The grow light industry is, well, growing like a weed. From Arctic greenhouses and urban gardens to legalized marijuana farms, the lights we use for growing plants indoors have sprouted into a multi-billion-dollar industry.
Closer to home, on our windowsills and coffee tables, we’re becoming evermore fascinated with our leafy ficus, stoic cacti and aromatic oregano friends.
“We know from research that keeping indoor plants has many benefits, such as reduced anxiety and stress, improved productivity and focus, and even improved healing,” says Leslie F. Halleck, an author and certified professional horticulturist.
“So in terms of wellness, bringing some nature indoors can have a very positive impact on our lives. Beyond the mental benefits, plants bring so much dimension, aesthetically, to our homes and offices. Plants literally bring our indoor spaces to life.”
It turns out some of those plants would also love a grow light, at least for part of the year.
What Is a Grow Light?Grow lights allow us to cultivate various plants indoors, regardless of the season or available sunlight. They use a specific ratio of wavelengths, mostly in the red and blue spectrums, which are ideal for helping plants photosynthesize.
Their effectiveness depends on:
Which type of grow lights you use depends on what you’re growing. For some plants, it can get pretty complex. Here are the basics.
Here are the three main types of lights for indoor home use: Fluorescent, low-power LEDs and high-power LEDs.
Fluorescent LightsThese are the old-schoolers of the grow light world. They owned the show until the flashy LEDs strolled onto the scene. They don’t last as long as LEDs, are bulkier and less sustainable, but they are easy to find and still a worthy option.
Halleck recommends HO T5 fluorescent lamps, which produce less heat than the old bulbs and are more energy efficient. Handle them carefully; some fluorescent lamp ballasts contain mercury. If you have a fluorescent fixture but want LED lights, some LED replacements look like fluorescent tubes.
Pro tip: On fluorescent lamps, there’s a ballast inside the light fixture that generates heat, so one section will be hotter than the rest. This means sometimes the plants under the ballast will show heat stress.
These are easier on the electric bill and last longer than fluorescents, but the quality ones are often more expensive. The challenge with LEDs is figuring out if the intensity is adequate, because watts are not an accurate measure with LEDs.
“We can measure how many photons of photosynthetically active radiation (PAR) are being given off by a light, and that’s linked to wattage, but using wattage is really not a useful spec,” says Jonathan Ebba, a field specialist with the University of New Hampshire Cooperative Extension.
“Reputable manufacturers will publish the intensity information [of their grow light] in terms of moles of useful photons delivered per square meter per second. A mole is a number, a six with 23 zeroes. It’s a way we count photons.”
Low-power LEDs are the inexpensive ones that pop up first like a field of dandelions in your online purchase search. They’re often good enough for foliage houseplants or small succulents. But they’re not much good for plants that need intense light, like tomatoes, citrus and herbs.
Many emit a pink or purple color, so if you don’t want that in your living space, Halleck recommends looking for ones with a full or broad spectrum of white-colored light.
High-power LEDs are ideal for edible plants, larger floor houseplants and actually pretty much anything that isn’t a windowsill plant. To get ample light intensity (PPFD), you mostly get what you pay.
“There are a lot of cheaply made grow lights on the market these days, so I typically recommend buying lamps made in the U.S.” says Halleck. “I find quality and longevity is better, as well as care of shipping and customer service.”
Other household lights are not so good for growing plants. Incandescents get too hot and their spectrums are heavy with yellows and greens, which do not promote photosynthesis well. Halogen lights put off excess heat and are poor with energy efficiency.
Note: Another consideration is light spectrum. Lights are broadly divided into cooler and warmer spectrums. Cooler lights (>5,000K) better support leafy growth while warmer lights (<5,000K) encourage more flowering. "However, most plants will grow just fine under a balanced broad spectrum grow light," says Halleck.
How To Use Grow LightsSucceeding with grow lights will be a process of trial and error. So have fun, experiment and don’t get discouraged too quickly.
Here are a few steps to help you find the best grow light:
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