Optimum Spectrum for Veg?

I bet 6-8 6500K cfl with hoods can veg the shit out of a plant for
4 weeks, keep node spacing tighter than a fungus gnats asshole lol

No additional lighting needed.

Moreso than the red stem the tell that they are unhappy is all 3 finger leaves. My clones would only throw 3 finger leaves under my 5k LED for the first week. Then lime green vegetation, red stems, just not looking as verdant as I wanted. I got my light down to 10 w/sqft, 30" away, tried epsom salts, pH drift higher and lower, etc. Nothing really worked. I switched to flouro 6400k and same genetics, same nutrients, same environment clones started throwing lush green 5 finger leaves immediately after rooting.
here is a pic of my veg room when it was under LED:

They eventually grow into the light and throw 5 and 7 finger leaves but you can see how dark the stems are and how the leaves just have a pale green color to em.
here are clones of the same cut in the same room, same general environment, same type feed (not same exact EC), same pH, ect after i switched to flouros:

To be clear the final product in both of these grows did not differ significantly whatsover. I don't think veg is important, just gotta provide basic needs and keep em as happy as possible. I don't think there is some sort of "LED deficiency" or anything like that, just for whatever reason it's harder for me to keep cannabis plants happy in veg with LED. Also to be clear I happily flower under LED.

pulpoinspace said:

I don't think there is some sort of "LED deficiency" or anything like that, just for whatever reason it's harder for me to keep cannabis plants happy in veg with LED.

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Well, a CFL's spectrum is much broader in the Near-UV/blue range where alot of photoreceptors and stuff has its absorption peaks. I'm always impressed with the beautifulness of CFL grows - there was a guy once here on RIU which would use 1000w t8 in flower and had stunningly healthy plants - fully outripen. The stimulation of the receptors may follow a photomorphogenic response, I find that quite logical and one can see that in experiences like yours somewhat easily...

The LED plants leaf color is mostly due to the "false-spectrum" picture. High K diodes create their spectrum via an insense almost monochromatic spike in 440nm, leaving 380-420nm, and 470-490nm out, and also placing less emphasis on green. But a CFLs spectrum rather has spikes everywhere.

I've also noticed that when one additionally exposes plants to UV, their leaves tend to "pray" more. And just look better generally, and looking happy always grows strongest. But a grow consists of many variables, so can there be an absolute answer? But seriously, I have seen this type of weak 3-fingered leaves in a number of reports always under LED spectrum, and since then always wondered if that could be spectrum related?

Kassiopeija said:

Well, a CFL's spectrum is much broader in the Near-UV/blue range where alot of photoreceptors and stuff has its absorption peaks. I'm always impressed with the beautifulness of CFL grows - there was a guy once here on RIU which would use 1000w t8 in flower and had stunningly healthy plants - fully outripen. The stimulation of the receptors may follow a photomorphogenic response, I find that quite logical and one can see that in experiences like yours somewhat easily...

The LED plants leaf color is mostly due to the "false-spectrum" picture. High K diodes create their spectrum via an insense almost monochromatic spike in 440nm, leaving 380-420nm, and 470-490nm out, and also placing less emphasis on green. But a CFLs spectrum rather has spikes everywhere.

I've also noticed that when one additionally exposes plants to UV, their leaves tend to "pray" more. And just look better generally, and looking happy always grows strongest. But a grow consists of many variables, so can there be an absolute answer? But seriously, I have seen this type of weak 3-fingered leaves in a number of reports always under LED spectrum, and since then always wondered if that could be spectrum related?

