Optimal watts per square foot?

[louie]

Pretty basic question, but what have you found to be the OPTIMAL number of watts per square foot using HPS?

 

[whodair]

depends on the height too...same light in the same square with less air above it may not work as well due to temps ... i think

 

[seebobski]

50w/per.sq.foot

 

[odium33]

a 1000w hps lamp covers a 4x4 tray well, so approximately 1000w per 16 sq ft

 

[Nor'Easter]

Most people now say 50+ as you can see here, but back in the day I did well with 20, maybe even slightly less, and those were the 4 foot Flo tubes! With the right strain and system, I heard you do not need 50, some in the old school would even say it is overkill. I would say 30-50, 40 would be fine. Most others here will suggest you have to have at least 50 and 65 is better, and some even suggest up to 100. This is just intensity insanity in my opinion, but they will say they it works for them.

 

[simon]

...and some even suggest up to 100. This is just intensity insanity in my opinion, but they will say they it works for them.

<grin> I have ~100w/ft2 in my boxes - ~6ft2 and 600HPS'. They typically produce ~2.5oz (dry/cured) GradeA bud per square foot. I run ~80w/ft2 in my main room and pull about the same, albeit from a much larger space. My veg room sees ~30w/ft2. The difference is in the shape of the room, the intent, and the needs of the plant at a given point in its life. I guess I'm trying to say that comparing raw numbers doesn't necessarily lead to a definite conclusion. FWIW, I personally wouldn't run less than ~50w/ft2 during flowering. Sure, less light intensity will still grow weed, but the quality isn't the same nor is the time better spent. YMMV

 

[Lapides]

I've just expanded my footprint to 5'x5' (i guess that's 40w/sqft) with excellent results. For years I followed the oldskool rule of thumb of 50w/sqft, but like others have said, I think that's overkill.

 

[Scrogerman]

50-75wpsf i would say is optimal, but more might be better again, makes sense, its cooling the area as you get higher wpsf that you need to watch.

 

[GanjaIsMyLife]

What about 100 wpsf if running co2?

 

[jes1243]

Elevating carbon dioxide levels can increase growth speed a great deal, perhaps even double it. It seems that the plant evolved in primordial times when natural CO2 levels were many times what they are today. The plant uses CO2 for photosynthesis to create sugars it uses to build plant tissues. Elevating the CO2 level will increase the plants ability to manufacture these sugars and plant growth rate is enhanced considerably.

more light the better just as long as it is not burning the plant but light spec is something you might want to look at too (colors in the light)

 

[CanIgetsum]

50 watts per sq. ft sounds about rite.

 

[250wscrogger]

I learned a couple years ago that giving less watts per sq ft but more area per light can make it much easier to hit the yields you're looking for.
People say 3x3 per 600w but I do 4x4 per 600w and hit 1lb per easily...I NEVER hit 1lb per 600w till I expanded the footprint to 4x4. Most people going 4x4 per 1000w will never hit 2lbs per light...but a lot of people going 5x5 hit 1.75+ on a regular basis.
It's a lot easier to grow 16 2oz plants in 25 sqft rather than trying to pack them into 16sqft.
I try to keep it around 40w per sqft now.

 

[joe fresh]

i have experience in using up to 90w/sqr ft, and must say its a waste of light, using 50 w/sqr ft i get the same yield, (maybe more due to less stress, a/c blowing cold air non-stop leaving the rest of the room under the lights hot with a steady stream of cold air, pots dry up quicker....ect) but like said above with higher cielings it might make a huge diff.

but in general i would say anywhere from 40-50 watts per square foot is optimal, anything more will cost more(electricity) but will not yield more, and that is what i mean by OPTIMAL


ps. im also using co2 @ 1700ppm

 

[louie]

Thanks for the info guys! Yeah I've always heard and used 50 watts/ ft^2, but might play around with somewhere in the 40s and see if it makes any difference.

 

[simon]

Wpsf assumes that light is the limiting factor. Often, space is the limiting factor, not light. Then there are ventilation concerns, the config of the garden, growing methodology and a myriad of other factors that modify the equation. There's no cut and dry rule that covers it all. Just as some folks have trouble maintaining 50w/ft2 without encountering heat issues , there are 100w/ft2 boxes run 1-2F above ambient. I mention this to make a point. There are too many variables to expect a valid, all-applicable solution.

Simon

 

[Nor'Easter]

I learned a couple years ago that giving less watts per sq ft but more area per light can make it much easier to hit the yields you're looking for.
People say 3x3 per 600w but I do 4x4 per 600w and hit 1lb per easily...I NEVER hit 1lb per 600w till I expanded the footprint to 4x4. Most people going 4x4 per 1000w will never hit 2lbs per light...but a lot of people going 5x5 hit 1.75+ on a regular basis.
It's a lot easier to grow 16 2oz plants in 25 sqft rather than trying to pack them into 16sqft.
I try to keep it around 40w per sqft now.

exactly! It seems like common sense that a bigger footprint results in the room being easier to cool, I can't imagine how someone could have over 50 and not have a hell of a time cooling the room. I have seen results posted (here I beleive) where the intensity was down to 30 or even 20-something PSF, and some commercial warehouse growers all the way down to like 15 or less. I would hesitate to do less than 20 and would probably do 40-50, but I know I saw a post somewhere where Tom Hill said some have had great results growing Deep Chunk in an 8 x 8 space with 1000 W! In fact, I think he said it does BETTER with lower intensities like that!

But simon makes great points, different things work for different people in different situations. Some strains require a high intensity to produce great buds. Many different ways to get great results. peace