Lights required per sq foot


My apologies for the delay but I guess I replied too much on my first day as a newbie to the form :wink:

Ha ha.

Great point and one I was going to mention on the thread developed but you beat me to it :+1:t2:

The numbers didn’t make sense.

I guess that leaves me asking Is 65W per square feet the “optimal light required” ?
Is this all the plant requires to achieve its maximum potential, producing just as much as with 260W per 4x4 as it would with 600W covering the same 4x4 space making the extra 340 W of overkill. :thinking:

Appreciate all the feedback.



Looks good and donapprexiate the time and efforts.

Again, this was not anhuestion to try to conserve energy and save money on lights … we use what gives the max yields :wink:

This was just a question to about yield, and thinking maybe I was missing something.

Great post and thanks for this handy app :wink:



In my opinion, it’s s lot better to Target your par levels than how much power you’re consuming. That’s just because of the differences in lighting efficiencies. Using something like cmh or some good leds you can put a little more par into your space for less power.

Without getting to technical, horticulture lighting efficiencies are generally measured as umol per joule. In simple terms that’s photosynthetic active radiation per watt per second. An eye hortilux super enhanced 1000 watt hps tests out around 1.2 umols per joule. A gavita double ended 1000 watt at max tests out around 1.9 umol per joule. So at 65 watts per square foot the de gavita will have almost 35% more light than the hortilux fixture. Or you can run about 35% less power to achieve similar light levels. However you want to look at it.

If you’re going with standard single ended hps tech, 65 watts per square feet sounds like reasonable number. If you’re using good hoods and reflective surfaces around your grow you could maybe even get by with a little less.


If that’s the case, I would probably use a bunch of DE 1000’s. The spectrum they put off and like Dbrn32 was saying the light they put out is really good. To be honest, I would figure out what brand of light you’re going with. Then work from that, as that will make everything so much easier in figuring out how many lights and plants you can do with them.


Hello, growing my first plant and have a general light question… What will end up happening to the plant if you don’t have “enough light” for it during flower? Will it just not produce as much quantity? I am just growing for personal use so I have no need for lbs of weed, and I am also having fun just going through the process! :slight_smile:.

1 plant, hydro system, 45w LED (like what you can find at big box home improvement stores).



You generally want 25-50 watts per square foot, but if you really want to know about lighting, you need or lighting guru, @dbrn32.


Thanks for the reply… I am hoping that @dbrn32 chimes in!


I’m sure he will, he might be at work right now, so be patient.


Here, but out of likes sorry. You’re absolutely correct. As long as you have the right kind of light, being under powered usually just ends up creating smaller relatively airy buds. You can literally grow weed from seed to harvest under a couple of cfl’s.

The problem is usually in people that buy a relatively large tent and then an led fixture with s number like 1200 deceptively attaches to it and think they’re gonna grow s pound or two of weed in it. I usually have to be the a-hole that points out it’s not exactly feasible to grow a pound of weed out of a couple hundred dollar setup.

With a few reasonable measures though you can absolutely grow a little bit of weed on a low cost grow though. For a relatively new grower with blurple or an a19 bulb light, it seems the grows that go well usually end up around .5 grams per actual watt of light consumption. There’s lots of variables though, so consider that a rough estimate.

A couple of things that will probably help you out, is definitely keep an eye on your light heights early. The last thing you want is s tall stretched plant. Also, look into some training methods to keep your plant short. Something like a scrog is really good for a low powered light. Or a little bit of early bending will slow the top down a little bit and redirect energy to your lowers giving you a multiple top look. In general just keep your plant from getting too big and swallowing your light and you can be plenty successful.

There’s not a lot of micro growers here to point you towards. But be careful trying to implement some of the things people growing big are going. @MattyBear @raustin @Dieselgrower all come to mind growing pretty damn well in smallish spaces. You can probably follow along their grows and pick up some more advanced defoliation techniques that may help too.


Thanks for the kind words. I definitely agree that the blurple lights have their place in growing. They can be misleading in their “true” power and I believe most of us have fallen down that trap, in some sort of rite-of-passage. I’ve been able to push to a little over .50 gpw with mine. As db said training the plant will go along way to increase yeaids. Yes these plants can be pretty flexable and forgiving, but as with everything. The closer to optimal environment you are the better the plant is going to do. I’ve been growing just a little under 2 years and I still have a lot to learn and it seems like there’s always something new out there. I have a couple of small tents I use for now. If you need anything or have a question don’t hesitate to ask. I’ll try an help as much as I can.


Thanks all for the info! I definitely kept the plant small (less than two feet tall). I topped it early, and fimmed the 4 main branches shortly thereafter… Will have to upload some pictures when I have a chance. I have just been nervous that the light will not even “finish” it properly. I am 4 weeks into flower and I think it’s looking good, but I’ve never done it before, so not positive. Would the low light also cause the flowering cycle to be drawn out for longer?

Thanks again!


Not necessarily, that will vary regardless.


You could never come off as an a-hole, @dbrn32. We value your opinion too much.


Haha thanks!


@dbrn32… Would you suggest maybe adding this light to my system at this point?

Or is there something better to add for around $150 that you would suggest?

I am in week 4 of flowering… Or is it too late to add lighting now?


What size is your tent?


It is in a closet that is roughly 3’x3’x6’


It’s better than what you have for sure. If you’re willing to spend that, I would just save a little longer and get something of a little higher efficiency.


What would you suggest if I can get more money to throw at it? I would only want to grow 1-2 plants at a time to start, but maybe expand in the future! Also, would it be worth it to throw some individual lights at it now just to increase the yields just a little bit?



The HLG 260w kit is great for a 3x3. I’m sure @dbrn32 would recommend it. I am running it as well as a few other members. It’s the hot grow light out atm. If you have a little knowledge in handy work you can easily save some money but DIY a kit yourself. Or a COB (chip on board) setup is good also. That kit is 305$-330$(depending on boards used.) but is well worth it. Like I said if you can do a bit of wiring and such then you would be able to buy a few things seperate and save some money as well.