Is this light burn?

Week4@inCharge said:

I still don't know what foxtails is ...

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It’s caused by light and heat stress I’ve read, other things can probablies cause it as well. It causes the buds to grow strange sometimes they grow really light and airy not like dense hard buds like what you want and can also make them look deformed.

it is happening to a few on mine now because of the light stress I’m guessing.

this will probablies explain it better

Ok so I’ve took some readings with the lux meter I’ve purchased, I set it at the height of the canopy and turned the lights on full. The reading was around 35,000 lux under lights turned up full around 20 inches away, I think this calculates as around 890 ppfd.

so is the problem light burn or something else? Because from what I’ve read this is within the limits weed can take? But I moved one of the plants that was not effected directly under one of the lights a few days ago and have noticed the tips of the leaves starting to burn like the others and some leaves yellowing??

I have set the lights at 20,000 lux on the meter just to be safe but this has got my head battered, any help or advice would be appreciated.

CARmick93 said:

Ok so I’ve took some readings with the lux meter I’ve purchased, I set it at the height of the canopy and turned the lights on full. The reading was around 35,000 lux under lights turned up full around 20 inches away, I think this calculates as around 890 ppfd.

so is the problem light burn or something else? Because from what I’ve read this is within the limits weed can take? But I moved one of the plants that was not effected directly under one of the lights a few days ago and have noticed the tips of the leaves starting to burn like the others and some leaves yellowing??

I have set the lights at 20,000 lux on the meter just to be safe but this has got my head battered, any help or advice would be appreciated.

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the readings sounds right, as far as I know, and have similar readings the same just like yours carbon copy, run a fan across the top to move the "heat" generated by the lights away from the ladies. Stick your hand in there with the back of it facing the lights, feel the heat? Your plants do too.

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Stick your hand in there with the back of it facing the lights, feel the heat? Your plants do too.

That's advice I've seen for HID lighting but not with LED. I've read that LED doesn't have the IR heat like HID; that's why you can run LED air temps in the 80's but weed like temps in the 70's with HID lighting.

Stick your hand in there with the back of it facing the lights, feel the heat? Your plants do too.

That's advice I've seen for HID lighting but not with LED. I've read that LED doesn't have the IR heat like HID; that's why you can run LED air temps in the 80's but weed like temps in the 70's with HID lighting.
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Sounds good, yet more than half of these threads have burnt leaves from led lighting.. or is Google messing with me. No IR that I know of either, could you run IR all day? Saw it only recommended for couple hours a day, I don't know.

I think it's light burn too.

I grow under a 1000w HPS and somewhere around week four - six my plants look like yours. I grow in soil so by the time I react the plants are pretty much goners. I'm trying to decide if I should buy a 400W or 600W HPS or even LED. I've got the fixtures for HPS so 400W would be cheapest.

Good luck!

CARmick93 said:

Thanks for the reply, I’ve only been doing this for about a year now so still got a lot to learn, I never even thought about testing the lights before as they could damage the plants this much. I’ve ordered a lux meter so hopefully can get them set up right.

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If you can swing the $$, get a PAR meter. You can get one for <$200 and it lets you set your light level. Lux meters are a WAG unless you get info from the company that made your light that will remove the "extra" light that the lux meter is reading. Even then, I'd go with a meter that measures light that plants use instead of using a meter that measures light that humans use.

I don't try to save money on condoms, parachutes, radar detectors, or light meters.

Look at all the commercial grows you see here as advertising.Led lights are up quite high.

Week4@inCharge said:

Stick your hand in there with the back of it facing the lights, feel the heat? Your plants do too.

That's advice I've seen for HID lighting but not with LED. I've read that LED doesn't have the IR heat like HID; that's why you can run LED air temps in the 80's but weed like temps in the 70's with HID lighting.

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Sounds good, yet more than half of these threads have burnt leaves from led lighting.. or is Google messing with me. No IR that I know of either, could you run IR all day? Saw it only recommended for couple hours a day, I don't know.
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That's correct. LED generate very little/no IR. Besides that, most of our senses are awful when it comes to accuracy (that's why we have binoculars, thermometers, weighing scales, etc.). The key metric is leaf surface temperature which is usually a within a few degrees ± of air temp. Get a cheap IR thermometer gun and crank the heat up to 86/30.
The attachment is from research done at U MISS (Google "chandra cannabis research"). With a PPFD of 500 µm (shorthand for nano moles of light per square meter per second. Light is photons - particles - and it's measured in "moles". A mole is a short word for a "shit ton", BTW. A nano mole is a billionth of a mole. That's are that sensitive and that's why a PAR meter costs.) you get about 14 µm of photosynthesis at 77°. Bump the temp to 86° and you get around 18 µm. That's almost 30% more photosynthesis. Bump the PPFD to 700 and things look even better.

myke said:

Look at all the commercial grows you see here as advertising.Led lights are up quite high.

