Switching from 55W/ft^2 of 4K LM561C to 30W/ft^2 of 4K LM561C

Quick question,

My light is a home made 2x4 with 2ft single row strips 1.5" apart, total of 16, driving them at about 27.5 watts a piece. Each half is powered by a meanwell 240w driver.

Contemplating splitting my grow light into two, taking out every other row, and adding one additional row to each so they'll each have 9 strips, maxing out the driver, and balancing out the lighting. They would then have a 4" gap between each strip and would be at 30W/ft^2

Then I'd have two 2x4 grow setups for almost no extra costs, not in new lighting nor in more electricity.

My question to you guys who have experience with grows with these lights, how big of an impact am I going to see (loss) in yield and quality? My grow right now is at 1.5 weeks of flower, 8 weeks of veg, 6 plants, 5 strains, and they're doing pretty well despite all of my first grow blunders. The canopy is filled and they are all extremely dense. I'd be sad to lose that on my next grow. But I'd love to have a perpetual grow, and I've also read some people say that anything over 35w/ft^2 is overkill with the LM561C, not sure if they're just assuming that or have actually done some side by side tests.

Thanks guys,

sunsp0ts

sunsp0ts said:

But I'd love to have a perpetual grow, and I've also read some people say that anything over 35w/ft^2 is overkill with the LM561C, not sure if they're just assuming that or have actually done some side by side tests.

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You would be amazed at some of the testing RIU members have done! You should do a test yourself, by gradually reducing the light. Suddenly changing from 55w to 30 seems a bit drastic.

Wow, 55w/ft is a LOT of light, especially for a first grow! Are you running C02? From what I read here, I think you might get better results at 30w than 55w.

Some run up to 50w, but the consensus is 30-35w with good stuff like the LM561C.
@Randomblame and other respected members feel that extreme light levels tend to cause problems, especially for the less experienced. The plants are less forgiving, so nutrients, temperatures, humidity, etc. really need to be on point. It's all about keeping everything in balance.

Related threads..
https://www.rollitup.org/t/how-many-umols-for-fllowering.972399/page-2
https://www.rollitup.org/t/slow-yellowish-growth-under-vero-29-3000k-3500k.962065/page-2
https://www.rollitup.org/t/height-power-to-canopy-for-samsung-leds.975149/page-2
https://www.rollitup.org/t/led-light-intensity.960838/page-9

If youre set on running 2 tents (which can be done on nicely on a flip flop ) and doing 4x2 with decent light levels:
Why dont you build 2 frames, big enough to do the full 4x2 but you only light a 3x2 each and dont fill the 2 tents completely. That way you would be doing 40w per square foot assuming 240 drivers which is defo enough. And if you see you wanna do the full 4x2 buy some more strips to fill in the last foot and then you run 30w/ square foot? This is of course assuming youre running CV drivers so you could add as many strips as you want.

Whats the hanging height of your fixture right now? If its a foot or so you can achive the same light levels at a lower height but using a few more strips to get the spread right, using less wattage. Ymmv

sunsp0ts said:

Quick question,

My light is a home made 2x4 with 2ft single row strips 1.5" apart, total of 16, driving them at about 27.5 watts a piece. Each half is powered by a meanwell 240w driver.

Contemplating splitting my grow light into two, taking out every other row, and adding one additional row to each so they'll each have 9 strips, maxing out the driver, and balancing out the lighting. They would then have a 4" gap between each strip and would be at 30W/ft^2

Then I'd have two 2x4 grow setups for almost no extra costs, not in new lighting nor in more electricity.

My question to you guys who have experience with grows with these lights, how big of an impact am I going to see (loss) in yield and quality? My grow right now is at 1.5 weeks of flower, 8 weeks of veg, 6 plants, 5 strains, and they're doing pretty well despite all of my first grow blunders. The canopy is filled and they are all extremely dense. I'd be sad to lose that on my next grow. But I'd love to have a perpetual grow, and I've also read some people say that anything over 35w/ft^2 is overkill with the LM561C, not sure if they're just assuming that or have actually done some side by side tests.

Thanks guys,

sunsp0ts

Click to expand...

I would guess you would increase yield by like 25-50% overall you will have higher gpw but lower g/sqft

sunsp0ts said:

Quick question,

My light is a home made 2x4 with 2ft single row strips 1.5" apart, total of 16, driving them at about 27.5 watts a piece. Each half is powered by a meanwell 240w driver.

