How much light do you really need?

How much light do you really need to grow a plant wattage wise? I talked to a guy and he was saying that you need 400 watts for a specific Tent and maybe more would be better. I said if can grow a plant with 65 watts why waste the money on the additional wattage? He seemed unable to provide me with an answer. He said there is a lot of variables. Once I told him I knew for a fact 400 Watts was not entirely necessary the guy shut up and didn’t want to discuss minimums with me. I had talked to a different guy and he claimed he was growing 4 plants with 110 watts and he having no problems. I wondered what is really necessary?


Lots of variables there, number one what type of light as there are many. Many people grow one or two plants on a 250 watt HPS. Flowering is where u need more light. I veg mine on a 100 watt led


You won’t get much off 65 total watts. The amount of light is King. So you can’t cheap out on. Especially if you use marijuana to say treat pain like I do and need more than say 12 grams per month.

Total watts is also determined by how many plants you want to grow and the size of the tent.

I will use this as an example.

This was achieved with 2 HLG 260xl Rspec which is 550 watts from the wall or close to it. You will not achieve a plant like this with 65 watts.

Here she is cut in 1/2 so it wouldn’t be on the floor and I can reach over 7’ with my gorilla arms. This plant was 2 feet out of the tent. She was 8’ tall by 8’ wide. It took a 4x4x80” tent by herself. Her main cola was the size of a volleyball.

If you don’t believe me, let me bring in the Light Guru who will give you the information you are seeking. Here you go @dbrn32. Your expertise is needed.

With it being X-mas tomorrow just be patient as people have families and celebrating. When @dbrn32 talks about lights, he knows what he is talking about.


Growing a plant indoors is not about wattage It is about spectrum. The thing about wattage is the more you have the further down you are going to push that same spectrum.
So a low wattage light of 100 actual watts with a certain spectrum will push its full spectrum let’s say 6 inches through the canopy. Now take that same spectrum of light and give it 200 actual watts and it will push that full spectrum further through the canopy let’s say 10 inches. Giving the plant more vigor to produce Its fruit in the lower part of the plant.
If you are growing a 6 inch tall by 10 inch around plant 100 watts will probably do it. But not many are doing that. More watts equal bigger more vigorous plants (bigger tighter buds).
Not real numbers so does not really answer you question. Eh no big just felt like yakking.


I use a 300 watt light and i have used 150watt lights


The difference between 1-2oz and 8-28oz but yeah you can grow weed with a house lamp if ya want to.
I prefer to grow a few grand worth of meds at a time rather then a few hundred dollars :man_shrugging:
But that’s just me :grin:


It won’t be a waste. The waste would be not allowing the plant to grow to it’s full potential. 65 watts is enough to grow a plant. It is not enough to grow a quality plant with a substantial yield…


If you are happy with light airy buds that are of low quality, then you are entirely correct. Most of us want to and do grow dense buds of very high quality. To grow high quality product you need high quality light and a lot of it. Depending upon the quality of light, you will need from 35 - 50 watts per square foot of growing area.

A more accurate measure of the light required is to look at ppfd (light intensity) in the PAR spectrum. For most of Veg and Flower I run a ppfd of 700+. Less during seedling stage and a little less late in flower.

If it were not required to get the yield and quality that I want, I would not waste money on high quality, high intensity lights. That is not to mention the cost of running those lights.

Good luck finding the information that you seek.
Other folks that may want to weigh in here are:
@dbrn32 @Covertgrower @AfgVet @MattyBear @Joshmcginnis28 @Dman1969 (Plus many others)

Note: Personally, I tend to run very high quality lights at about 50 watts per square foot. Many consider that to be over kill.


I’m a Mh/Hps kinda guy at the moment. And I’m with @merlin44 . If you want a quality plant grown to its full potential you want a quality light. My light is a little more expensive on the light bill and produces a bit more heat. But my 1000 watt light covers 5 x 5 footprint. Costs 125 bucks. :sunglasses::v:


I should also add that my first grow was nearly four years ago with purple LED’s that were typical on Amazon at the time. I thought that I was killing it with light at 25 watts per square foot. I grew six plants and got about 27 ounces of larfy buds that were of modest to poor quality.

