How far to keep your LED's / Quantum Boards from the canopy?

Blossom21

Active Member
This question about lights is probably as old as the first people who started to grow weed with electricity, and has been asked tons of times here too without end in sight. I didn't see a "real dedicated" topic about it either so decided to make one. Maybe some official or unofficial infotopic would be nice, unless it already exists and i'm just unaware. But if there isn't, maybe this topic would be a good start and very useful to especially newer growers like me who owns LED's.

I'm sure there's lots of studies about lights and how much plants (and this case weed) can absorb and use, and how much is too much or too little, and most importantly, what's the optimal amount of light to give your plants. And also i'm sure there's other must know things you have to keep in mind when trying to optimize how much light your plants can use, would love to hear about those too. I'm sure many of you are about min-maxing your setup as much as possible as i am, so i'd like to learn everything about this topic.

And if people would like to share their own setup, including their growing space and light distance/power from seed to harvest, and optionally their own personal experiences for example if someone managed to burn their buds with LED lights.

Lately i was a little bit confused when i saw my buddies 240w QB blasting at full power like 8-9" (20-23cm) from the canopy. I was like wtf, pretty much everyone i've asked and all sites tell to keep your LED's 18-28" (46-71cm) away from the canopy without much other information. He seems to be doing well, i saw his fat buds growing and my own look so thin compared to them. I started growing the same time as him, but i listened to someone's advice and kept my Quantum Boards way too high with little power, so vegging time was pretty long as you can imagine. And i even kept the boards at low power into flower too, after seeing my buddies setup i realized how far behind i am and adjusted my lights much more in hopes to get better results of course.

My setup:

4x4x6.5 (120x120x200cm) tent, a little over 500W total power shared with 4 Quantum Board so 125w per board, and one plant under each board in 5 gallon (19 liter) pots. Managed to train them enough to fill the tent from wall to wall, starting day 40 in flower now. My lights are currently at 14"-16" (35-40cm) away from the tops at about 75-80% power. Temps at day have been lately around 82-84F (28-29c) and humidity 50-53%. It's like 2f (1.5c) hotter at the canopy level, i think that's pretty normal right under the light. I was doing some testing and reading about VPD too, i'm out of the optimal zone because of the high temps/lower humidity that the plants would really want, but that's another topic.

I see in youtube videos people having expensive meters to measure light levels when testing lights, probably would be waste of money to get one of those just for this purpose, unless you know some cheap meter that would work well, and what kind of readings i should be aiming at?

Some of you guys must have perfected the craft and know everything about the topic for sure, what should i do about the lights at the moment? And is there some kind of easy/cheap way to measure the lights on top of charts what are optimal levels in different stages, so i would never have play any guessing games again. That would ease my life so much and i'm not the only one! Also how do you notice if the lights are a little bit too close, what signs should i be looking for?

And of course i'm trying to adjust my temps/humidity at the same time as close to the perfection i can. Even planning to get some extra deep red LED's (and maybe some kind of UV too if the cost/performance is worth it), there's so much studying to do but i've read/seen they really make a difference compared to just plain white Quantum Boards :)
 

BobThe420Builder

Well-Known Member
Big difference in the bds themselves, and distance suggested.
Spectrum effects it a lot, 2700k vs 4500k, way different
288bds vs a 132 or 120bds, also big difference.

I run my 288bds, 4000k, in veg anywhere from 16-24" away, depends on age.

My 132bds, 2700k, Ive had as close as 6" away, but try to stay 8-12" away

Always at 100% power


So Lots of factors at play here
 

Blossom21

Active Member
Big difference in the bds themselves, and distance suggested.
Spectrum effects it a lot, 2700k vs 4500k, way different
288bds vs a 132 or 120bds, also big difference.

I run my 288bds, 4000k, in veg anywhere from 16-24" away, depends on age.

My 132bds, 2700k, Ive had as close as 6" away, but try to stay 8-12" away

Always at 100% power


So Lots of factors at play here
Mine are all 3000K, 288xLM301B boards. Had no idea spectrum would have effect on it (and how much?), is there a source i could read/watch about it more too?

With that information what would you suggest if i take your word at face value :)
 

Kaotic

Well-Known Member
This question about lights is probably as old as the first people who started to grow weed with electricity, and has been asked tons of times here too without end in sight. I didn't see a "real dedicated" topic about it either so decided to make one. Maybe some official or unofficial infotopic would be nice, unless it already exists and i'm just unaware. But if there isn't, maybe this topic would be a good start and very useful to especially newer growers like me who owns LED's.