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The only reason that I can think of to move a dimmable light away from the canopy gets you less light but a more uniform distribution of light. But I'm a personal grower not a commercial grower. Light falling on a canopy is more uniform at, say 24" vs 6". Check out the lights at ppfdcharts.com. That appears to be real data.
The power of light falls off the further you move from it (duh) but it's amazing how much it falls off by moving from 6" to 12" for example. Check out the inverse square law.
Just for grins and giggles, I've attached the PPFD map from the Kind LED that I used in 2017 (Series 1) and from their Series 2 light. When I unarchived my grow equipment at the beginning of this year, I contacted Kind and they sent me those two documents. Both of those are for a 2' x 4' tent. In my opinion those fall into the "dogshit" category. When I got those documents, I put the Kind in the box and put the box in the trash and started shopping for a light I ended up with a Mars SP 3000 and have now gone to a Growcrraft X3 (the Growcraft lights are on sale at the moment). Those light are in the "not dogshit" category.

Week4@inCharge said:

the readings sounds right, as far as I know, and have similar readings the same just like yours carbon copy, run a fan across the top to move the "heat" generated by the lights away from the ladies. Stick your hand in there with the back of it facing the lights, feel the heat? Your plants do too.

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Thanks, I’ve just set up a wall mounted oscillating fan, I had one in the corner but wasn’t really blowing across the tops.

Even with the LEDs all the way up there isn’t really much heat when you put your hand underneath even when close, but I’ve turned them down a bit now anyways just hope this doesn’t happen again on the next grow.

What would be the (sweet spot) for watts output to get 800 or so PpFd at say 28 inches away? does it vary by manufacturer?

CARmick93 said:

Thanks, I’ve just set up a wall mounted oscillating fan, I had one in the corner but wasn’t really blowing across the tops.

Even with the LEDs all the way up there isn’t really much heat when you put your hand underneath even when close, but I’ve turned them down a bit now anyways just hope this doesn’t happen again on the next grow.

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Flowers take up a lot of nutes and when they can't find enough they rob them from the leaves, it's why when we're in veg you don't see any problems using the same lighting, I think it's the potash (potassium) that strengthens leaves against the intense lighting. Isn't it odd that 12 hour lighting does more damage than 18 hour veg lighting..lmfao.. so weird. That's one advantage of outdoor grow.. super bright lighting and gentle cool breeze... makes for opti,mum growing.

This is burn from led light within the last 24 hrs.

Three Berries said:

This is burn from led light within the last 24 hrs.

View attachment 5001509View attachment 5001516

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they look a little thirsty. how close are your lights?

Below is a pic of an indoor Dutch greenhouse using LEDs. The crop is premium strawberries.

If ya ask me the lights look to be 20 feet above the plants.



Below is a pic of an indoor Dutch marijuana grow using HPS. To me the lights look like they're about eight feet above the canopy.

I had two 1000w HPSs about 24 inches above my plants in a 10'x5' tent. I think I'm doing it wrong.

rmax said:

Below is a pic of an indoor Dutch greenhouse using LEDs. The crop is premium strawberries.

If ya ask me the lights look to be 20 feet above the plants.

View attachment 5001547

Below is a pic of an indoor Dutch marijuana grow using HPS. To me the lights look like they're about eight feet above the canopy.

I had two 1000w HPSs about 24 inches above my plants in a 10'x5' tent. I think I'm doing it wrong.

View attachment 5001550

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There has to be a happy medium to this equation.

Week4@inCharge said:

There has to be a happy medium to this equation.

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The elusive unicorn strain.

rmax said:

Below is a pic of an indoor Dutch greenhouse using LEDs. The crop is premium strawberries.

If ya ask me the lights look to be 20 feet above the plants.

View attachment 5001547

Below is a pic of an indoor Dutch marijuana grow using HPS. To me the lights look like they're about eight feet above the canopy.

I had two 1000w HPSs about 24 inches above my plants in a 10'x5' tent. I think I'm doing it wrong.

View attachment 5001550

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I think you're right on both counts.
And that doesn't refute my assertion.

When I wrote the opening sentence, I went back and add "dimmable". The mental model I was working from was contemporary, dimmable, LED's. And the unstated assumption which I should have stated, is the the lights were movable. The LED's in the pix are blurples so I know that they're at least a few years old. I can't state it as a fact but I suspect that blurples were not dimmable. I bought my Kind in 2017 which means it was designed in 2016± - I don't know what commercial lights were light in 2017 but I don't recall bluples for the small/personal grower being dimmable. The other issue is being movable. They don't appear to be and, given that they're well away from the canopy, I'd infer that they're not. And the reason I infer that is because of the inverse square law. The if you double the distance between a light source and the destination, the amount of photons drops to 25%. That's considered a "law" of physics and it applies to light, regardless of the source.