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Definitely could be elements of all of that going here. It's not just the picture tho the plants were noticeable harder to keep happier in all stages of veg. I just didn't save that many pictures of how shitty they looked. I would think 3 finger leaves is just a sign of stress in general, spectrum could play a role, but I think my problem was mostly intensity. I built a 200w veg lamp for my 2x4 and I was consistently dimming it down more and more and trying to keep it further away. My ambient temps might just be a bit low. 5k LEDs are super efficient. My 200w t5s provide maybe half as much light and the other half of the power is converted to heat haha

pulpoinspace said:

Definitely could be elements of all of that going here. I would think 3 finger leaves is just a sign of stress in general, spectrum could play a role, but I think my problem was mostly intensity. I built a 200w veg lamp for my 2x4 and I was consistently dimming it down more and more. My ambient temps might just be a bit low. 5k LEDs are super efficient. My 200w t5s provide like half as much light and the other half of the power is converted to heat haha

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The experience of me and some others is that when light is too scarce it'll not fully form the 2 from the 5. See that with clones consistently. And the opposite - 11 to 13 fingers - only in outdoor. Now the midday sun is both plenty in blue and unrivaled in strength.

i think intenisty is the main point, i really had my problems there.
in the end i am at maybe 5W a sqaure foot, while my cxb3590 are a bit close, too close, can cause bleaching easily (you can see the upper most leaves near to the cob starting to get pale).
3 finger leaves are not a basic problem of leds.
i get 3 fingered ones from mothers kept in 1l pots cut down every 1-2 weeks, theyre simply not in perfect shape.
it takes 2-3 weeks till theyre over it and start to throw 5 finger leaves (under led of course, 3k , 5k, doesnt matter).
from seeds they look like this, also just 18W 6500K led light.
almost a year ago (same genetics, one is the mother of the 3 finger clones).


3 fingered clones after a few weeks of led light, 3000k, well ok, plus some 365nm 1.5h a day (no idea how big the influence is).


i do second somehow that a lower blue region should be covered, and/or some uva, also think they pray more/easier.
thats why if i would have the choice, i would tend to higher kelvins for veg.

pulpoinspace said:

Moreso than the red stem the tell that they are unhappy is all 3 finger leaves. My clones would only throw 3 finger leaves under my 5k LED for the first week. Then lime green vegetation, red stems, just not looking as verdant as I wanted.

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This definitely concerns me.

But let's be clear, LED like Fluorescent is just a specific technological means of emitted electromagnetic waves in the visible spectrum (not including UV). There is nothing inherently different between LED and Fluorescent in terms of the "light", so whatever plant issues one is having with either one is a matter of the light spectrum used and intensity. In other words, there is no way LED in and of itself is the problem. The problem lies in the spectrum and intensity. But I do get what you and Cobbshop are saying about the potential difficulty of "dialing it in" with LEDs, which I would rather not have to deal with.

I wasn't going to mention this because there are other factors involved, but I currently have 2 x 2x4 EB gen3 CRI90 4000k lights in veg, and I'm having some issues that look like over watering. But I'm glad for the input here because I'm doing 19w per sq ft at 20 inches from canopy and just understanding that this is way too strong. I've got the "A" version driver so I just backed down the current and moved the lights higher. But the cri90 4k spectrum has max blue and not as much red so maybe that is too much blue? We can only guess about these questions because there is not enough data or experience to really say for sure.

Obviously, the spectrum of the sun in spring is great for plant veg, and that is what I liked about the CRI98, they are touted as being close to natural light, but they don't have UV so maybe that is a big factor. The spectrum of those 5k CFL doesn't look like it would be very good for veg at all, it is most intense in the green, with little blue and a lot of red, although it does have some UV. And I'm sorry Kassio but it does not have "spikes everywhere". But if it is working in veg then I guess the proof is in the pudding.

I could go on speculating about what would be the perfect spectral range but I'm giving myself a headache about it. I'm just going to try and get things dialed in with my cri90 4k before I go buying anything else at this point.

tilopa said:

But I'm glad for the input here because I'm doing 19w per sq ft at 20 inches from canopy and just understanding that this is way too strong. I've got the "A" version driver so I just backed down the current and moved the lights higher.