Contemplating splitting my grow light into two, taking out every other row, and adding one additional row to each so they'll each have 9 strips, maxing out the driver, and balancing out the lighting. They would then have a 4" gap between each strip and would be at 30W/ft^2

Then I'd have two 2x4 grow setups for almost no extra costs, not in new lighting nor in more electricity.

My question to you guys who have experience with grows with these lights, how big of an impact am I going to see (loss) in yield and quality? My grow right now is at 1.5 weeks of flower, 8 weeks of veg, 6 plants, 5 strains, and they're doing pretty well despite all of my first grow blunders. The canopy is filled and they are all extremely dense. I'd be sad to lose that on my next grow. But I'd love to have a perpetual grow, and I've also read some people say that anything over 35w/ft^2 is overkill with the LM561C, not sure if they're just assuming that or have actually done some side by side tests.

Thanks guys,

sunsp0ts

Click to expand...

Nope, more like 35w is not overkill it depends on the situation. Without additional CO² the highest intensity is below 1000μMol/s/m² and from 30-35w/sft you can expect to get 800-900. With CO²(1000-1500ppm) the plants can handle even more light and up to 1200μMol/s/m² can be used. To reach that level of intensity you'll need ~45w/sft.

But the hanging height is important. With 3" gaps between strips you get optimal uniformity already with only 3-6" hanging height. Even with only 30-35w/sft you'd probably measure around 1000μMol/s at this level.
I have 20 low driven F-strips, 8 low driven COB's and a few far-reds, only 335w at the wall above 10sft, 33,5w/sft and I get my desired intensity with 12-14" (900μMol/s). Good uniformity (~80%) already from 6-8" but I have added a UVB bulb and need the 12-14" for good UVB coverage.
I would recommend to invest in a cheap e3ay lux meter(12$) and use conversion factor 69(for 3000°k) to convert lux readings to μMol/s/m². Below are the LM561c numbers for all available F-strip CCT's...
It helps a lot to figure out the optimal hanging height and when you have the found best distance you should only use the dimmer to regulate the intensity level.
Good uniformity with less distance is the main benefit when using strips but in the same time it's also their biggest downside. They literally kiss the tent walls and with more distance more light gets lost on the walls.

Thanks for posting RB, I had lost the chart.

It's my first grow, I am supplementing CO2. My plants are doing extremely well, or so I like to think (perhaps they're not, I have no basis for comparison besides pictures I see of other grows and my girls grew so dense during veg that I could not see their primary stem from any angle without heavily spreading the plant apart) I keep my light about 6-14 inches away. The only reason there is such a difference is because I'm doing experiments from one plant to the next, topping some, others not, training every plant in a different way, etc. I'm a scientist/engineer by trade and instinctively, so I can't help but run experiments, they aren't the best control conditions or sample sizes but they are good enough to help me decide on a strategy for future runs. There is no bleaching, no burning, my temps and humidity are all controlled to an excessive degree. I used soil for my first grow sadly, I was worried I'd have problems if I went all out, I'll never use soil again on future runs.

@1212ham, I don't know how less light could be better unless I was burning them somehow, and heat is not an issue. I have two high power fans, one for intake one for out, and they clear the humidity and heat within a few moments. I monitor the heat on my canopy with a FLIR infrared thermal imaging camera and I have them set to about 78 right now during flowering with CO2 supplementation.

@RocketSoul, I like your way of thinking. I might do that, actually.

@Randomblame, light uniformity is the primary reason I went with strips. I go all 4K, btw, not a fan of 3K, although I do realize it's the fan favorite. So your figures may differ based on that, your ratio was for 3K, Do you know what they are for 4K? EDIT: It's in the graph you put up, oops! Didn't realize that info was in there. Thanks again. Going to order a lux meter. Do you have a link for one you recommend?

