Quantum Boards burning plants.

I am trying to figure out why the QB's are burning (leaves curl, tips burn and curl down, dry, yellowing, interveinal chlorosis, rust spots) my plants/seedlings even though the lux and PFFD reading are at the lower end of the recommendation, yet my flowering plants are doing just fine as the buds are frosty as expected.

I have 2 x QB288 v1 3000k (from Meiju) and 2 x QB288 v3 with 660nm, 3500K (from Kingbrite) in a 4x4x7 tent.

I got two different strains flowering. The lights, 4 separate QB288 panels, are hung about 24" from the canopy and they are spread out for even lighting. They started flowering at around 14K LUX or 200 PPFD. I use the Lux to PPFD converter and later bought a PAR meter because of this issue. When I increased the intensity, using the dimmer, to around 28K LUX or 400 PPFD, just for one day, the plants burned severely. The next day and week, the cannopy turned yellow, the leaves droop and dry, interveinal chlrosis turning into rust spots, etc. In other words, they burned badly!

The range as recommended by HLG and other sources are:
vegging: 300-600 PPFD or 21K-42K LUX.
flowering: 600-800 PPFD or 48K-55k LUX.

So, this is very strange as those values I used above are well within tolerance for flowering plants as recommended.

Now, I'm in mid flowering and afraid to burn the leaves even more so the 4 x QBs are hung at 30" dimmed down to around 60% and light intensity of 18K LUX or 260 PPFD. I'm not even half way to the recommended vlaue of 600 PPFD for flowering. Yet, the buds are super frosty for being only in mid flowering and things are humming along even though the LUX and PPFD are way below the recommended range for flowering. The issue is just not happening with one strain as I have another strain in the tent that would burn too if I increase the LUX to 30K or higher.

I'm banging my head right now as I can't figure out what the hell is going on. Is it because I have 4 x QB288 and they multiply in intensity and thus cannot use the recommended range?

I really want to be able to get the light lower for better penetration to the lower bud sites. As of now, I am slowly increasing the intensity by 1K LUX every few days and keeping an eye out for droop and burn.

Anyone experienced something like this? No complaints about the frosty buds and growth, but the LUX/PPFD being way below the recommended range and the lights being hung so high is something I can't figure out.

Should have bought led specific strains..... Lol.

Are doing any foliar applications with lights on? Also higher ppfd, higher nutrient uptake .... Just guessing, cause I'm not in the grow room looking at your girls personally

Seems like you have other problems. I have run cobs closer than 24 without burning. Got some twisting and odd growth over 50w per square foot. But not burning you are talking about in a single night.

I recalled doing a foliar spray with the lights on because I don't believe that water droplet on the leaves with the lights on would burn the leaves. That's a garden myth. Look outside, it rains and then the sun come out, yet outdoor plants don't burn even in the high desert with intense summer sun light.

I have also raised a different strain closer to the light (at around 25K LUX) and it got burned instantly. The next day, this plant would droop and looked sad. A few days later, the big fan leaves would turn yellow and necrosis occurred. This plant was just transplanted to well cooked living organic soil with plenty of nutes. So, it was indeed light burnt and not cal/mag deficiency. I have also managed to burn seedlings in my veg tent even though the QB was turned down to like 25% and hung at 3 feet away. I am having such a hard time getting these QB's figured out.

It makes sense that plants grown under QB's need more nutes, especially cal/mag, due to higher intensity. But as I've explained in the OP, the light intensity is not anywhere near the recommended range.

Boatguy said:

Seems like you have other problems. I have run cobs closer than 24 without burning. Got some twisting and odd growth over 50w per square foot. But not burning you are talking about in a single night.

Click to expand...

Could the 660nm diodes be the culprit? During my first grow, I was using 2 X QB288 v1 without the 660nm diodes and did not experience any burnts during veg or flowering. Now that I added the new QB288's with 660nm diodes, I am burning anything under it easily if I don't watch the distance and intensity. What do you think?

Foliar is a broad term , wasn't taking about water...... But you're right, should have been more specific

Got any pics?

Unfiltered...
Let the light be your guide..

