Using Grow Lights for Seedlings or Indoor Plants
Grow lights are an incredibly useful tool for growing vegetables, herbs, and flowers from seed indoors. You can also use grow lights to keep houseplants happy and healthy, grow microgreens, or even to provide supplemental light inside a greenhouse. Plants rely on ample bright light to photosynthesize and live, after all. But, where to start? If you’re new to using grow lights, you’ve come to the right place!
This article will provide tips and information about using grow lights for seedlings and other indoor plants, including:
- A quick introduction on the benefits of using grow lights, including what types of plants and situations they’re most useful for.
- Part One: Considerations for choosing a grow light. We’ll explore the differences between LED and fluorescent lights, along with various ratings to look for like temperature, color, lumens, and size.
- Part Two: Best practices and common questions about using grow lights, such as how high to hang them, how many hours to leave them on, and safety considerations.
- Part Three: Finally, we’ll highlight a few popular and well-rated grow light options by category, such as “biggest bang for your buck” or the most versatile houseplant light.
By the end, you should have a pretty good idea on how to choose and use the best grow light for your individual set-up and plants! Then once you’re ready to start seeds, be sure to stop by our Seed Starting 101 tutorial for more start-to-finish tips. After all, not having adequate light is one of the top 9 seed-starting mistakes you can make!
Why use a grow light?
Plants rely on light to survive! Through the process of photosynthesis, plants harness energy from sunlight and convert it into chemical energy that is used to fuel their growth. In most cases, the amount of light a plant receives directly correlates to how vigorously it will grow. Using grow lights is an easy and excellent way to provide supplemental light and support plants where adequate natural sunlight is lacking.
Have you seen seedlings that are super tall, or even leaning towards a window? They’re stretching in search of more light. In the seedling world, taller doesn’t mean better! Without sufficient light, veggie seedlings get lanky, thin, and weak (also known as getting “leggy”) and are at risk of flopping over or breaking. Other indoor plants may struggle to grow, produce, or otherwise thrive to their fullest potential without enough light.
One of the best ways to prevent leggy seedlings and grow the most healthy, successful plants is by using grow lights inside. I hate to say it, but more often than not, a bright sunny window alone won’t provide enough light for starting seeds indoors. Especially in the winter months when daylight hours are already scarce; the time most gardeners start seeds for the spring and summer season ahead. The ample light provided by grow lights will keep seedlings short, stocky, and strong. However, bright windows and ambient light are typically sufficient for most houseplants.
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What plants need a grow light?
Certain plants require impeccable bright light for the majority of the day, described as needing “full sun”. Light-loving plants include most flower and vegetable seedlings, warm season annual crops like tomatoes or pepper plants, and hemp. Those guys will all benefit from a grow light while they’re indoors, no matter how naturally bright the space is. Succulents, cacti, microgreens, and herbs also enjoy full sun, but may be grown successfully inside without the use of grow lights as long as they’re near a very sunny window (ideally south-facing if you live in the northern hemisphere).
On the other hand, some plants can get by with lower to moderate light, such as pothos, philodendron, or sansveria – all popular houseplants. Ferns, orchids, and leafy greens can also happily grow in partial shade. Whether or not your houseplants will need a grow light depends on your space. In our home, we’ve found the ambient light from our windows is adequate for most common houseplants. However, plants in darker homes or interior rooms without windows will greatly appreciate a light! See our Houseplant Care 101 guide for more details on low, moderate, and bright light plant types.
Growing something unusual? Do a quick search on that plant’s unique light needs.
PART ONE: CHOOSING A GROW LIGHT
Grow lights come in all sorts of shapes, types, and sizes. So much so, that the various choices and number of grow lights on the market can feel overwhelming. Trust me, I get it! We’ve used several styles of grow lights over the years. LED, T5, multi-bulb arrays, single bulbs, with and without reflectors… the list goes on. Each of them has their pros and cons; it all depends on what you intend to use them for. And that’s the very purpose of this article – to help you figure it out!
Which grow light should I buy?
You’ll have to evaluate your unique needs to decide. As you read through the information below, consider the area and type of plants you want to use grow lights for. For example, how much square footage you need the grow light to cover. Will you need multiple lights, or one strong one? Can the style you’re looking at ‘daisy chain’ or connect several lights together? Is there a lot of headroom above your plant to hang a light high? Or, will it need to be kept fairly low, such as over trays of seedlings in between shelves?
