Best grow lights are red, blue
Q. Does it matter what light I provide for plants if I grow my own from seed this year?
Nancy from Greenford
A. If you don’t have a greenhouse or a big window where you can put your seedlings, they need to be put under grow lights where they can continue to develop. There are many different types of grow lights available, so let’s review the type of light plants need and then what options there are to create this light.
Plants in nature use the light from the sun to power their lives. Plants use the same part of the sun’s output that we use to see. It’s called the visible spectrum. The visible spectrum is part of the overall electromagnetic spectrum produced by the sun. Seen through a prism, the visible spectrum is made up of colors ranging from red to blue, with the other colors found in between. To grow their best, seedlings need red light and blue light the most. The rest of the colors either pass through the leaf or are reflected off the leaf’s surface. For almost all plants, green light is reflected, making us see the leaves as green. The best grow lights should provide an abundance of red and blue light, without producing too much heat, which can damage the seedlings.
Here are the common bulbs you’ll find and why they will work or not work:
Incandescent bulbs: These are not a good choice for grow lights. These bulbs are too hot (90 percent of their energy is heat) and produce minimal amounts of blue light.
Halogen lights are a special type of incandescent bulb with the same problems.
High-intensity discharge: These type of lights, which include sodium vapor lights, produce the red and blue light and are long-lasting. But they also produce a lot of heat. These lights are used more often in commercial operations than in homes.
Florescent tubes: These are currently the main grow lights for homeowners. They usually come in 4-foot lengths and various diameters. You can buy special florescent grow lights that produce red and blue light. These lights are very good choices, but cost more than a regular tube. A less efficient, but also expensive way, to create a grow light is to use a combination of a cool light tube and a warm light tube. This combination produces some light in both the red and blue spectrum.
CFLs (compact florescent lights): These were designed as an energy-efficient replacement for incandescent bulbs. They produce much less heat that incandescent bulbs but their red light output is weak. They are not as good a choice as florescent tubes for grow lights.
LEDs: These are the future of grow lights. LEDs produce very little heat, last for a long time (up to 50,000 hours), and are designed to emit strongly in the red and blue spectrums. But until recently they have been expensive. Costs are coming down. LED lights can be found as stand-alone fixtures, track lighting and ribbon lights. Consider these first for growing your seedlings to save money and provide the best light.
For details on lights for seedlings, houseplants and more, visit http://go.osu.edu/rightlights.
Today’s answer is from David Sprague, OSU Extension master gardener volunteer. Winter hours for the Plant and Pest Diagnostic Clinic vary. Submit questions to the clinic at 330-533-5538 or drop samples off to the OSU Extension Office in Canfield.