Is this a sign of light burn and too low??!

Please examine these close ups of the top of a plant. This is the tallest of them and I noticed this twisting and slight whitening of the very top center of one plant. When I measured distance from light to this top, I got 20”. I raised it two more inches to 22” to try and compensate and added a trellice. Almost 2 feet over them seems high to me but the led light is powerful. It is an AC Infinity EVO 4 3X3 full spectrum light. I have the intensity set for 50% although it suggests 80% for vegging at this point. Erring on the side of caution. Although I could maybe raise up to 2ft and bump it up to 60%? I feel this may be a sign they are not quite ready to handle much more light now. Thoughts?

Smokenpassout said:

Please examine these close ups of the top of a plant. This is the tallest of them and I noticed this twisting and slight whitening of the very top center of one plant. When I measured distance from light to this top, I got 20”. I raised it two more inches to 22” to try and compensate and added a trellice. Almost 2 feet over them seems high to me but the led light is powerful. It is an AC Infinity EVO 4 3X3 full spectrum light. I have the intensity set for 50% although it suggests 80% for vegging at this point. Erring on the side of caution. Although I could maybe raise up to 2ft and bump it up to 60%? I feel this may be a sign they are not quite ready to handle much more light now. Thoughts?

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Not seeing anything that looks like too much light but it's hard to say from the pictures. When posting photos, it's helpful to show a picture of the entire grow environment as well as a large portion of the plant. Closeups can be helpful step back a bit.

Re the EVO 4 - can you send the link for recommendations for hang height and dimmer settings? I haven't been able to find anything definitive on their site.

AC Infinity publishes a PPFD map but not for 24". The PPFD map, below, shows ~1350 at 18". Conventional wisdom is to give cannabis 300-600µmol in veg. If you're shooting for average, that's 450µmol so a dimmer setting of 35% would get you in the ballpark.

My hunch is that, at 24", that light is generating a PPFD of about 900-1000µmol so 50% would be just about OK.

Also, how many days above ground?

Delps8 said:

Not seeing anything that looks like too much light but it's hard to say from the pictures. When posting photos, it's helpful to show a picture of the entire grow environment as well as a large portion of the plant. Closeups can be helpful step back a bit.

Re the AVO 4 - can you send the link for recommendations for hang height and dimmer settings? I haven't been able to find anything definitive on their site.

AC Infinity publishes a PPFD map but not for 24". The PPFD map, below, shows ~1350 at 18". Conventional wisdom is to give cannabis 300-600µmol in veg. If you're shooting for average, that's 450µmol so a dimmer setting of 35% would get you in the ballpark.

My hunch is that, at 24", that light is generating a PPFD of about 900-1000µmol so 50% would be just about OK.

Also, how many days above ground?


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I’m at 38 days. Here’s the only pic I’ve been able to find about light placement.

Smokenpassout said:

I’m at 38 days. Here’s the only pic I’ve been able to find about light placement.

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Thanks for posting that. Is that from the manual?

A grower could run that light with those settings but you would have to pay close attention to the plants because that's extremely aggressive in terms of giving your plant a lot of light.

What I don't see is any signs of light avoidance but that's because I don't have a sense of what the plant(s) or the grow looks like. Per above, the pictures are such close ups that I can't really see the shape of the leaves, the location of the leaves in relationship to the light, etc.

Given that it's been another few hours since the original posting, if it was a light issue, it would have gotten worse. Cannabis reacts quickly to significant amounts of excess light. I routinely give my plants too much light but I run them very close to the light saturation point. When I exceed that, the leaves curl within 15-30 minutes.

I do notice that the ends of some of the leaves are very linear. They seem to have been cut at the ends.

Based on the hang height and dimmer % as well as the color of the leaves, the leaves appear healthy so the PPFD that they're getting should not be an issue.

Again, not knowing anything about the grow itself, that could be completely wrong. I've seen plants in veg that can't tolerate 500µmol and, after many back and forth questions, the plant really was at 500 and the reason it couldn't tolerate any more than that was because poor watering practices had resulted in the soil being hygrophobic.