The price for grow lights also varies widely, so do whatever fits within your budget. No matter what you choose, providing indoor plants with supplemental light will make them significantly more happy than going without!
Fluorescent vs LED Grow Lights
LED grow lights are all the rage these days! LED, which stands for light emitting diodes, are very efficient, and can also be quite powerful. Yet some old school gardeners swear by their classic fluorescent lights instead.
Note that there are many types of ‘fluorescent’ lights, including compact fluorescent lights (CFLs), basic fluorescent tubes, high-output T5 fluorescent tubes, and more. When it comes to fluorescent grow lights, T5s are considered the best choice for plants. T8 tubes aren’t quite as effective and bright, but are cheaper and can do a decent job for indoors seedlings or lettuce plants.
In general, a standard 45 or 60 watt incandescent light bulb (or LED equivalent) that you’d use in a household lamp fixture will not provide sufficient light for starting seeds or growing other plants that require ample light.
Differences between LED and fluorescents:
- LED lights are generally more energy-efficient than fluorescents, and therefore lead to lower electric bills.
- LED lights typically have a higher upfront cost than classic fluorescent tube lights, but may have a longer lifespan.
- Since they’re made up of dozens of diodes, LED lights come in a wider variety of shapes and sizes. T5 fluorescents are long slender tubes (e.g. “shop lights”) with either one or several tubes mounted in a ballast fixture.
- Per watt, LED lights give off more lumens of light. Therefore, a compact LED fixture has the potential to give off stronger light than a comparatively larger T5 fixture (but it depends on each light’s specifications). Some LED lights are weaker than T5s.
- It is usually recommended to keep LED grow lights suspended significantly higher above plants (feet) than T5 fluorescent lights, while fluorescents can be kept only inches above plants. This makes fluorescents more ideal for shelving systems with close quarters. Read each light’s specific recommendations!
Grow Light Ratings: Temperature, Brightness & More
As you shop for grow lights, you’ll notice various ratings for light temperature, Kelvins, watts, lumens, and more. This topic has the potential to get complicated (and often does), so I’ll try to keep it as simple as possible!
What color grow light should I get?
For growing seedlings indoors, choose a grow light that is described as “full-spectrum” or broad spectrum. I recommend the same for houseplants too. With a full-spectrum light, you’re getting a good balance of both blue and red light – and the closest thing possible to natural sunlight! Makes sense, right?
If you’re really curious to know the difference, cool blue light is great for promoting leafy green foliage but also regulates plant growth, keeping plants short and stocky. This is great for microgreens and seedlings (or plants in the ‘veg’ stage), but too much blue can also lead to stunted plants over time. Warm red light stimulates both vegetative growth and flowering, yet excess red light can make plants tall and lanky. Average household incandescent light bulbs emit mostly warm light, giving off a comfortable and cozy vibe – but not ideal for plants.
If the grow light temperature isn’t stated outright, look for its Kelvin rating. That will tell you the color of light it will emit. A full-spectrum grow light that closely resembles daylight will have a Kelvin rating of 5000 to 6500K. Cooler blue grow lights are rated around 4000 Kelvins, while warm or reddish lamps have even lower ratings – around 3000K. If you can’t find a full-spectrum light in the ideal Kelvin range that also fits your other needs (budget, size, availability, etc) a “cool white” light (4100-4500K) will also work well for germinating vegetable seedlings, growing microgreens, and raising young transplants.
Light Brightness and Lumens
Lumens is a measure of visible light that a source emits. The more lumens, the brighter and more powerful the light is. Vegetable seedlings and other “full sun” plants require about 2000 to 3000 lumens (at minimum) per square foot of growing space. So, if you’re growing just a single standard tray of seedlings, using a grow light that emits 3000 lumens is sufficient. Otherwise, do the math and scale up to a brighter light. Or use multiple light fixtures to provide a good canopy of light over a bigger space.
For example, consider a grow space that is 3 feet by 3 feet, or the equivalent to 9 square feet. Multiplying 9 by 2500 lumens (the average of the adequate range) tells us that a 22,500 lumen light would work well (or several lights that add up to cover that space). If math isn’t your strong suit, don’t worry. Most grow light manufacturers provide specs on the square footage they’re designed to cover.
Finally, keep in mind that wattage doesn’t dictate brightness! As we briefly discussed previously, LED lights give off more lumens per watt, so a low wattage LED (say, 20 watts) may give off even more bright luminous light than a 60 watt incandescent or fluorescent bulb.