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It's no replacement for a PAR meter, but a $15 lux meter can be quite useful.

i doubt your 4000k 90cri have too much blue, looking at their spectrum they offer way more more red then blue.
i dont have the same strips but i also use 4000k cri95 buddies which really produce nice healthy plants.
a good portion of blue in veg dont hurt them in my eyes.
i seldon have optimal temps and may other factors arent optimal, but it could be its a bit easier to produce a healthy plant with a spectrum more rich in blue.
the thrive you have choosen (5700k a tiny bit more then 5000k) is one of the most sunlike spectra i saw, basically it should work well.

biggest influence is clearly the intensity if we compare cfl to led we see that cfl gives a 50-70 lumen per watt, modern daylight leds are almost 200 lumen per watt.
so about 3 times as much light emitted b< the leds compared to cfl !
then the cfls have a big spike in the green, exactly where the lux meter measures, so the lux is may even in favor for the cfls, ppfd wise the led should be even better as it offers more in the par favored regions, making it even "worse".

1212ham said:

It's no replacement for a PAR meter, but a $15 lux meter can be quite useful.

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Good tip. I just bought one, opted for the $30 one.

cobshopgrow said:

then the cfls have a big spike in the green, exactly where the lux meter measures, so the lux is may even in favor for the cfls, ppfd wise the led should be even better as it offers more in the par favored regions, making it even "worse".

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You lost me here. Sorry to ask you to explain but I really value your knowledge and don't want to miss anything.

Do you think having my leds at 19w per sq ft at 20 inches could have been the cause of my problems of these plants not doing well with leaves curling down like over-watered symptoms?

cobshopgrow said:

i doubt your 4000k 90cri have too much blue, looking at their spectrum they offer way more more red then blue.

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You are right, my mistake. I was just noticing that the blue spiked to 100% at some point, but overall there is definitely more red.

I chose the 5000k, I think the 5700k was mentioned somewhere else. But they both look good. But, I was wrong to suggest that the Thrive have a spectrum close to the sun, that is EB marketing. I looked at a spectrum graph of the sun and it has way more of everything basically. However, if you combine the thrive 5000k and 5700k you get pretty close to the sun.



But I'm still not sure I want to go that much blue. I've been reading that too much blue will cause the plants to be stunted, and have less vigorous (fast) growth. Prior to the LEDs I was using CMH lights, and even with the Phillips 4k bulb my plants would always stretch too much. No matter how much I pruned them back by the time they went to flower they would be tall lanky and floppy plants. This is a real problem because it is hard to get them to cover the canopy and it effects yield. So, the blue LEDs will fix this, but... I don't want it to be too much in the other direction.

Having said all that I would consider a mix of 5000k and 5700k but I cannot find the 5700k anywhere available. I'm in the US.

tilopa said:

You lost me here. Sorry to ask you to explain but I really value your knowledge and don't want to miss anything.

Do you think having my leds at 19w per sq ft at 20 inches could have been the cause of my problems of these plants not doing well with leaves curling down like over-watered symptoms?

Click to expand...

i have no ppfd /W numbers for a cfl at hand, but have in mind that a lux meter measures mainly the green , if your lamp is strong in f.e. 660nm it wont be reprensented well in the lux measurement, same for blue.
a peak in green give you high lux readings, as thats what is measured by a lux meter.
basically just wanted to say that the led may put out even more usable light for the plant then the cfl does which isnt showen by the lux value.

well ijust know my little enviroment a bit, i wont be able to give 19W on a square feet during veg, that would give me lots troubble.
things could be different for you of course, but i would try to reduce the intensity if you encountered problems, yes it could be a part if it.

the 5000 kelvin looking good to me, they really should work good.
its at least a better veg spectrum on paper to what most of us use here, myself of course included.

sounds like you will know soon whats working the best for compact plants, i hope you share some infos.
if 4000k dont do it for you, going with 5000k is a logical consequence.

oh, one tip to dial in the intensity.
see how droppy your plants are 3,2,1h before lights out.
if they really sag 3h before end of day, they sawn too much photons allready.
when they pray till the end of the day they could have taken clearly more.
along these lines one can dial in the intensity, they should pray most of the time.
if theyre blasted too much sometimes they never get in pray mode over the day.

tilopa said:

You are right, my mistake. I was just noticing that the blue spiked to 100% at some point, but overall there is definitely more red.

