Hey there! Im currently using a 8×4×7 tent wth 1000w DH HPS and 1200W Led on 4 plants is it to much light or to less, sorry im not lazy just dont want to mess up the calculations if you would kindly let me know would be greatly appreciated
Hi, I have a 4′×4′ tent, which I plan on growing four plants in, so my spacing should be correct. My question to you is, in following your formula, I’m getting that I would only need 260 true watts in my tent to achieve optimal coverage. This seems a lot lower than normal. Is my math correct? Is 260 watts optimal? Please let me know if I’ve figured wrong. Just seems really low!
“am I correct to assume I need a 75 watt led for a room 2 by 2 foot with one plant in the centre?
YO THE 12×20 = 240 square feet area take 3900 watts and decide by 240 = 16.25 watts per square foot = 15600 watts for me.
I am interested in using LED’s only in a 4′ × 2′ × 5′ grow tent. What LED wattage would you recommend and do you have ones that can switch from veg growth to flowering?
“I’m starting out 4 plants tomorrow and was wondering what type of lights I would need for the vegetative stage. I am planning to put the 4 plants into a tent 4’ by 4’ with a 1000W Led but I assume that initial 1000W LED will be too strong for the seedlings.
What would you recommend?"
I have a 48×24×60 grow tent how much light & watts should I have in this space first time grower and ineed to be lead in the rite direction?
Hi, I’m new in this industry and it’s even my first grow. Very detailed articles like this have me very interested and makes me want to come back just to see if there are any other tips i can learn. This was a very detailed article and i love how you explained for each light how much we would need for space.
Great Read, even better explanation of things.
totally loving this, much appreciated. These graphs are no joke.
Hi Devin, Great information regarding lighting requirements, I appreciate it.
Yes I still don’t understand the 4 sq ft rule can you explain that to me better. For example a 4×4 grow area sq ft is 16 ×65 =1040 but using the 4 sq ft method means I would only need 4×65 =260 that doesn’t seem like enough light
How do I find how many plants I can’t fit in a room if I give them 4sq each wouldn’t that be the same math? My room is 10 × 8 so that’s 80/4 = 20. Wouldn’t that mean I can hold 29 pants?
I have a 2’ deep x 4’ wide x 6’ tall growing room/tent and i was having a hell of a time figuring out what kind of lights to get. I came across this article and boy did this end my troubles. i figured i need about 2 lights and you helped me out great yall.
“Great topic, thanks for sharing the infos.
i was able to calculate the correct amount that i will. i will use two of the S900 LED lights i am stoked!!”
Im wandering about an exhaust fan and carbon filter for odor control. Ok,after everything is hooked up,do you place the filter outside the tent? And if so does the odor stop in the carbon filter? Im new so I want to learn
If i have 4×2×6 grow tent and and i have 300 watts led full spectum.can still put some cfl?and how many watts i need more?
This information is really useful.
cool, the math is off a bit but its a bit common sense. Thanks bud!
I’ve heard that PAR is the only important thing when calculating the type of lights you need, and that watts is simply the power the light draws from the wall.
I will be growing my very first plant in the coming weeks and trying to get solid information on what grow lights to use and how much to use. This information is valuable and did what i needed it do do.
So my area is 2×4 (2×4×70 grow tent). That is 8 sq. ft.. Divided by 4, is 2 and multiply by 65 is 130. So I need 130 watts light to cover my area, great going. Look forward to growing with you!
Why is this info way more helpful than others? because you know what you are doing!! Thanks!
This is a fantastic article! Very informative. Thanks in advance for your time and reply.
“Thank you very much for the article. I’m very new at indoor growing. I’m doing right now to start my garden by seed.
I am learning as I’m going.
I will come back here for this great advice.
Thank you very much!"
Boy, was that something to read very knowledgeable. Grow ace is the best online store i came across for this kind of reads
Great question! With that grow room setup and 4x 270w HID’s, if you give your canopy 1sq.ft/plant that actually should be just enough watts for your growing area (provided you make your entire growing room floor [4×4 area] the canopy). Now, the amount of plants you can fit in a growing area does depend on the size of the pots you’re trying to use and the overall size of the plant. Start off with 4x plants in there and grow them to harvest- this will give you a gauge of how big your plants will get. From there you’ll be able to see how many more (or less) plants you can fit in that growing area
Great question, James! Whether you’re using LED grow lights or HID’s (like HPS grow lights or CMH grow lights), the wattage you need over your canopy will need to be measured in the same way. Now, the lumen output of LED’s and HID’s are different, so we can see where you might be a little confused as to measuring lumenosity vs. total wattage. However, to compensate for the intensity all you have to do is raise the light so that it does’t shine so bright on to your plants.
