Why do you think foliar feeding just before lights out is done?? The stomata remain open for around 20 minutes once the lights go out. Foliar feeding during lights on will burn your plants up but as the stomata is open they will also feed.
Its a chemical reaction so a brain isn’t a requirement for the plant to have bro. When the lights go out the co2 levels drop and the stomata close 
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I don’t foilar feed, not sure why anyone would … So if stomata stay open it slows growth in the plant?
Maybe releases more moisute, but then wouldn’t it take more up from the roots drying them out faster in soil or taking up more nutrients?
Not sure about your argument about foilar feeding …
They release moisture but also take in co2 and other gasses
If the stomata isn’t open they won’t absorb the nutrient.
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And as I stated in the other post, light intensity at the top will be more and they will open, at the bottom of the canopy they will be closed. It will be different across the canopy and plant, they aren’t uniform. It’s not like everyone single one on the plant will either open or close.
And if you read the article you posted, there are many factors to them opening and closing, not just light intensity. They will open and close as they need to, to keep the plant healthy.
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Its a chemical reaction created by the plant during lights on that cause them to open. Its photosynthesis. Also the stomata are mainly located on the under side of a leaf so not in direct sunlight. The upper sides of the leaf is what take in the sunlight.
I’ve tried my best to try and explain. I’m no botanist and I certainly haven’t studied other than a lot of reading
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I’m not doubting your growing capabilities mate. Keeping a plant under 24/0 is fine as long as the humidity is high enough for the plant to thrive as it will loose moisture as the stomata will remain constantly open 
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its normal the plant is getting ready to rest…
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What she said… 
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For almost 30 yrs I’ve grown outdoors at 42 north. Around 16 daylight hrs ( educated guess) daylight or so at the solstice. I never once noticed this drooping at lights out ( sundown). Then I grew outdoors at almost 50 north one summer recently. After struggling with bad water for three weeks I finally awoke to happy plants one morning. Huge relief! Not long afterward I went to check on the plants just before dark. The plants had collapsed. I ran to let my local cousin know our water issues had returned. When we got to the plants he said immediately " they are just tired , they’ve had a long day, they’re fine". sundown 10 something at night and light out at 330 am. About 18 or 19 hrs daylight at solstice. I think he was right. They collapsed near dusk all through june and july. I dont remember if it happened in august and am sure after flowering began it didnt happen. Interesting topic and answers
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grew in southern AZ in a greenhouse… the days where not very long that far south but still some of my plants did this … someone in another thread says the auto flowering plants are sort of famous for it
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For you guys with plants that droop before lights out: what kind of light are you using?
If I give my plants (autos especially) too much light, they don’t droop but the leaves closest to the light yellow out, even with temps in low 70s. Or the serrated edges start to curl up and turn orange. Again, temps are fine and humidity about 50%.
I’m using COBs and having trouble getting them to go more than 25 watts per square foot at 18 inches before seeing light stress… Measuring lux at canopy I can’t get autos over 20k on 18/6 light cycle and can’t get photos over 30k on 12/12 before leaves are affected. 
Under COBs I only every had 1 plant that reacted to too much light by drooping before lights out… Instead the leaves usually start to show symptoms until I dim the light.
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Wow. Thank you all for the many interesting comments. I had no idea this would spark any controversy or this much responce - but I should have known better. This is the internet after all 
I agree with many of you and disagree with some and have no comment on others, but Im too sick to take the time to respond in the detail you ALL deserve.
So for now - thanks for jumping in either way 
Oh - its too soon since I dialed back the lights ON time to tell if there is any change. I will keep you posted.
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There is a limit to the amount of light a plant can process in a 24 hour period, this is commonly understood in plant biology , any photosynthesis beyond 19 hrs is normally so minimal it dosent justify the energy cost.
In my experience some strains do this much more drastically then others I don’t think it’s any thing to worry about unless there are other issues popping up as well your plants are probably just doing there thing.
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not sure if anyone answered …droop is when the leaves look pretty normal but are pointing down instead of being flat out to the side …wilt the leaves them selves look limp
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Used to do 24 all the time really not a bunch of difference except in the e-bill
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Thank you both, now it’s clear, sorry for the off topic in this really interesting thread … 
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This might help. It’s my understanding depending on the plant, hardening off, etc plants can only take in so many moles per day. The software we use at work has a par meter attached and can calculate our daily moles. pretty cool imho.
The daily light integral (DLI) is the number of photosynthetically active photons (photons in the PAR range) accumulated in a square meter over the course of a day. It is a function of photosynthetic light intensity and duration (day length) and is usually expressed as moles of light (mol photons) per square meter (m−2) per day (d−1), or: mol·m−2·d−1.[1][2]
DLI is usually calculated by measuring the photosynthetic photon flux density (PPFD) in μmol·m−2·s−1 (number of photons in the PAR range received in a square meter per second) as it changes throughout the day, and then using that to calculate total estimated number of photons in the PAR range received over a 24-hour period for a specific area. In other words, DLI describes the sum of the per second PPFD measurements during a 24-hour period.[3]
If the photosynthetic light intensity stays the same for the entire 24-hour period, DLI in mol m−2 d−1 can be estimated from the instantaneous PPFD from the following equation: μmol m−2 s−1 multiplied by 86,400 (number of seconds in a day) and divided by 106 (number of μmol in a mol). Thus, 1 μmol m−2 s−1 = 0.0864 mol m−2 d−1 if light intensity stays the same for the entire 24 hour period.
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That is a much better explanation then I can bring myself to type out but that is very good information to be aware of. When. I was taking organic chemistry and micro biology we did alot of similar type studies and that’s when I determined more then 18 hours was really pointless and only raising the electric bill. Plus I’m a firm believer in nature and plants need rest imo.
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Lol, so that’s a copy/paste from Wiki. I don’t write well.
I totally agree with a dark period seeming like a natural thing. It’s been a long while since I did any reading on that, but I could never find a scientific reason why a plant would actually need a dark cycle (other than too many moles per day). If you find anything supporting that please share. 
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