One factor in…life is tradeoffs. The engineers who designed that facility must have weighed the cost of the additional electricity required to keep the lights at that height vs the cost of building a system that was movable. Of course, I can't say that the people who designed that system did that but that process is inherent in pretty much any decision making process.

Looking at the filament lights, you've got similar constraints and similar tradeoffs. Unlike LED's, incandescent lights give off a lot of heat so HVAC load goes up. And, like the LED's, those lights don't appear to me movable. I'll admit I don't know if incandescents for cannabis are dimmable - I've got HID's on my motorcycle and they're not dimmable but, again, they're an older design so, on that point, don't know.

Dollars to doughnuts, new designs don't use blurples and, if possible, lights are movable. In addition to having better LED's, we've got skyrocketing power costs, especially in Europe with their fixation on intermittent energy. The cost be KW hour is brutal over there, even worse than California. Those costs were probably not anticipated when these buildings were being designed - neither, apparently, was the mayhem that's going on right now in Europe being acknowledged just a few months ago. So new design will incorporate the technologies on a cost efficient basis - incandescent lights are no longer cost efficient and having lights 20' from the canopy is brutally expensive and quite likely to continue to get worse.

Week4@inCharge said:

There has to be a happy medium to this equation.

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The equation being how commercial growers design their facility. Of course there is! But what the happy medium consists of varies. Some growers may have a blank check and not expect to be profitable for many years or, perhaps, never (I know a grower in that situation). Others have scraped up enough $$ to get started, just barely, so they can't afford the "bells and whistles". Again, it's all tradeoffs.

For all growers buying lights, for all products really, the big tradeoffs are features vs price - it you've only got $150, for example, the feature set is pretty limited. Once you start going up in price you can add features - removable driver, waterproof, chainable, dimmable, foldable, connection to a central monitoring system, variable spectrum. The list gets longer all the time, as technology improves and allows features to trickle down from the lab to the high end and then down the price chain.

But there's more to it than making the light run. The grower has to learn how to make it work. The instructions of "30" above canopy for seedlings" is a good guideline but not optimal, especially since light output from a given fixture drops over time and especially since the manufacturer is not on the hook for the outcome of a grow. I put some $$ into a PAR meter - why trust my crop to a manufacturer guideline? They have far lest vested interest in the success of my crop than I do so I stack the deck in my favor to come up with a successful grow.

And that's one of my hobby horses - light is food for a plant (nutes are analogous to vitamins and minerals). It's easy to overfeed or underfeed a plant, as we've seen. Unfortunately, without a way to measure how much food it's getting you have to rely on experience (experience is very expensive) or wait until the plants show symptoms. In the worst case, the plants suffers tissue death. At the moment, the cheapest PAR meter is just under $200 but some of the reviews are, not unexpectedly, not positive. But the reason that it's a $200 product is because it's not made like a $500 product (tradeoffs anyone?) but, as far as I can tell, it's better than a software solution (I tested Corona/Photone and decided against using it) and using a light meter seems appears to have too big of a margin of error.

My approach is to use the technology that is cost effective for me, keep learning, and, though I didn't get it at first, listen to your plants.

Week4@inCharge said:

What would be the (sweet spot) for watts output to get 800 or so PpFd at say 28 inches away? does it vary by manufacturer?

Flowers take up a lot of nutes and when they can't find enough they rob them from the leaves, it's why when we're in veg you don't see any problems using the same lighting, I think it's the potash (potassium) that strengthens leaves against the intense lighting. Isn't it odd that 12 hour lighting does more damage than 18 hour veg lighting..lmfao.. so weird. That's one advantage of outdoor grow.. super bright lighting and gentle cool breeze... makes for opti,mum growing.

Click to expand...

PPFD varies by the model of the light, the age of the light, the height of the light above the canopy (which varies according to how even the canopy is), and where the light is falling within the "spread" of the light. On the latter point, check out ppfdcharts.com or, for an extreme example, the PPFD chart that I posted that Kind sent me. There's lots of variables but only one way to measure it (a light meter), one way to measure it with some level of accuracy (Photone or a cheap PAR meter), or to a high degree of accuracy (an Apogee or a LI-COR which are accurate to something like 1%± of international standards).

Looking down the road a bit, my hunch is that software on a smart phone will get better and will be a good solution for a lot of growers. I write software so I'm biased to some extent but my thinking is that, as phone sensors get better, products like Photone will be able to tease out better data more consistently. That's just part of how technology has evolved (I've been writing software for > 30 years). OTOH, there will still be the trade offs of trying to wring highly accurate data out of a cheap phone camera sensor that's designed to capture a different spectrum vs using a purpose built product. The good news is that those differences are reflected in price.