This is one of the questions that frustrated me most when I started growing with LEDs
There’s so much technical jargon mixed in with marketing falsehoods that choosing the right LED grow light is confusing.
So, what Size LED Grow Light Do I Need?
For optimum yield, A good rule of thumb is to choose an LED grow light that outputs at least 50w per square foot of grow space. Make sure that the light can draw 50w from the wall (not the combined capacity of the LED’s) Example: a 2ft long x 3ft wide grow space would require a 300w LED grow light
This is a good starting point, but there’s a bit more to it.
Read on to find out exactly how to find the right size of grow light for your setup.
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What Size LED Grow Light Do I Need?
The most important bit of equipment in your grow room is your light.
Why? Light is your plant’s food, you need to feed your plants high-quality food for them to produce high-quality yields.
LED lights for weed are now considered the best lighting option by most growers due to their energy efficiency, durability, and full spectrum.
However, with all the options and technical jargon, finding the right light for your project can feel a little overwhelming.
To work out what size of LED grow light you need, you first need to calculate the exact size of your grow space.
The Size Of Your Grow Space
When growing cannabis, a good rule of thumb is to use a minimum of 50 watts of light per square foot of grow space.
We want to flood our plants with light ( food ) so that they have lots of energy to produce big potent buds.
Therefore, we need to calculate the square footage ( length x width ) of our grow space.
We’ll then multiply this number by 50w to give us the rough wattage of light we require.
EXAMPLE: I have a grow space that is 2ft long and 3ft wide. This gives me a square foot grow space of 6 ( 2ft x 3ft ). I would then multiply this number by 50w, which gives me 300w. Therefore, in this example, I would require an LED grow light that was at least 300w.
How Many Plants Can I Grow?
In general, each cannabis plant you grow requires at least 1sq ft of space.
After germination, I like to place one plant in a large 5-gallon fabric container, which has a diameter of roughly 1 sq foot.
My plant will stay in this pot until it flowers.
This allows the plant to grow big and strong without other plants or tent walls obstructing its progress. I also don’t like transferring plants too often, as it puts a lot of stress on the plant.
So this as a guideline, I would be able to grow between 1-6 plants in my example above.
Make Sure Your Canopy Is Covered
Now, it’s also important to understand that most LED grow lights will usually only be able to cover around 1- 6 plants.
If you want to grow any more plans than this, you would need to purchase multiple lights to hang side by side ( called daisy-chaining ) to cover the canopy and ensure each plant is getting equal light.
The table below shows how the number of watts you require increases with the size of your grow space. I’ve also included how many plants each size of grow light will be adequate for.
Note: 1 sq ft grow space = 50 watts LED grow light
| Grow Space Size | Minimum Number of Watts Required | Number of Plants You Can Grow |
|---|---|---|
| 2 sq ft (2×1) | 100w | 1-2 plants |
| 4 sq ft (2×2) | 200w | 1-3 plants |
| 6 sq ft (2×3) | 300w | 1-6 plants |
| 9 sq ft (3×3) | 450w | 1-9 plants* |
| 12 sq ft (3×4) | 600w | 1-12 plants* |
| 16 sq ft (4×4) | 800w | 1-16 plants* |
| 20 sq ft (4×5) | 1000w | 1-20 plants* |
* The size of the grow space in these situations will require you to purchase multiple lights to hang side by side to ensure the entire canopy is receiving light.
Note: The values above are for flowering. During the vegetation stage, you will require around half the power ( 25w ) the best quality LED grow lights come with “Veg and Bloom switch” that optimize the intensity of the light for the vegetation and flowering stages.
Understanding PAR Output
You’ve probably heard about PAR. In simple terms, It’s the part of the light spectrum that your plants use for photosynthesis.
So It’s a pretty big deal.
The higher the PAR output of your light, the more edible light your plants receive.
Take a look at the table below for the optimal ranges of PAR for each stage of your plans life:
| Stage | Optimal PAR Output |
|---|---|
| Seedling | 200-400 (μmol/m2/s) |
| Veg | 400-600 (μmol/m2/s) |
| Flowering | 600-900 (μmol/m2/s) |
Ideally, you want to pick a grow light that outputs PAR in the ranges above.
This pretty much rules out any LED grow light below 300w, as they simply don’t have enough power to generate the required levels of PAR.
That said, keep in mind that these are optimal levels of PAR. Using a grow light that has less PAR output than these ranges will not be a disaster, you just won’t max out the potential of your plant.
So, Which LED Grow Light Should You Pick?
If you’re still unsure which LED grow light to go for, then I’ve written a detailed guide to the best LED grow lights that you might find helpful.
Alternatively, the three LED grow lights below are perfect for a small grow set up of between 1 – 4 plants inside a 1 sq ft – 4 sq ft grow space.
Final Thoughts
Hopefully, this article has been able to shed some light ( pun intended ) on how to pick the correct size to grow light for your project.
As long as you know the size of your grow space and how many watts per square meter you need, choosing an LED grow light is pretty simple.
Good luck with your grow!
Originally posted 2018-01-24 01:06:33.
James Alexander
Great information, just what I was searching for, Thanks for sharing your knowledge.
Hello I’m doing a greenhouse and each bed is 114 sq ft with two beds. Each bed will have 40 plants. What would your suggestion be for lighting .
10×10 grow tent with 20 plants what LEDs do I need
I am going to have a 3×3 grow tent with 4 to 6 plants what LED light would you recomend me getting? And how far from the plant should i keep the light? Im wanting to have shorter plants.
