenhouse pink

By Laura Weingartner

Keen observers might have noticed that the orange glow from a University of Alaska Fairbanks greenhouse recently shifted to pink.

The color change came with lighting upgrades this summer at the Agricultural and Forestry Experiment Station Greenhouse on the West Ridge of the UAF Troth Yeddha’ Campus.

Meriam Karlsson, UAF professor of horticulture, said many of the greenhouse's old high-pressure sodium lamps were replaced by light-emitting diodes, commonly known as LEDs.

Sodium lamps were the standard greenhouse lighting source for many years, partly because other options were limited. Improved technology has made LEDs affordable and more than twice as energy-efficient as high-pressure sodium lamps. LEDs also give researchers more control over the spectrum of light plants receive.  

The spectrum in the new greenhouse LEDs is more balanced than the sodium lamps, providing blue, green and red wavelengths. Many of the new panels in the greenhouse are red, an important color for photosynthesis and plant growth. These lights give the greenhouse its pink glow. 

Sodium lamps use an electric current through a tube (bulb) containing sodium and other gases in a vaporized mixture. When heated, sodium emits light at a wavelength of about 589 nanometers, which appears orange to the human eye. The spectrum of light plants receive from these lamps mainly consists of yellows, reds and oranges, with minimal blues and greens. 

Since blue light is also important for photosynthesis, sodium lamps are mostly effective as supplemental lighting rather than the sole source of light for plants.

Karlsson researches how manipulating light can increase crop yield and maximize plant growth, flowering or fruit production. Plants' response to lights varies depending on the plant and its life stage. She adjusts light intensity, color and day length, for example, to prevent flowering in spinach while maximizing leaf production.

Growing protocols for light have been developed for years for various greenhouse crops and plants, but light has often been the limiting factor, as the older technology couldn’t provide enough.  

“We can now better simulate various light levels, including what can be expected (or higher) during the field season,” Karlsson said. 

Her research can be used by Alaskans working to extend the growing season. For food to be produced during the winter in Alaska, controlled environments, such as greenhouses, hydroponics, and vertical and indoor farming, are necessary. Energy for heating and lighting is often an issue for these facilities producing food during the winter in Alaska. 

Upgrading to LED lighting can inform growers about the cost of the swap and how well it works in the cold winter months of the Interior. The fun pink color is just a bonus. 

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