Thanks again for all of your help and insight everyone!

sunsp0ts said:

It's my first grow, I am supplementing CO2. My plants are doing extremely well, or so I like to think (perhaps they're not, I have no basis for comparison besides pictures I see of other grows and my girls grew so dense during veg that I could not see their primary stem from any angle without heavily spreading the plant apart) I keep my light about 6-14 inches away. The only reason there is such a difference is because I'm doing experiments from one plant to the next, topping some, others not, training every plant in a different way, etc. I'm a scientist/engineer by trade and instinctively, so I can't help but run experiments, they aren't the best control conditions or sample sizes but they are good enough to help me decide on a strategy for future runs. There is no bleaching, no burning, my temps and humidity are all controlled to an excessive degree. I used soil for my first grow sadly, I was worried I'd have problems if I went all out, I'll never use soil again on future runs.

@1212ham, I don't know how less light could be better unless I was burning them somehow, and heat is not an issue. I have two high power fans, one for intake one for out, and they clear the humidity and heat within a few moments. I monitor the heat on my canopy with a FLIR infrared thermal imaging camera and I have them set to about 78 right now during flowering with CO2 supplementation.

@RocketSoul, I like your way of thinking. I might do that, actually.

@Randomblame, light uniformity is the primary reason I went with strips. I go all 4K, btw, not a fan of 3K, although I do realize it's the fan favorite. So your figures may differ based on that, your ratio was for 3K, Do you know what they are for 4K? EDIT: It's in the graph you put up, oops! Didn't realize that info was in there. Thanks again. Going to order a lux meter. Do you have a link for one you recommend?

Thanks again for all of your help and insight everyone!

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2 things I would like to mention.
First, with LED we need a higher ambient temps to get the desired leaf temps for optimal photosyntesis. Compared to HPS LED has almost no far red and absolute no infra red but HPS have a huge spike in the 800-850nm range which means ~25% of the light is heat radiation. For this reason we set the temps to 25°C to keep the leaf temps at 28-29°C. Because LED has no infrared ambient temps = leaf temps(within 1°C). So to get optimal photosyntesis and leaf temps in the same range like with HPS we need to increase the ambient temps to ~29-30°C.
For this reason you need less air throughput, less AC and in the end you also save so CO2. With CO2 the optimal ambient temps are even higher and you can increase to 33-35°C. Sounds strange but when you test it out you'll see them exploding.
I like using pictures so here's another important one.. As you can see a plant getting 500μMol/s/m² at 30°C can outperform a plant getting 1500μMol/s/m² at 20°C.


The 2nd think is about the 4k spectrum. At first, there is nothing wrong with the spectrum itself. Both can grow huge plants! But if you look at the LM561c chart above and compare 3 and 4k you see 0,01 better PPF/w efficiency on the 4k spectrum but you get 0,06 more YPF/w from the 3k spectrum.
YPF/w performance literally shows you how well a plant can use a certain spectrum and in many, many tests here 3000°k has shown to be the most productive spectrum no matter if you use CRI70, 80 or 90. 3k will always win! Only a small number of the tested strains yielded better under the 4k spectrum but I think that had more to do with their genetic.

More compact growth is not always the best. With 4k the plants would stretch less and stay smaller compared to 3k and this can be counterproductive cuz the lower branches get less light with such a dense canopy. More stretch allows more light to travel deeper into the canopy leading to better sized side nugs.
I've started my white LED adventure ~5 years ago with 6 4k Bridgelux Vero18's and 4 4k/Vero29's. A year later I've build a more efficient light using 8 Cree CXB3590‘s in 3.500°k plus 40w of Osram deepreds. Than I've switched again to the 3000°k spectrum and my results have stadily improved. Today I'm using a mix of 3k/CRI80 strips and 3k/CRI93 COB's and I've added separate switchable strings of deep and far-red as well as two 24w UVB bulbs which run temporary for up to 2h per day. Far-red is used for end of day treatments to switch phytochrome far-red back into phytochrome red and put the plants immediately into night mode but its also used in the flowering stage to even out PS-I and PS-II efficiency. Because of the missing far red there is a difference in the efficiency of both photosyntesis systems. Deep-red will switch Phy-r into Phy-fr but with no far-red it stays in this stage. In natural sunlight the plants recieve both wavelength and the phytochromes are switched permanently from its active to its inactive stage. This has regulating effects and is a kind of balancer to keep both PS systems in balance. Far-red also have positive effects on leaf temps btw.
Below is a pdf if you're interested..