I have a plant light thats 8 watts will that be enough for one plant im growing it outside right now and plan on bringing it in before the time changes. Tips and advice would be awesome thanks
Hi. Have 2 75 watt led lights. Just got a 600 watt light from Amazon with veg/flowering switch. Also has cooling fans. Think I made a good choice? I’m just getting started. Grow just for me.
am starting out to what light should i get and how far from the plant
I have 2 greenhouses with 2700 square ft of space in each.How many 1200 watt led lights do I need in each one?
i have a 600w and a 1000w led side by side in a 2×3 space, too much?
I’d be more concerned about uneven light distribution to your canopy. What are the actual watts output by each light? Also, how many plants are you looking to grow?
No, I have one 1200W LED and two 600W LED lights…I hang one or all three or hang one and put one on each side standing up length ways…you can never have too much LED light…too liuttle for sure, but not too much. Get yourself some Emergency Blankets…cheap and reflective…unless you have a tent. I just made a spot beside my furnace in the cdellar…perfect. Good luck.
When talking about watts, are you talking about the wattage being drawn at the wall or the LED’s themselves?
that’s a great question. go for the led itself. I like cobs. cree cobs with a meanwell driver or a great driver and Samsung chips cannot be beat. peace and love
Hi I’ve just got a 100x100x180 Marshydro upgraded tent and I’m putting 4 plants in 15 litre Autopots in the tent. Would a 3000w Bestva led light be to big and would it damage my plants ?
I have a 600w cob light for a single plant in a 16×16 inches grow tent, too much?
its your electric bill. a great 600w cob can easily cover a 4.5x 4.5 foot in flower. I like nielo led cob boxes quite a bit. a good 1,100 watt cob with double chips and about 65 of those chips with a dimmer is pulling far more than you need off a wall but still saving you money. then you could use that light in the future at 90% luminosity on 3 big plants. I love cob lights. good choice. peace
I have a grow room — 8×10 with 3 plants and 2 LED lights that say their 1500 watts each is that enough light the room is 8’ tall and the plants end up touching each other
Was wondering of a 27watt full spectrum led growlight grow an amphetimine auto in a small space?
Would it be best to have a couple of 1,000 watt fittings for maybe 4 plants to get the coverage / penetration evenly distributed? Or not really?
Thanks
Hi, James, great article. However, I cannot use the information just yet…. I need to know are you talking about watts advertised (equivalent to HPS), or actual power draw from the wall. Eg. I am growing 8 small auto flowers in a 4×3 space. Plants are small, using about 1sq ft each. I am using a Bestva 800w (dual chip 10w) LED, with actual power draw from the wall of 150w. In your calculation I need abut 600w minimum. But are you referring to advertised wattage or actual power draw? Thanks!
How about a 1200w Roleadro in a 48”x48”x80” tent? I’m beginning to wonder if I have too much light, if that’s possible?
I have a 4’x4’x80” tent. I’m using a 1500w led, because I had it before I decided to grow, growing 2 plants. Is this too much? I don’t want it to fry the plants when they get too tall. I’m a beginner so I topped at about 12” inches in height. I’m worried this light is to much and wondered if I should clone them out completely or figure out how to keep them from getting burnt if they get too tall!? PLEASE HELP! Seeds are expensive and I only have to plants to work with. Thanks in advance!
4 x 4 x 80 grow tent. Will a 600w work for three plants I’m bringing in from outside.
Hi guys growing with a 1000w led, am at flowering stage, 6 weeks in, and no flower show as such. Lights are at 12 inches above the scrog canopy, too close maybe? No leaf burn no problems to see? Feminised stock no flower, stumped!
Did you switch your light cycles? Did you change to 12 hours on 12 off?
I am looking for a light for a 60 by 60 Indoor and greenhouse
People asking what wattage they need for so many plants & space.. why don’t you all just read the article… it explains it all
Are 2 , 600 watt lights good for a 5\4 grow tent? 1st time I’m only doing 6 plants. I got ventilation. Fabric pots, foxfarm. Is that to much watts?
Can i use both veg & flower switches at the same time for an auto-flower plant 5 weeks old ?
Hi ,my growing area is 3 meter x 4 meter. How many plants and lights i need
Thanx Bennybeervel
When talking watts and LED lights, are you talking about what the manufacturer claims the light’s wattage is, or are you talking about the wattage the light draws from the wall?
Is 2 10 watt full spectrum led lights that are adjustable, and 3 34 watt t8s, and a few 35 watt flourecent spiral bulbs enough to grow 2 plants through full grow, with little to no experience or expectations? More of an experiment, I have one monkey glue and one wedding cake, as long as they are females, of course. Just wondering. I sprouted them a week ago and they are doing great, what type of yeild should I expect if any, and quality? I will be supplying nutrients as needed, so my main concern is lighting
I forgot to mention, I plan on doing any training I can to keep them short and the canopy as flat as I can, while trimming undergrowth
Hi
What will happen if I’m using v99grow led light 1000 w on a really small tent 0.4×0.4×1.2m ?
Thanks
I have a 2′ X 4′ X ‘6 grow tent. I have a 1500 watt LED grow light.Is this too much light for 3 plants? I noticed I have my second set of nodes growing and my plant is barely 2 in tall. If this is too much light, would a 600 watt or 800 watt light work better?
Hi , what’s the best temperature when you flower under 1000 watt spider and using 800/900 ppm
Please answer me?