That is when I realized that I had to improve the lighting situation. I now get about one pound of really good quality buds per plant when I grow six plants in my 8 X 8 foot (really only 6 X 8 plant area) main room. The advice of the really excellent growers on this forum got me pointed in the right direction.


Well said @merlin44 Most important equipment indoor grow quality LIGHTS equal quality buds. Happy holidays my friend !


Thank you for your support @kellydans
Happy holidays to you and your family.

To you too @Oldguy, I saw you “liking” about there.


@merlin44 Thank you Mr Merlin. :grin:
Best of the season to you and ur Mrs.
Just doin a quick scan before I wash some roots off.:grin: Gnats on a clone.
Tryin a wash and replant in fresh soil. :crossed_fingers:


I will also add that wattage per square foot was a metric we used years ago, but we are becoming more sophisticated and knowledgeable (in no small part to @dbrn32). As @merlin44 pointed out; there are different methods for measuring the correct light intensity and spectrum. Modern high-end LED’s blow absolutely everything else out of the water in every category except price. That said, the lights will pay for themselves in no time.

I went diy and the first month I ran my lights my electric bill went down $60. I normally yield 32 to 34 oz of primo flower with 3 plants.

Everything starts with the light.

Merry Christmas all!


Does the 50 watts / ft2 guidance need to be updated or modified for LED? HID wastes so much more of the wattage to heat, I would think the number for LED was significantly less.

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If good quality LEDs u can get away with around 35w psf cheaper brands is when u need a bit more basically falls on the type of chip used so it seems. The driver will drive it but with a shit chip u’ll get a shit spectrum. Like my enfun boards I’d say r more of the 50w psf where my hlgs can get away with 30 to 40 super easy.

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No minimum amount of watts that I know of. Should be looking at your photosynthetic photon flux density. Since some lights produce more photons per watt, it’s extremely difficult measure light by watts in terms of what plants need.

Making a plant grow with low powered light is plenty reasonable. But getting it to produce enough flower to justify your time and efforts is another story.


I think you said all there is to say @merlin44. Poor quality lights will get you a poor quality harvest


So you think 425 watts is good in 3x3 or you think 300 is acceptable to get the most use out of the space?

That maybe a little more than you need for a 3x3. If you have that much, the lights pay for themselves with 1 successful crop.

I will say what I did. I drove to Denver aka over 1000 miles away to get bud. I didn’t want to risk getting caught in a Sting by the Police. I made 3 trips for over 6000 miles total. First time I rented a car with 50+ mpg. Second trip me and mom went in her Toyota. Good mpg. Last was on my Harley. I spent a lot of cash. Each trip I spent over $1200 on marijuana. So over $3600. :flushed::flushed::flushed:

I then got into growing home. My sister knew I was planning to buy 5 acres in Souther Colorado. So she said yes to growing.

I got a Viparspectra PAR600 light. Then joined here and got a second one. I spent $500 between the two.

I was able to get 8oz off one plant under these lights. I said screw this and jumped on the HLG train as many growers said they was awesome. Of course @dbrn32 said which ones to get for my 4x4. I listened to him even thought I was only on the forum 1 month. Glad I listened.

Now my total watts off the wall was about the same between the Vipar’s and HLG 260xl Rspec. With the HLG’s my first crop yielded over 2 lbs dried, cured and no stems.

Huge difference. Some of my plants under the Vipars was larf and others with solid buds as if they was under HLG lights. The strain made the difference.

Under HLG lights I don’t get airy buds. As you can see I wasted well past $5000 between my three trips and the Vipars. I could have one hell of a setup if I would have joined here long before I bought what I did.

I hope this helps you to decide on better choices than many of us made mistakes on crappy lights.

I need serious weight and quality due to the massive damage to my body from Serving. Depends I may smoke 1oz a month and the pain gets bad and I may smoke 3oz in a month. I have to have quality and weight.