Size of Grow Light
Consider two variables when it comes to sizing grow lights: the size of the actual light fixture, and the size of surface area it’s rated to adequately illuminate below the grow light. (See the section above about lumens and square footage too). Your growing area, ideal set-up, and number of plants directly influences the size of light that will work for you.
Are you growing trays of microgreens or seedlings on a shelf? Try fluorescent tube lights or strip LEDs suspended from the shelf above. Is there a dark corner in your living room where you’d like to keep a houseplant or two? You could use a single strong LED bulb or a sleek lamp fixture that blends in with your home decor. Panels or boxy light fixtures are ideal in a grow tent, starting seedlings on a table in your garage, or other larger area.
Some grow lights illuminate an area significantly wider than the light fixture itself. Others only adequately support the plants that are directly below the lights. If you aren’t sure, your plants will tell you! Seedlings on the outskirts of the light canopy will often lean inwards towards the brighter light. In that case, you may need a larger light. Or, you’ll need to routinely rotate the seedling trays below the light every day or two so all the plants have equal time in the spotlight.
Also remember that most gardeners pot-up their seedlings from small seed-starting cells to larger containers at least once (sometimes twice) before transplanting them outside. That move to a larger pot size will also increase the space the plants take up under a light! Meaning, you may need larger (or more) lights than you imagine when you first set out planting seeds!
PART TWO: USING GROW LIGHTS
How high should I hang my light above my plants?
A common question about using grow lights is how high to hang them above plants. The answer is: it depends! Usually, it’s recommended to hang high-output LED lights at least at foot (or higher) over plants. If they are too close, LED lights can and will burn your plants – known as ‘light burn’, and akin to a human sunburn. On the other hand, many fluorescent lights do best when they’re kept only a few inches above the plants.
When in doubt, follow the height recommendations provided by the light manufacturer. If that information isn’t provided, watch your plants for signs! Happy seedlings receiving adequate light will grow straight upwards, and stay fairly short and stocky. Seedlings that are hungry for more light will stretch tall and thin, and/or lean towards the brightest light source. If a light is too close and intense, burned leaves will turn yellow or brown, and sometimes have papery dry brown spots or tips.
In most cases, you’ll want to be able to raise the lights as the plants grow taller. This can be accomplished with an adjustable light chain, pulley system, or good old-fashioned string. Keep that in mind if you’re starting on a shelving unit that is already tight.
How long should I leave my grow lights on?
Seeds don’t need light in order to sprout. Steady warm temperature is more important for sprouting, such as that provided via a seedling heat mat. So, you technically don’t need to turn your grow lights on until after they emerge from the soil. However, you’ll want to provide light as soon as possible after germination. Freshly sprouted seedlings have the tendency to get leggy, fast! To play it safe, you could turn on the light a few days after you plant seeds, even if they haven’t popped up yet.
Once sprouted, most vegetable seedlings and other garden plants require at least 12 hours of good light per day, along with 8 hours of darkness. However, they’ll grow the best with around 16 to 18 hours of light. Houseplants are happy with less, where 6 to 12 of light is sufficient (depending on the type of plant).
To help keep our light schedule on target, we’ve found it incredibly convenient and useful to add a timer to our grow light set-up! The timer is set to turn the lights on around 6 am and off at 9 pm. You can find a full list of all our favorite seed-starting supplies here.
Grow light reflectors
Most grow lights come with built-in reflectors around the bulb fixture, helping to amplify and cast the light downwards. You can also create additional reflectors in your grow space! For example, one of my good friends starts her garden seeds using grow lights in a spare closet. Lining the back and side wall around the seedling trays with tin foil creates a reflective surface that bounces additional light back to the plants. The inside of specialized grow tents are usually lined with a reflective material for the same reason.
Can grow lights hurt my eyes?
The short answer is yes, so don’t stare at them. Any type of extra bright UV light can be damaging to our eyes. Blue light is also known to disrupt brain activity and sleep patterns. Working around colored grow lights can be generally uncomfortable to some folks (as opposed to those that emit white or “natural” looking light). We tried using an LED light that produced a very pink/purple hue one year, and being around the light gave me an instant headache. The plants that year also didn’t look nearly as healthy as they normally do with T5s.
Other safety considerations
Always be sure to mount or hang your light in a safe and secure manner that meets the manufacturer’s recommendations. Some grow lights give off heat. In general, LED lights are the least warm, T5 fluorescent tubes are also fairly cool but slightly warmer than LED, while T8 fluorescent, CFLs, or incandescent bulbs heat up the most.