Just because another manufacturer gives you recommended light distances...doesnt mean its universal among manufacturers

In actual fact, one grower on RIU analyzed HLG vs some chinese equivalents and actually
measured a higher PAR value on the chinese lights..

Poke around in RIU and you should find it..

cheers
Toad

Temps, humidity, PPM, run-off (if applicable)?

Temps and humidity? These can really matter when it comes to led. Its usable/reasonable light, but something about the intensity. Temps and rh are too low and not enough transpiration. Can't keep up with water and nute demands.

IDK, I have a hard time believing that the light source/660nm is the culprit. I live on red/deep red based spds, never had any issues unless my plants touched the diodes.

Is this happening with just one specific strain? Or multi crop?

PSUAGRO. said:

Foliar is a broad term , wasn't taking about water...... But you're right, should have been more specific

Got any pics?

Click to expand...

Here's a pic.

The lighter color one is the one that's burned severely but I have managed to stop or slow down the damage. I got 4 more weeks to go so hopefully there's enough healthy leaves for photosynthesis so she would finish.

As for the greener plant (Super Lemon Haze) at the bottom, you can see the bigger fan leaves got burned when I raised it higher. Now, it's sitting at a lower/safe distance from burning hell.

PSUAGRO. said:

IDK, I have a hard time believing that the light source/660nm is the culprit. I live on red/deep red based spds, never had any issues unless my plants touched the diodes.

Is this happening with just one specific strain? Or multi crop?

Click to expand...

I have two strains in the same tent. The light burned both plants as explained in the OP.

MrToad69 said:

Unfiltered...
Let the light be your guide..

Just because another manufacturer gives you recommended light distances...doesnt mean its universal among manufacturers

In actual fact, one grower on RIU analyzed HLG vs some chinese equivalents and actually
measured a higher PAR value on the chinese lights..

Poke around in RIU and you should find it..

cheers
Toad

Click to expand...

Yeh, I learned this lesson. Always read stuff with grain of salt. And indeed, let the plants tell you what it wants/or not. So, maybe my concern with the OP is not such a big deal if I just go with what the plants say. But I am curious to see what others who have Chinese QBs think as reading with regards to LUX and PPFD is way off from others on here.

charsi420 said:

Temps, humidity, PPM, run-off (if applicable)?

Click to expand...

Day 25C, 65%, living organic soil, so don't know jack about ppm. I am very well versed with VPD and DLI, so believe my environment is acceptable. I've just put another plant in this flowering tent and it's praying all week and growing super healthy. But this plant is sitting on the ground, far away from the QB's, just to be safe until I figure out the optimal light intensity and distance.

R Burns said:

Temps and humidity? These can really matter when it comes to led. Its usable/reasonable light, but something about the intensity. Temps and rh are too low and not enough transpiration. Can't keep up with water and nute demands.

Click to expand...

See my reply above regarding environment. I believe I got VPD dialed in.

I meant plant...it will tell you.
Get a par meter and see how much your light cranking out

MrToad69 said:

I meant plant...it will tell you.
Get a par meter and see how much your light cranking out

Click to expand...

See the OP. Bought a PAR meter just for this issue. PAR reading is way below recommended range.

unfiltered said:

Day 25C, 65%, living organic soil, so don't know jack about ppm. I am very well versed with VPD and DLI, so believe my environment is acceptable. I've just put another plant in this flowering tent and it's praying all week and growing super healthy. But this plant is sitting on the ground, far away from the QB's, just to be safe until I figure out the optimal light intensity and distance.

Click to expand...

What have you fed them other than water in the last few weeks and in what amounts?

Could 4 QB's in the same tent affect the reading? When the HLG or other sources recommend the PPFD range, is that the general reading at the canopy and it doesn't matter how many QB's you have?

unfiltered said:

See my reply above regarding environment. I believe I got VPD dialed in.

Click to expand...

So then I would look to genetics. Specially how it processes/uses calcium. Also might just need more, but you seem to know what you're doing. They have weak cuticle, can't take the intensity. Have to work it like hardening off. I have this go on alot with moving to quantums from fluorescent. Some are a real pain in the ass about it.