I chose the 5000k, I think the 5700k was mentioned somewhere else. But they both look good. But, I was wrong to suggest that the Thrive have a spectrum close to the sun, that is EB marketing. I looked at a spectrum graph of the sun and it has way more of everything basically. However, if you combine the thrive 5000k and 5700k you get pretty close to the sun.

View attachment 4785090

But I'm still not sure I want to go that much blue. I've been reading that too much blue will cause the plants to be stunted, and have less vigorous (fast) growth. Prior to the LEDs I was using CMH lights, and even with the Phillips 4k bulb my plants would always stretch too much. No matter how much I pruned them back by the time they went to flower they would be tall lanky and floppy plants. This is a real problem because it is hard to get them to cover the canopy and it effects yield. So, the blue LEDs will fix this, but... I don't want it to be too much in the other direction.

Having said all that I would consider a mix of 5000k and 5700k but I cannot find the 5700k anywhere available. I'm in the US.

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Seoul has the sunlike diodes that seem to have a nice spectrum too. They are a bit more expensive and less efficient than the thrive's, but they bring a pretty balanced spectrum starting a bit more in the near-uv range. Adding some of these to your 4k 90cri strips may be a nice combo without going too deep into the blue's. I don't own any of these, but keep thinking about grabbing a few to work into some other strip/board build (too many components still sitting in boxes already not being used at the moment though). I also saw hlg will be offering some sort of strip using this same spectrum soon too.


I'm far from experienced in any of this, so take what I say with a grain of salt, just my two cents. I just enjoy trying to figure out that "perfect" spectrum as well and get lost in the datasheets and graphs as well. I agree with @cobshopgrow though, seems like the 90cri 4k strips could be just fine if you found that sweet spot though. Best of luck with everything and hope it all improves to your liking soon.

@pulpoinspace @cobshopgrow a little offtopic about clones. You have great looking clones. I wonder if you have some journals or pictures of week by week till harvest? I was asking in other thread about cloning, I am new to it, and I wanna see some progress to see if it's worth it and how to properly setup grow room by growth. So, any journals or pictures week by week? We can also move on PM if you wish.

KonopCh said:

@pulpoinspace @cobshopgrow a little offtopic about clones. You have great looking clones. I wonder if you have some journals or pictures of week by week till harvest? I was asking in other thread about cloning, I am new to it, and I wanna see some progress to see if it's worth it and how to properly setup grow room by growth. So, any journals or pictures week by week? We can also move on PM if you wish.

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I have a link to my journal in my signature. its not exactly weekly updates but there are lots of pictures there. you can post in that thread too if you have any questions. cloning is very easy and definitely the way to go. I use a very basic cloning technique with rockwool/clonex and a humidity dome.

i seldon make pictures when i clone, i do really nothing special.
rooting powder, some rooting cubes in to a greenhouse with high humidity so they surivve a few days without roots.
as long i dont drown them they give roots.

I dont get why noone has mentioned Vesta strips with regards to this.
2 channels in 90 cri, 5000k and 2700k with same voltage. With both channels on you get something like a 3700k 90cri spectrum. 200 diodes for a tenner or so.

If you wanna finnese it more you can use 2 dimable drivers and just dial in the amount of red/stretch/node distance you want.

I recently built a vesta based light for an auto grower and the light worked great from germination to finish.

They are a bit on the low side of efficiency, bxeb gen1, but large diode count and the flexibility it offers goes a long way