If you’ve ever started seeds on your windowsill, you may have noticed that after the seedlings emerge, they lean into the window or towards the light source. This indicates that the plants are not receiving enough light. By far, the best option for light when starting seeds is to use grow lights. But there are so many types of grow lights – which are best?

The good news is you can start small. My first grow light setup was on an inexpensive folding table I bought at Walmart, and a 24″ suspended T5 grow light I bought on Amazon. I noticed a massive difference in my seedlings that first season – they grew taller with thicker stems and generally looked much healthier. Now I have a custom-made vertical rack of T5 grow lights and trays. With all that space, I start far too many plants each year, so I give a lot of seedlings away to friends and family each spring. But that’s a good problem to have.

What is a grow light?

A grow light is specialty indoor lighting of high intensity used to grow plants. They enhance foliar growth, produce thicker stems on seedlings, and produce the color and amount of light needed for flowering. Some grow lights are sold to light houseplants; some are used for indoor farming; others are for gardeners to start seeds and seedlings. This article will focus on the latter.

The first thing to understand is why your seedlings need grow lights. It comes down to light intensity and color temperature (warm or cool).

Light intensity

You may have a sunny window in your home at which you can start seeds. But if you’re starting more than a few plants, you’ll quickly run out of space. Unlike houseplants, seedlings need direct, intense light, not just a bright room. You can get away with starting a few on your windowsill, but you’ll need grow lights when you get past 3 or 4 plants.

What happens if plants don’t get enough light?

When seedlings lack enough light, they may not produce sufficient chlorophyll (green pigment), may become “leggy” (stems are long and thin and stretch toward the light source), may drop leaves, or may fail to produce flower buds. This leaves you with a less-than-vigorous seedling prone to disease or early die-off.

According to the University of Minnesota, “For seedlings that need to be planted very early, like peppers or tomatoes, more light is especially important. A seedling that is planted indoors just a couple of weeks before being transplanted outdoors can catch up outside, but a seedling that spends months indoors needs all of the light it can get to produce strong stems and to get a good head start on the growing season. For seedlings planted in a very bright window, a less intense supplemental grow light might be fine. But if you’re starting seeds in an area with little natural light, a higher intensity grow light will be a better fit.”

Color temperature

Sunlight contains a spectrum of colors known as wavelengths: ultraviolet, violet, blue, green, yellow, orange, red, and infrared. Plants use these different wavelengths of light throughout their life cycles to perform photosynthesis, flower, and fruit. In their early stages of development, they use more blue light. When flowering and fruiting, they use more orange and red. The color and intensity of light needed also varies by species. That’s why some grow lights are designed to emit specific colors that are beneficial for specific plants at different points in their life cycle.

“White” grow lights mimic sunlight by producing a full spectrum of red, blue, and green light, superb for producing vigorous seedlings of all types. Standard indoor lighting, like lamp bulbs, emit light wavelengths in a narrow band and are of low intensity. They typically will not be successful in growing most plants.

Current grow light setup with 4-foot T5 fluorescents in a vertical rack.

Types of grow lights for indoor seed starting

For seed starting and vigorous seedlings, most gardeners use T5 grow lights (a type of fluorescent bulb) or LED lights.

T5 grow lights

T5 grow lights are fluorescent bulbs and one of the most common types of lighting for starting vegetables, herbs, and flowers indoors. These are not like the fluorescent lights in an office building – T5s produce twice the intensity of light as standard fluorescent bulbs. T5 grow lights require a ballast to control their current and will only fit into a specific type of pin-type light socket. Due to the heat they emit, they should be suspended at least one inch above the plants, to avoid foliage damage.

LED grow lights

LED grow lights are sold in arrays that contain bulbs that emit different colors. Each LED bulb can only produce a single, narrow range of color, so LED bulbs must be mixed together to provide the proper light spectrum for plant growth. On the other hand, this also allows manufacturers to customize each model’s color wavelength so that the gardeners can dial in more specific lighting requirements depending on the plants they are growing. LEDs use less energy than T5s, but produce a lot of heat, so they also must be suspended at least 12 inches above the plants.

Setting up grow lights is easier than it sounds, once you carve out a space and get the lights set up. This is a gardening decision you won’t regret as your seedlings will be more vigorous than growing them with light from a window.

References: Wikipedia: Grow Light, University Of Minnesota Extension, What types of grow lights should you use for starting seeds indoors?, University Of Maryland Extension, Grow Lights For Starting Seeds Indoors.