I'm sure there's lots of studies about lights and how much plants (and this case weed) can absorb and use, and how much is too much or too little, and most importantly, what's the optimal amount of light to give your plants. And also i'm sure there's other must know things you have to keep in mind when trying to optimize how much light your plants can use, would love to hear about those too. I'm sure many of you are about min-maxing your setup as much as possible as i am, so i'd like to learn everything about this topic.

And if people would like to share their own setup, including their growing space and light distance/power from seed to harvest, and optionally their own personal experiences for example if someone managed to burn their buds with LED lights.

Lately i was a little bit confused when i saw my buddies 240w QB blasting at full power like 8-9" (20-23cm) from the canopy. I was like wtf, pretty much everyone i've asked and all sites tell to keep your LED's 18-28" (46-71cm) away from the canopy without much other information. He seems to be doing well, i saw his fat buds growing and my own look so thin compared to them. I started growing the same time as him, but i listened to someone's advice and kept my Quantum Boards way too high with little power, so vegging time was pretty long as you can imagine. And i even kept the boards at low power into flower too, after seeing my buddies setup i realized how far behind i am and adjusted my lights much more in hopes to get better results of course.

My setup:

4x4x6.5 (120x120x200cm) tent, a little over 500W total power shared with 4 Quantum Board so 125w per board, and one plant under each board in 5 gallon (19 liter) pots. Managed to train them enough to fill the tent from wall to wall, starting day 40 in flower now. My lights are currently at 14"-16" (35-40cm) away from the tops at about 75-80% power. Temps at day have been lately around 82-84F (28-29c) and humidity 50-53%. It's like 2f (1.5c) hotter at the canopy level, i think that's pretty normal right under the light. I was doing some testing and reading about VPD too, i'm out of the optimal zone because of the high temps/lower humidity that the plants would really want, but that's another topic.

I see in youtube videos people having expensive meters to measure light levels when testing lights, probably would be waste of money to get one of those just for this purpose, unless you know some cheap meter that would work well, and what kind of readings i should be aiming at?

Some of you guys must have perfected the craft and know everything about the topic for sure, what should i do about the lights at the moment? And is there some kind of easy/cheap way to measure the lights on top of charts what are optimal levels in different stages, so i would never have play any guessing games again. That would ease my life so much and i'm not the only one! Also how do you notice if the lights are a little bit too close, what signs should i be looking for?

And of course i'm trying to adjust my temps/humidity at the same time as close to the perfection i can. Even planning to get some extra deep red LED's (and maybe some kind of UV too if the cost/performance is worth it), there's so much studying to do but i've read/seen they really make a difference compared to just plain white Quantum Boards :)
Try 26 inches first then see how your plants like it, done.
 

Kaotic

Well-Known Member
If it likes its and it seems to be growing vigorously but the leaf don’t look dry and brittle or browning getting cooked then lower a couple or few more inches, done.
 

BobThe420Builder

Well-Known Member
Mine are all 3000K, 288xLM301B boards. Had no idea spectrum would have effect on it (and how much?), is there a source i could read/watch about it more too?

With that information what would you suggest if i take your word at face value :)

Veg or flower?

Guess I mentioned veg with 288s, but not 3000k. Probably try 16", see how they respond


In flower, I'd do the same. Start at 16", see how they do. 12" may be too close, but worth a try


All I use are QBs , great lights
 

Kaotic

Well-Known Member
I wouldn’t go too close and risk actually frying the top leaves I would try higher than that and gradually go down, it’s a safer method
 

Kaotic

Well-Known Member
It’s a SF4000 which is ok not bad, what I’m saying is my method is safer than starting close then going up simple fact
 

Kaotic

Well-Known Member
Plus you don’t know how your strain of plants are gonna like all that light they all differ.
 

Kaotic

Well-Known Member
This question about lights is probably as old as the first people who started to grow weed with electricity, and has been asked tons of times here too without end in sight. I didn't see a "real dedicated" topic about it either so decided to make one. Maybe some official or unofficial infotopic would be nice, unless it already exists and i'm just unaware. But if there isn't, maybe this topic would be a good start and very useful to especially newer growers like me who owns LED's.

I'm sure there's lots of studies about lights and how much plants (and this case weed) can absorb and use, and how much is too much or too little, and most importantly, what's the optimal amount of light to give your plants. And also i'm sure there's other must know things you have to keep in mind when trying to optimize how much light your plants can use, would love to hear about those too. I'm sure many of you are about min-maxing your setup as much as possible as i am, so i'd like to learn everything about this topic.

