Light stress ?

[Jimi O'Connor]

Two Death stars and a GODFATHER OG in the ac infinity 3×3. S33 Light. The plants a looking a little lighter green under the light and a little darker on on the outer edge.

Light stress? I have the ppfd app on my phone and I have the Uni-T meter also. Idk how accurate it is do you by chance?

Day 17 of flowering 12/12 cycle. Should I not worry or is the light to close?

 

[Delps8]

I see no indication of anything other than a well nourished cannabis grow. You've also pretty much grown out the canopy to cover the entire grow space. That's good to see—no photon is wasted.

The Uni-T is sufficiently accurate for most growers and, at 826µmol, you're about 200µmol below where I would run the grow.

Re. the accuracy of the Uni-T—it's "calibrated" to 5%± per their literature and I have no reason to not believe that. I tested the Uni-T in 11/23 and here are the results:



I compared the results from the Uni-T against my MQ-500 (calibrated) and determined the "conversion factor" for the light to be 0.0145 which seems to be "about right". "about right" is as close as I could get because I don't have much info on the XS-1500 spectrum but it's got more blue in it than the "average" white LED so 0.0145 is about right.

Is 0.0145 correct? It's close enough. As I see it, the primary goal of measuring PPFD is to get some idea of how much light is falling on the canopy and then let your plants tell you how much light they can use. The most obvious signs of a plant that is getting too much light are that the edges of the leaves will curl inward ("canoeing" or "tacoing") and in some cases leaves will rotate around the petiole in the same way that a Venetian blind opens and closes.

If you're fat 867 now, increase you input wattage by ~10% or lower the light by about 2". That will get you over 900µmol and that's a good number for cannabis.

My practice is to increase light levels in the morning and check the plants at 30 minutes and 60 minutes. If the new light levels are at or above the "light saturation point", the plants will let you know. Cannabis reacts very quickly so two checks, 30 and 60, should do the trick.

In ambient CO2, cannabis will thrive at 1kµmol, assuming that light is the limiting factor. If your grow is in good shape (temp+RH/VPD, adequate nutrient levels, properly watered) you should be able to put that much light on the plant.

The PPFD map for your light is shown here. As expected, the higher the light is above the canopy, the more even the lightcast. In a 3' x 3', there's enough light being generated that you can get ~1k in the center of the grow and still get good light around the edges.



At this point in the grow, your plants have completed most of the "building" process so it's about time to reduce ambient temperatures so that the tops of the buds are <78°. The graphic below is based on the research that Mitch Westmoreland did for his PhD (he was a student under Bruce Bugbee).

He released an excellent video on cannabis about 18 months ago. Check for it on YouTube. It's about an hour long and full of excellent information about getting the most out of a cannabis grow.

 

[Jimi O'Connor]

I see no indication of anything other than a well nourished cannabis grow. You've also pretty much grown out the canopy to cover the entire grow space. That's good to see—no photon is wasted.

The Uni-T is sufficiently accurate for most growers and, at 826µmol, you're about 200µmol below where I would run the grow.

Re. the accuracy of the Uni-T—it's "calibrated" to 5%± per their literature and I have no reason to not believe that. I tested the Uni-T in 11/23 and here are the results:

View attachment 5469411

I compared the results from the Uni-T against my MQ-500 (calibrated) and determined the "conversion factor" for the light to be 0.0145 which seems to be "about right". "about right" is as close as I could get because I don't have much info on the XS-1500 spectrum but it's got more blue in it than the "average" white LED so 0.0145 is about right.

Is 0.0145 correct? It's close enough. As I see it, the primary goal of measuring PPFD is to get some idea of how much light is falling on the canopy and then let your plants tell you how much light they can use. The most obvious signs of a plant that is getting too much light are that the edges of the leaves will curl inward ("canoeing" or "tacoing") and in some cases leaves will rotate around the petiole in the same way that a Venetian blind opens and closes.

If you're fat 867 now, increase you input wattage by ~10% or lower the light by about 2". That will get you over 900µmol and that's a good number for cannabis.

My practice is to increase light levels in the morning and check the plants at 30 minutes and 60 minutes. If the new light levels are at or above the "light saturation point", the plants will let you know. Cannabis reacts very quickly so two checks, 30 and 60, should do the trick.

In ambient CO2, cannabis will thrive at 1kµmol, assuming that light is the limiting factor. If your grow is in good shape (temp+RH/VPD, adequate nutrient levels, properly watered) you should be able to put that much light on the plant.

The PPFD map for your light is shown here. As expected, the higher the light is above the canopy, the more even the lightcast. In a 3' x 3', there's enough light being generated that you can get ~1k in the center of the grow and still get good light around the edges.

View attachment 5469410

At this point in the grow, your plants have completed most of the "building" process so it's about time to reduce ambient temperatures so that the tops of the buds are <78°. The graphic below is based on the research that Mitch Westmoreland did for his PhD (he was a student under Bruce Bugbee).

He released an excellent video on cannabis about 18 months ago. Check for it on YouTube. It's about an hour long and full of excellent information about getting the most out of a cannabis grow.

View attachment 5469412

So you think i should raise the power of the light? You don't think the lights to close or to strong now? The plants are a lighter green now under the light. I feel like that's going to make the plants even lighter green? Again I'm a newish grower only a couple grows undercmy belt. (Nothing worth smoking)

you personally have the Uni-T meter? Reason I ask is because there's a spot on the PPFD APP where your supposed to pick what light you have, for example "LED 4000k + 10% nm 660...) do you know what I should pick?

Any help is much appreciated

 

[buyyouabeer]

That doesn't look like light issues. You should be thinking nutrients at this stage; your plants are going into some major growth changes. They are going to be needing more N right now or the next thing you will be asking is why are all my leaves turning yellow.

 

[Delps8]

So you think i should raise the power of the light? You don't think the lights to close or to strong now? The plants are a lighter green now under the light. I feel like that's going to make the plants even lighter green? Again I'm a newish grower only a couple grows undercmy belt. (Nothing worth smoking)

you personally have the Uni-T meter? Reason I ask is because there's a spot on the PPFD APP where your supposed to pick what light you have, for example "LED 4000k + 10% nm 660...) do you know what I should pick?

Any help is much appreciated

Per my PM, I don't think this is a lighting issue. Even if the PPFD you're getting from the meter is very low (meaning the your plants are getting a lot more light), I think it's more likely that this is a nutrient issue.

In the PM, the OP has pointed out that the light coloration is found in all three plants and the coloration is light only toward the center. That doesn't show up in the photos here but it could be a function of humans being very good at perceiving shades of green, far better than a camera in a phone.

"do you know what I should pick? "
The conversion factor of 4000+660 is going to be pretty close. What are the options for light type/spectrum?

The graphic below is from the HLG site so choosing the 4000k + 660 is going to get pretty close. And, in reality, it's close enough because the issue is not what the number on the meter is reading. The key point is how the plants are reacting to the light that they're getting.

A meter will get you in the ballpark; the grower has to "adjust fire" after that.




Re needing more N — agree. That could well be the issue and I hope the OP will provide more info about watering and nutrients used. I suspect that's the core of the issue.