I also veg with 3k and the plants look like grown under natural sunlight. No unnatural stretch but short and compact growth and lots of early branches. It needs only ~10PAR/w of blue light per squaremeter to signal/suggest the plants they are in full sunlight and there is no need to stretch out.
3k has around 10% blue light so with a 50% efficient light you would need only ~200w to create enough blue light for compact growth on 1m². With a 5k spectrum you would need even less watts to keep the plants short and bushy so for energy savings in veg the higher spectrums are better siuted but as an all-in-one spectrum and especially for flowering 3k has proven to be the best.

Randomblame said:

but its also used in the flowering stage to even out PS-I and PS-II efficiency. Because of the missing far red there is a difference in the efficiency of both photosyntesis systems. Deep-red will switch Phy-r into Phy-fr but with no far-red it stays in this stage.

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According to the study by Shuyang Zhen and Marc W. van Iersel, the increase of the net photosynthetic rate reaches its lowest point at a certain PPFD (around 600 µmol/(m²*s) ) indicating that there is no more benefit from adding additional far-red light (see Fig. 4D). So in my opinion, it makes no sense of adding far-red light if you are operating at light densities higher than 500 µmol/(m²*s) and that is what most of the people here do. Even worse, the constant additional far-red radiation could introduce unwanted effects like increased stem elongination or increased leaf surface - energy that could go into the developement of colas.

sunsp0ts said:

I've also read some people say that anything over 35w/ft^2 is overkill with the LM561C

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35W/SF is arbitrary, it depends on how hard you are running the LEDs as there can be a 30+% difference in lumens per watt depending how hard hey are run

tomate said:

According to the study by Shuyang Zhen and Marc W. van Iersel, the increase of the net photosynthetic rate reaches its lowest point at a certain PPFD (around 600 µmol/(m²*s) ) indicating that there is no more benefit from adding additional far-red light (see Fig. 4D). So in my opinion, it makes no sense of adding far-red light if you are operating at light densities higher than 500 µmol/(m²*s) and that is what most of the people here do. Even worse, the constant additional far-red radiation could introduce unwanted effects like increased stem elongination or increased leaf surface - energy that could go into the developement of colas.

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Yeah, the effect gets smaller the higher you go similar to the emerson effect. But elongation, increased leaf surface and other signs of SAS depends on the amount of far-red you add. I'm using ~800μMol/s/m² at the tops and can measure half that much in the lower areas. This means maybe that not all parts use it to the same rate but I've not experienced bad effects from additional 20μMol/s/m² of far red and together with the far-red from the CRI80 and 90 mix its maybe twice as much total.
I'm using it also to control the stretch because its a way to communicate with the plant. But I see much more effect on elongation with increased EoD treatments.
Plants in nature get red and deep-red all day long and you see SAS only when the plants get more far- than deep-red for instance in the shade. As long as they get more deep than far-red there is almost no additional stretch.

Randomblame said:

I'm using ~800μMol/s/m² at the tops and can measure half that much in the lower areas.

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Ok, that makes sense, especially considering the fact that the FarRed light can even reach those lower branches because a good portion of this light gets transmitted and not absorbed or reflected.

Randomblame said:

As long as they get more deep than far-red there is almost no additional stretch.

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The ratio should be at least 3:1 or even higher if I remember correctly.

Randomblame said:

But I see much more effect on elongation with increased EoD treatments.

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How many µmol/m² of FarRed do you give your plants at EoD treatment and at which amount do you see a significant increase in stem elongination?
I know that there are numbers flying around ranging from 2000 to 4000 µmol/m². A user on an other forum gives his plants a crazy amount of 16000 to 26000 µmol/m² as EoD treatment and he swears that there is no noticable, additional stretch.

tomate said:

Ok, that makes sense, especially considering the fact that the FarRed light can even reach those lower branches because a good portion of this light gets transmitted and not absorbed or reflected.


The ratio should be at least 3:1 or even higher if I remember correctly.


How many µmol/m² of FarRed do you give your plants at EoD treatment and at which amount do you see a significant increase in stem elongination?
I know that there are numbers flying around ranging from 2000 to 4000 µmol/m². A user on an other forum gives his plants a crazy amount of 16000 to 26000 µmol/m² as EoD treatment and he swears that there is no noticable, additional stretch.

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so what do you say about Randomblame's mentioning of the Emmerson-effect? Do you now believe it's based on Far Red?