LED grow lights should be at a distance of 12 to 36 inches from plants, but the ideal distance will vary. It will depend on the type of plants you intend to grow, how much ambient light your plants are already getting, and the wattage of your LED grow lights.
There’s one more factor that influences the ideal distance. That is your plants’ current growth stage. Seedlings, for instance, require lower intensity light as they’re too vulnerable in this starting stage. That isn’t the case with plants in the vegetative stage, which respond better to intense light.
In this article, we’ve explained all the factors mentioned above in detail. Read on if you’re interested in finding out how each of these factors will influence how far (or close) the LED grow lights should be from your indoor plants to unleash their growth.
How Far Should LED Grow Lights Be From Plants?
As stated above, multiple factors influence the answer to this question. They include your plant’s growth stage, the amount of natural light your grow area is already getting during the day, the type of plants you intend to grow, and the wattage of your LED grow light bulbs.
Let’s discuss all these factors in detail.
1. Your Plant’s Growth Stage
Experts divide plant growth into three different stages – seedling, vegetative, and flowering. Plants still in the seedling stage barely start growing their first pair of leaves. During the vegetative stage, they collect resources they’ll later on require for flowering.
Flowering stage is the last stage of growth for most plants. Some farmers also refer to it as the blooming or the fruiting stage. That’s because it’s in this stage that plants produce flowers (or vegetables). You’ll be able to harvest your plants at the end of this stage.
Here’s how your plant’s growth stage will determine the ideal light distance:
How far should LED grow lights be from seedlings?
Depending on the size of the LED grow light, it should be at a distance of 24 to 36 inches from the top of the seedling’s soil. Seedlings are highly delicate, and if you expose them to too much light, their soil might dry out, hurting your plant’s growth prospects irreparably.
How far should LED grow lights be from vegetative plants?
Hang the LED grow light less than 10 inches away from the top of the leaves of plants in the vegetative stage. Plants in this stage need greater intensity to use photosynthesis and to mature quickly. Without enough light, their stems and roots might not develop, leading to poor yield.
How far should LED grow lights be from flowering plants?
During the flowering stage, LED grow lights should be placed between 16 and 36 inches from the top of your plant. Sure, moving the grow light even closer might maximize photosynthesis. But too much photosynthesis might lead to horizontal growth, which is something you must avoid.
2. Your Grow Area’s Light Level
How much ambient light – aka sunlight – your plants are already getting will also determine their ideal distance from artificial LED grow lights. After all, if you’ve already placed your plants in the south-facing window (where they’re getting all the light they need), why bother with artificial lighting.
Conversely, if your grow space affords minimal natural light to your plants, you’d be better off investing in a full-fledged LED lighting setup. If your plants remain in the dark for a few days, their chances of realizing their growth potential will decline.
Use these three categories to see which spot you’ve chosen for your plants:
Bright Light
Well-lit spaces are those where everything inside looks bright. You can clearly see every item in the room, and the presence of sunlight discourages the infestation of pests. Yet another attribute of well-lit rooms is that they appear bigger than their actual size.
Such rooms mostly have south or south-west facing windows that allow plants to receive sunlight for the entire day. If you think you’re growing your plants in a brightly lit room (and the sun shines almost every day in your area), you could do with a minimal wattage LED light.
Medium Light
Partially lit spaces either have east- or west-facing windows. Such openings allow the plants to come face to face with natural light for one to two hours in the morning and late afternoon. Or their south-facing windows are blocked by blinds or curtains.
If you’re using such space to grow plants, remember this rule of thumb: install 20 to 30 watts of LED lights per square foot of the growing area. The lower end of this range is for seedlings and flowering plants, as they need less light than plants in their vegetative stage.
Low Light
Are all the windows in your grow space north-facing? Is an adjacent building blocking the sunlight from entering your grow area? Such grow spaces can be categorized as low-light spaces. A similar classification applies to apartments located on lower floors or facing the backyard.