And if people would like to share their own setup, including their growing space and light distance/power from seed to harvest, and optionally their own personal experiences for example if someone managed to burn their buds with LED lights.

Lately i was a little bit confused when i saw my buddies 240w QB blasting at full power like 8-9" (20-23cm) from the canopy. I was like wtf, pretty much everyone i've asked and all sites tell to keep your LED's 18-28" (46-71cm) away from the canopy without much other information. He seems to be doing well, i saw his fat buds growing and my own look so thin compared to them. I started growing the same time as him, but i listened to someone's advice and kept my Quantum Boards way too high with little power, so vegging time was pretty long as you can imagine. And i even kept the boards at low power into flower too, after seeing my buddies setup i realized how far behind i am and adjusted my lights much more in hopes to get better results of course.

My setup:

4x4x6.5 (120x120x200cm) tent, a little over 500W total power shared with 4 Quantum Board so 125w per board, and one plant under each board in 5 gallon (19 liter) pots. Managed to train them enough to fill the tent from wall to wall, starting day 40 in flower now. My lights are currently at 14"-16" (35-40cm) away from the tops at about 75-80% power. Temps at day have been lately around 82-84F (28-29c) and humidity 50-53%. It's like 2f (1.5c) hotter at the canopy level, i think that's pretty normal right under the light. I was doing some testing and reading about VPD too, i'm out of the optimal zone because of the high temps/lower humidity that the plants would really want, but that's another topic.

I see in youtube videos people having expensive meters to measure light levels when testing lights, probably would be waste of money to get one of those just for this purpose, unless you know some cheap meter that would work well, and what kind of readings i should be aiming at?

Some of you guys must have perfected the craft and know everything about the topic for sure, what should i do about the lights at the moment? And is there some kind of easy/cheap way to measure the lights on top of charts what are optimal levels in different stages, so i would never have play any guessing games again. That would ease my life so much and i'm not the only one! Also how do you notice if the lights are a little bit too close, what signs should i be looking for?

And of course i'm trying to adjust my temps/humidity at the same time as close to the perfection i can. Even planning to get some extra deep red LED's (and maybe some kind of UV too if the cost/performance is worth it), there's so much studying to do but i've read/seen they really make a difference compared to just plain white Quantum Boards :)
Also only a few lights have UVB or at that UVA, make sure you don’t stay under those lights for so long and wear safety glasses btw
 

Kaotic

Well-Known Member
Sf4000 is a lot different than 288bds

You are correct, but he is looking for real life practice which I'm giving him
That is a real life practice lol, you ask any grower, they will tell you to first start high then gradually lower down, especially with led rays they are stronger than hps rays even though hps produce more heat so therefore having any light too close is bad
 

Kaotic

Well-Known Member
He’s only able to run it lower because it is a weaker light the spectrum rays aren’t as strong simple. It depends on the type of light you have, but practicing the method of starting any light high then gradually lowering is better than starting anywhere too low for your plants likings and frying, that’s my point.
 

Blossom21

Active Member
Veg or flower?

Guess I mentioned veg with 288s, but not 3000k. Probably try 16", see how they respond


In flower, I'd do the same. Start at 16", see how they do. 12" may be too close, but worth a try


All I use are QBs , great lights
They're 40 days in flower now, as i mentioned in my OP.
 

Blossom21

Active Member
Try 26 inches first then see how your plants like it, done.
The only time i was that high was in veg and start of flower, then i lowered them a little bit to 18-20" after a while in flower and added power too. My buddy has the same quantum board than me, "only" 240w tho but he's running it 100% at lower than 10" from the canopy, and his plants are like at F55, while mine are F40.
 

Kaotic

Well-Known Member
They're 40 days in flower now, as i mentioned in my OP.
He’s only able to run it lower because it is a weaker light the spectrum rays aren’t as strong simple. It depends on the type of light you have, but practicing the method of starting any light high then gradually lowering is better than starting anywhere too low for your plants likings and frying, that’s my point.
And if you see any white skinny
The only time i was that high was in veg and start of flower, then i lowered them a little bit to 18-20" after a while in flower and added power too. My buddy has the same quantum board than me, "only" 240w tho but he's running it 100% at lower than 10" from the canopy, and his plants are like at F55, while mine are F40.
yes you can keep lights lower for flowering it’s better for them, but just be sure to not to have them too close, I’ve had that problem once and my gelato plant gave me like 3.5 oz instead of a whopping 5 to 6.
 
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