Exactly! The only difference is when you’re using LED grow lights you’ll need to hang them a little higher than you would HID’s. If you need a reference on how high to hang your lights check out our article here and see how far your plants need to be away from your lights source. Nonetheless, you’ll want to make sure your canopy has the correct amount of light covering it at all times, so the same rules apply in terms of wattage requirements
No problem, Aaron, it happens to all of us. It just looks like you skipped one step: applying the “4 sq.ft. per plant” rule. That means you’ll take 240 and divide it by 4, which the gives you 60sq.ft. Multiply that by 65w’s per sq.ft. and you get a total of 3900w’s needed in that room. From there it’s up to you how you’d like to go about filling the area with space. If you’re looking to go the HPS/MH route you can go with 4x 1000w HID grow light kits, or you can do the same thing with 4x LED grow lights in your grow room. With all that power you’ll need lots of room above your plants, so make sure you have lots of room above your plants to adjust lights as they grow
That’s a great idea! If you’re not in a huge collective, or if that collective has special runs of certain strains, then grow tents are going to be the way to go. No need to gut an entire room or risk growing outside in an off-season. Even better, if you want to start off with everything you need an entire grow package is definitely worth it. It keeps the guess work out of piecing it all together, and you get to try different techniques of growing and feeding your plants with gear specifically designed with harvests in mind (nothing like trying to figure out what you need and when you need it all on your own…)
“That’s certainly a great idea! With that size grow tent your canopy will pretty much be the entire tent, so with those dimensions you’ll want to fill your growing area with about 650w’s of light for both of those plants. You can shoot a little low and get a ”“http://growace.com/grow-light/600w-grow-light-kits.html”" rel=""nofollow"">600w HPS+MH grow light kit for both of those plants, or you can get closer with a <a href=""http://growace.com/grow-light/ceramic-metal-halide-light/yield-lab-professional-series-120-220v-630w-dual-bulb-cmh-complete-grow-light-kit.html"" rel=""nofollow"">630w CMH grow light and fill that canopy with a good source of light.
Make sure you have plenty of <a href=""http://growace.com/blog/air-circulation-what-you-should-know-about-the-air-in-your-grow/"">ventilation and airflow in there, too, because in a space that size with the plants and lights you’re going to have in there, things are going to get hot and sticky. To avoid problems in your garden, it’s best to make sure you have fresh air flowing throughout your garden."
“Thank you for taking the time our to read our article on calculating how many grow lights you’ll need to cover your canopy. Whether you’re trying to grow cannabis or cantaloupes, what’s important is making sure you know how many watts of light you need to fill that space, not the entire room.
You make a great point about seeking professional help when determining how many grow lights you’ll need to fill that room, and how to install them. Granted we offer a ”“https://www.youtube.com/user/GrowAce/videos”" rel=""nofollow"">complete installation guide on our YouTube channel that takes you step by step through the entire process of installing and hanging your light, we know some people would rather have another grower install them instead. In this case, make sure your trusted grower also knows how far to keep those lights away from each other and, if possible, how to install ducting from one reflector to the next for maximum cooling of your grow light and your grow room"
We’re glad we could help you out! Calculating how many watts you need in your grow tent can be tricky, especially when you’re growing cannabis. Lots of plants have wiggle room because frankly, quality isn’t a huge factor in production of, say, vegetables (most growers just want to get their produce and keep their grows moving). Cannabis can’t really take much of a hit to get a half-decent yield, so make sure that you calculate the amount of wattage you need for your weed plants to avoid overwhelming them or under-lighting them
“This is, BY FAR, the best information regarding light needs for a garden! I have seen the usual formulas repeatedly and no one has ever broken it down and explained it this thoroughly. I was using the usual way of calculating and was coming up with close to 5000 watts for a 80 sq foot space (9′×9′) which seemed ridiculous to me. Using your formula that same room needs 1316 watts….this seems much more in line.
Thanks for sharing gold!
“I use LED Lights and it’s my first time. They put out alot less wattage then most other lights. Should I still really on the watts calculation or measure lumens?
so if trying led, would you still use the same equation?
This is a wonderful and informative read. Thank you for the info!
Growing at my home I prefer to use grow tents. Just buy a complete kit and you don’t have to worry about much.
i am a first time grower i plain on buying a 4 foot by 2 foot by 5 foot grow tent would a 2 foot grow light placed in the middle be enough to grow 2 plants
Hi. How did you come up with 60 sq ft? When I mulitiply 12 × 20, I get 240 sq ft. That means you would need 15,600 watts. Am I wrong here? There is a huge difference between 15,900 and 3,900.
I have a 4×4 grow tent with (4) 270 watt high spectrum grow lights is that to much an if not how many plant should I grow?
I appreciate this information about plants and grow lights. It is good to know that calculating lights depends entirely on the section of the grow room called the canopy. I did not know that this was the place in which plants grew. Something to consider would be to seek professional help when it comes to installing a grow light system to ensure that it function properly.
“In your example above you have the lights running parallel to the short side of the grow canope area. Since the coverage area for a 1000 watt light is a 6′×6′ square, does it make any difference which way the long side of the lights are orentated?
Also just an fyi, in the example above the calulations and number of lights would be for a 6′×10′ area rather than the 12′×20′ area shown."
Hey Vinnie, great question! With T5s, the formula still applies if you’re planning on using fluorescent lights for a full grow cycle. At the minimum, you can do 45-50w per sq/ft. to achieve quality yields (depending on experience). However, you can also train your plants to grow right under the light with less wattage to get a desired yield. Hope this answers your question and let me know if you have anymore! :)
“I and a lot of people using T5 HO fluorescent.
How many grow T5 lights do my plants need?
“Well, that is one great way of looking at it. We understand these lights may be out of some growers’ budget, but you’re absolutely right: ”“http://growace.com/king-cob-480-watt-professional-series-high-coverage-cob-led-grow-light.html”" rel=""nofollow"">the King COB LED grow light more than pays for itself. If you take in to account the <a href=""http://growace.com/blog/led-grow-lights-vs-hps-grow-lights/"">advantages and disadvantage of growing with HID’s vs. LED’s, you’ll notice that you won’t need nearly half of the cooling equipment you’ll need when you run those hot HPS/MH bulbs.
Moreover, the quantity and quality of your harvests will improve, so when it comes to overall savings and quality, sometimes it’s better to save and get the more expensive lights than undercut yourself and get a light that doesn’t work as well"
Forget the initial cost. Its the amount of dope you can grow and saving a ton of money on your electrical bill in comparison to using traditional HID lamps.