Keep in mind that if your grow space is so dark in the middle of the day that you can’t read a book without turning the light on, then it’s too dark for any indoor plant to survive. You’d be better off moving to a medium or, if possible, a brightly lit room.
3. Type of Plants
Some plants not only survive but also thrive in darkness. They are aptly termed as ‘low-light’ plants by indoor farmers. That isn’t the case with medium light and high light plants, for whom more than four to five hours of darkness can be deadly.
Here are the examples of low, medium and dark light plants.
What are low light plants?
Low light plants are those that don’t need sun. Examples of popular low light plants include bromeliad, Chinese evergreen, cast iron plant, dracaena, and English ivy. Other plants that can thrive in low light conditions include maidenhair ferns, parlor palms, and peace lily.
While these plants can easily grow in rooms with no windows or north-facing rooms, you should still leave the artificial lights on for at least 12 hours a day. If that isn’t an option, consider moving them to a brightly lit room for a days at a time.
What are medium light plants?
Medium light plants thrive in rooms that don’t get much sunlight each day. They could add a touch of greenery to a closed space and create an eye-catching environment for guests with their appearance. Example of medium light plants include alocasia, African violets, anthurium and croton.
Unless these plants are getting as much sunlight as they need, you need to provide them with an adequately powered LED light. Make sure that the distance between the plants and the grow light should not be less than 20 inches, or else their leaves might burn.
What are high light plants?
High Light plants do extremely well in sunny windows. They are a great choice if your grow room has lots of south or west-facing windows. Make sure you place these plants within 6 feet of a window as they need a lot of sunlight to realize their growth potential.
Examples of high light plants include white bird of paradise, yucca plant, ponytail palm tree, columnar cereus peruvianus cactus, and ming aralia plant. Some people also classify the croton plant as a high light plant, but we suggest you keep it for your medium-lit rooms.
4. Your LED Light’s Wattage
Your LED light’s wattage will also influence its distance from your plants. Higher-wattage LED lights should be placed further from the plants, lest they burn or scorch their leaves. However, you can move lower-wattage LED lights close to the plants without endangering them.
Keep in mind that LED lights emit lower heat than other grow light options on the market. An estimate by the US Department of Energy states that they only turn 5% of the electricity into heat, compared with 80% of the energy CFL bulbs convert into heat. So you can place LEDs much closer to your plants.
Here’s a quick guide to help you out:
- If you’re using 200 to 399W LED light, place it at a distance of 12 to 20 inches from your plants
- If you’re using 400 to 599W LED light, place it at a distance of 20 to 27 inches from your plants
- If you’re using 600 to 799W LED light, place it at a distance of 30 to 38 inches from your plants
- If you’re using 800 to 999W LED light, place it at a distance of 32 to 42 inches from your plants
- If you’re using 1000 watts+ LED light, place it at a distance of 36 to 46 inches from your plants
Pro Tip: Do a ‘hand test’ to have a rough estimate of how far you should position your light. Put your hand where your plants are for half a minute. If your hand feels too hot for you, move the light a bit further away (even if it’s within the acceptable range).
Frequently Asked Questions
How far should LED grow lights be from cannabis plants?
1W LED bulbs should be placed at least 12’’ away from cannabis plants. 3W or 5W bulbs can be safely put at least 18’’ from the cannabis plant. High wattage (300W+) LED bulbs, meanwhile, should only be 30’ or further away from cannabis plants.
How long should grow lights be on?
Can you leave grow lights on 24 hours a day?
While you can leave grow lights on 24 hours a day, it might end up disrupting the health of your plants. Your plant use light for photosynthesis (to convert food into energy). Too much of light, with too little periods of darkness, will force them to work round the clock. This will prevent them from getting the much-needed rest which they need for energy metabolism and growth.
What plants grow under grow lights?
Multiple types of plants can be grown under grow lights. They include orchids, houseplants and even some vegetable and fruit crops. You can also start seeds with grow lights because they help ensure bulky, green seedlings. A winter harvest of salad greens is also possible with grow lights.