3500k vs 4000k vs 5000k ?

After a ton of research and COB sourcing and looking for this specific question I am puzzled.

So here goes.

From what I can see from the Cree CXB datasheets or any COB datasheet the 5000k is by far the highest lumen output while the 3500k is much lower and the 4000k just a bit higher. However spectrum comes into play, but from what I can tell the major COB builders belive photos over spectrum. If this were true why would we not hust use blue as it has the highest output?

Has anyone done a grow of 5000k all the way though? I would also love to know any differances from 3500K vs 4000k.
Ill be picking up alot of COBS here soon from a supplier and testing myself but would love to see what users here have to say on this.
I am well aware we want umol/J and lumens are just a starting point.
There is alot of data around here but none has ever been tested in a sphere so I cannot take it as 100% as numbers vary in practice.


Cheers,Trippy

Jump in greengenes thread back when he was still rocking an AT600, he did a side by side of 3k cxbs, 4ks, and the AT and the 4k ended up looking the best personally (frost for dayyyyyyys) doesn't mean that's the right answer, there is no right answer, but results speak for themselves- and they all deliver.

Scotch089 said:

Jump in greengenes thread back when he was still rocking an AT600, he did a side by side of 3k cxbs, 4ks, and the AT and the 4k ended up looking the best personally (frost for dayyyyyyys) doesn't mean that's the right answer, there is no right answer, but results speak for themselves- and they all deliver.

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Have seen that video. The 4000K looked better for sure. Seems like the more blue helped. I wonder how a 5000K would do. Personally I would go with 4000K over 3500 but maybe 5000k would give something interesting.

Straight 4000k flowers smaller, denser, frostiest nugs Ime. It's better to mix 3000k and 4000k. The 3000k seems to elongate the nugs while the 4000ks keep the density and frost up. Both spectrums work awesome on their own, but the mix has worked best for me.


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kmog33 said:

Straight 4000k flowers smaller, denser, frostiest nugs Ime. It's better to mix 3000k and 4000k. The 3000k seems to elongate the nugs while the 4000ks keep the density and frost up. Both spectrums work awesome on their own, but the mix has worked best for me.


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Did mixing them help with yields?

Trippyness said:

Did mixing them help with yields?

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I'll know in about 2 weeks. Looks like maybe a bit. Not a huge difference if any. But the plant/bud structure is nicer. Much frontier on the 4000k heavy side.


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^^under 5k+670

Edit added another

Scotch089 said:

View attachment 3694390 View attachment 3694393

^^under 5k+670

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Thats some super frost there. Just running 5k? Start to finish? Whats your setup? You used any other CCT and if so how do you like 5000K? I am very interested in 5000K

45-80w of 5k in veg (~2x3')

then 8x 5k cobs @350ma and 19x xpe photo reds (665-670nm @700ma)

That run was 127w through flower.

I've used...ufos...progrows...old a51s (4250k, and 3k)... sgs160... AT200... diy with its base made of 8x cxa 3k ABs with xml2s and reds, and now this setup.

Probably won't be changing anytime soon, if I do it'll be to split the panel in half of 3k and 5k and do a side by side, but I don't have that kind of time

Scotch089 said:

45-80w of 5k in veg (~2x3')

then 8x 5k cobs @350ma and 19x xpe photo reds (665-670nm @700ma)

That run was 127w through flower.

I've used...ufos...progrows...old a51s (4250k, and 3k)... sgs160... AT200... diy with its base made of 8x cxa 3k ABs with xml2s and reds, and now this setup.

Probably won't be changing anytime soon, if I do it'll be to split the panel in half of 3k and 5k and do a side by side, but I don't have that kind of time

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Nice, whata the main differance you are seeing with the 5k plus photo reds as oposed to the other sub 4000k fixtures? Seems like you got the bulk and frost for days.

But keep in mind, GG just had a stupid amount of frost on his rift under 3.5k. I like 5k and red but I'm not producing massive numbers to take to shops or setting records, just making sure I can keep smoking some grade A ganga.

I noticed more drawn out structure and a tendency to foxtail easier under warmer Kelvin, I like to keep my bitches stout. With the amount of blue in 5k, my reds are no worry. I think I just got lucky with my rough estimates though (amount of red), definitely used the sgs and at200 as a baseline.

Keep in mind too, it's more tedious work incorporating reds that may not feel worth it when you can pull similar results with all 3.5k. I totally understand that train of thought, but I'm diehard I s'pose

As someone looking to eventually go in this direction, Thanks!! This is awesome info. Those Girls look beautiful too.

Thanks dude but keep looking around, I'm not trying to come in here and say it's the absolute best most ideal perfect spectra. Look at everyone's results under different combos and decide what you think will work best for you or what you think the plants want. It's not black and white.

I urge everyone else to throw up pics under different Kelvin and come together instead of standing on other sides of the field scrutinizing. (Just don't say monos are useless )

kmog33 said:

I'll know in about 2 weeks. Looks like maybe a bit. Not a huge difference if any. But the plant/bud structure is nicer. Much frontier on the 4000k heavy side.


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Cant wait to see what you come up with be sure to share

Scotch089 said:

Thanks dude but keep looking around, I'm not trying to come in here and say it's the absolute best most ideal perfect spectra. !

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Yeah I appreciate that. But it is something I had been thinking about myself as far as what the results and differences would be. I have looked at a lot of the 3500k builds and grows and they are amazing. Just not seen many K variations so its good to see someone going through different combos and noting on here the outcome and personal observations. Top work

Scotch089 said:

Thanks dude but keep looking around, I'm not trying to come in here and say it's the absolute best most ideal perfect spectra. Look at everyone's results under different combos and decide what you think will work best for you or what you think the plants want. It's not black and white.

I urge everyone else to throw up pics under different Kelvin and come together instead of standing on other sides of the field scrutinizing. (Just don't say monos are useless )

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Monos are not useless at all. Single diodes have some killer efficiency such as xpg3 but price per umol/j is more than COB. Wiuld love to see some more comments under differant kelvin.

Main goal is yield and potency. I see so much more frost under 400K and 500 than 3500. I wonder how adding UV diodes to a 3500K would help with that.

I am only a couple weeks in testing CRI, but it is also between 4000k 80cri and 3200k 95+cri. Still the only difference I see is the amount of stretch and the sun leaves are larger under the 95+. So far those are the only differences I can see. Do you guys see anything different?

Scotch089 said:

I urge everyone else to throw up pics under different Kelvin and come together instead of standing on other sides of the field scrutinizing. (Just don't say monos are useless )

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While you can grow with damn near any light, I think most here would agree we have not identified the perfect spectrum for cannabis yet and until we do (and a manufacturer begins making COBs for that spectrum) there will be a place for monos. Much closer than we were just 10 years ago, but there is a paucity of hard number tests with sufficient proper controls to definitively create what would maximize quality and quality. (How much 730 nm and for how long? How much UVB 280-300, when and for how long? Does UVB adversely effect yield while enhancing resin production? Supplement with 700 and 670/680 for enhanced Emerson Effect or are the levels from the cob sufficient?)

Lots of work for us to do and lots of fun to be had discovering!

It wouldn't surprise me to find that there will be variations between strains and phenos, just as there is with nutes, so testing with single batch clones like @nevergoodenuf is doing, and repeating the experiments with different strains will be critical to evaluation. IMHO, right now cobs do come closest due to the broad spectrum and high efficiency, and because so many of the top growers here are seeing spectacular results with 3500k that will be my base build - and will test additional supplemental wavelengths from there. Used to be 2 choices MH or HPS, pretty simple back then: "Let's see, do I want to flower or veg...?" !