Watts per square foot?

I recently changed from blurples to quantum boards, I have 240w (2x 288 boards) in a 4x2 tent giving me 30w per foot. Ive heard this is the figure to aim for!
My question is, is there an upwards limit? How much would the yield benefit from pumping it up to 50 or 60 watts per square foot?

When my boards decide to show up, I’m gonna start them at roughly 38 watts per sq ft. Under my blurples i currently pull 376 in a 2x4 and the plants love it. I’m gonna set the driver on the QBs to 300 to start and see what happens at 18” above the plants.

30w per square foot has well out performed the blurples I had before
455w of blurp vs 240w of QB..
Qb won hands down, I just want to know if there's a limit to how far I can push it

I think I was running at around 37w/psf on QB side and 45w on the cob side. Average wattages.
I have heard a couple of folks running like 20-25w too.
Perhaps @Rahz , @CobKits can give you a bit more detail or shout out those who they know tested higher w/psf or ppfd
I know @Moflow loves to photonicly rape his plants.. Don't remember to what degree though.

The info is defo on here somewhere.

im a fan of lower ppfds, and if i recall Rahz is as well.

30-35 works great for me with medium efficient rigs

CobKits said:

im a fan of lower ppfds, and if i recall Rahz is as well.

30-35 works great for me with medium efficient rigs

Click to expand...

Didn't you have a chart showing some sort of relationship between light intensity and yield and point of diminishing returns or something.
I like low ppfd too, the high GPW makes my weenis feel bigger.

Under 30watts with both my quantum boards grow and the Samsung strip builds. If you interested read my latest diary everything you could imagine needing to know will be in it.

zypheruk said:

Under 30watts with both my quantum boards grow and the Samsung strip builds. If you interested read my latest diary everything you could imagine needing to know will be in it.

Click to expand...

Less is more ime
Maybe if your VPD and everything is firing all cylinders you can take advantage of more Watts but 30W is good like @Zypher

I found that running 25 watts/SF in a 2ft by 2ft closet gave me the same yield as a 150 watt HPS. some test using only red leds shows saturation occurring at 1700ppf while others show that it occurs at 700ppf with natural sunlight. hope this helps

coreywebster said:

Didn't you have a chart showing some sort of relationship between light intensity and yield and point of diminishing returns or something.

Click to expand...

again i think that was rahz

mauricem00 said:

some test using only red leds shows saturation occurring at 1700ppf while others show that it occurs at 700ppf with natural sunlight.

Click to expand...

DLI is also a factor here

Buds.on.a.budget said:

I recently changed from blurples to quantum boards, I have 240w (2x 288 boards) in a 4x2 tent giving me 30w per foot. Ive heard this is the figure to aim for!
My question is, is there an upwards limit? How much would the yield benefit from pumping it up to 50 or 60 watts per square foot?

Click to expand...

Your question illustrates one of the challenges with lighting-how much do you need?
Using power consumed as a metric is a good start but what we really need to know is how many photons of useable light does the fixture emit. This is where efficiency changes the equation. As the lamp becomes more efficient at converting watts of electricity into photons it requires less power to achieve the same photon output as a less efficient fixture.
I find that my plants veg vigorously with 250-350 ppfd and flower at 600-900 ppfd. Ultimately, your plants will tell you what they want.

I literally have no idea what ppfd my lights are!

It's Samsung lm561c, 288 boards

At the moment it's 2 boards with a hlg 240 driver, I'm changing my set up to 4 boards with 2x hlg 240 drivers and a dimmer, so I have the ability to run the boards at a lower wattage each and still get over 30wpsf, just wondering how high I should push it, the set up will be capable of 60wpsf

OK
HLG's website gives you some basic specs that will allow you to estimate.
It says that the fixture will produce 2.43 umoles/joule. Translated, that means each watt of energy the board gets, 2.43 micro moles of photons are emitted. So, if your fixture runs 240 watts through the two boards it should produce about 580 micro moles(umole) of photons. Calculate the area you are trying to illuminate( in square meters) and divide the calculated PPF by the area and that gives you a theoretical PPFD.

CobKits said:

im a fan of lower ppfds, and if i recall Rahz is as well.

30-35 works great for me with medium efficient rigs

Click to expand...

What heights??? Thanks!

i generally run cobs at 18" above canopy

coreywebster said:

I think I was running at around 37w/psf on QB side and 45w on the cob side. Average wattages.
I have heard a couple of folks running like 20-25w too.
Perhaps @Rahz , @CobKits can give you a bit more detail or shout out those who they know tested higher w/psf or ppfd
I know @Moflow loves to photonicly rape his plants.. Don't remember to what degree though.

The info is defo on here somewhere.

Click to expand...

I started out at 750 PPFD. I've also used 1000 and 1250 PPFD since then. There are some gains to be had at higher intensities but that doesn't mean 750 PPFD is bad. 750 PPFD is easy on plants. It will provide better GPW, all other things being equal. I've found with 1250 I tend to hang them a little higher than I designed them to be. 1250 PPFD average means +1250 in the middle and -1250 at the edge, so you might end up using the dimmer or raising the lamps a bit higher than it's natural footprint. I like 1000 average at the moment. Hot spots never over 1200 and edges are 800.

umol/j * output watts = PPF which can be converted into PPFD. 1000 PPFD is generally around 20 par watts per foot, so if you know the output efficiency you can determine how many watts makes 20 par watts. 15 par watts per foot is in the 750 PPFD area.