Choose quality, reputable light brands that have good reviews. The light should be UL-listed or certified, meaning it has been tested to meet safety standards for electrical devices. If you’re using grow lights in an area that may be exposed to moisture (e.g. a humid greenhouse or one with ceiling vents), seek out a light that is considered waterproof or otherwise safe to use in that setting, and connect the light to a grounded outlet.
PART THREE: POPULAR GROW LIGHT OPTIONS
Biggest Bang for Your Buck
Several of the customer reviews for this Durolux T5 high output light fixture literally say “the biggest bang for your buck“! I haven’t seen many comparable units at this affordable of a price. With four fluorescent bulbs that emit a combined 20,000 lumens, this four-foot long shop-light style unit provides ample bright full-spectrum light for growing seedlings and more. It would be perfect hung over a table or mounted inside a wire shelving unit, and is equipped to connect several lights together if needed. Despite the strength, you can still keep them as low as 3 to 4 inches above plants without burning.
Looking for something a tad more compact? Check out the shorter two-foot version here.
Most Versatile Houseplant Grow Light
This sleek little LED grow light is ideal for houseplants that could use a boost! It can clamp onto a variety of surfaces (e.g. bookshelf or table) and has 3 swivel heads that move around as needed. The lamp provides a cozy warm-looking light but is indeed full-spectrum, and has 5 different brightness levels to choose from. It also has a built-in timer! This unit is so versatile, it could probably also work for small number of veggie seedlings (especially as supplemental light with a sunny window). The three-light version is shown below, and a smaller two-light option is available as well.
Best all-in-one set up for serious seed starters
Vermont-based Gardener’s Supply Co has created some awesome all-in-one grow light shelf kits! If you plan to start more than a handful of seedling trays, or have dozens of small potted plants, this could be a great option for you. After all, once you factor in the cost to purchase several quality lights plus a shelving unit, this snazzy 3-Tiered SunLite shelf would just about break even. The unit gets great reviews for being sturdy, mobile, easy-to-use with adjustable lights, and most importantly, effective at providing high quality light. I’ve also seen folks hang additional light over the unit and create a 4th upper shelf! The one shown below is the full-spectrum 6500K T5 fluorescent version. You could also step it up a notch and go for the ultra-efficient LED version.
Best Little Lights for Beginners
If you’re a brand new gardener, only need one modest light or two, or otherwise want to keep things as simple and inexpensive as possible, consider these options. First, check out this two-pack of 2-foot long T5 fluorescent lights. We’ve used the 4-foot long versions, and they’ve held up to many years of use. They aren’t the highest output lights in the world (2500 lumens per two foot bulb), but they’ll do the trick! Their mounting/hanging system is admittedly a bit wonky too. We had to MacGyver that. Another similar (perhaps brighter) option is this two-foot long box light from VivoSun.
If you’re a beginner looking to try LED lights on the other hand, MarsHydro is a really well-known brand. Here is one small and affordable full-spectrum light fixture they offer. It’s rated to light a 2 feet by 2 feet space of veggie seedlings. However, keep in mind you’ll need to hang LEDs much higher over your plant canopy. The one recommends to hang the light about 18 to 24 inches above.
Best overall LEDs for grow tents (& more)
Are you venturing into grow tents, or creating a DIY grow set up in your closet or shed? Horticultural Lighting Group (HLG) Quantum board lights are incredibly well-rated and powerful. The lighting portion of the lights are made by Samsung, and are quite popular with the herb-growing community (if you catch my drift). Yet you can use them for other types of plants and locations too of course! We have this model (shown hanging in our greenhouse earlier in the article), which is rated to adequately light a 3×3′ space of plants in veg, or 2×2′ area while they’re in flower. Note these lights can’t daisy-chain together, but they do have larger options. Another popular brand with similar specs and options to HLG is Spider Farmer.
And that concludes this crash course on using grow lights 101.
Well that was illuminating, now wasn’t it? I hope that this article turned on a few light bulbs in that noggin’ of yours, and helps you plan your grow light set up for the happiest plants possible! I also hope I made this somewhat complex subject nice and easy to understand. Please let me know if you have any questions or feedback in the comments below. Also, please help spread the love and knowledge by sharing or pinning this article. We appreciate you coming to us to learn something new. See you next time!
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Come learn all about using grow lights for seedlings or indoor plants, with tips on choosing lights, LED vs fluorescents, FAQ, and more!