24 hr. lighting versus 18 hr. lighting

Can anyone share their knowledge on 24 hr. lighting vs. 18 hr. lighting? Why do some say it's better to have a period of darkness and why do some say 24 hrs. of light is better. Can anyone back their wisdom with scientific fact?

24hr light cycle: will cause taller plant on the whole as more light is available
18hr cycle: causes stockier plant

I prefer 18hrs from a week old 24hrs from seed till then.

misanthropeaic said:

Can anyone share their knowledge on 24 hr. lighting vs. 18 hr. lighting? Why do some say it's better to have a period of darkness and why do some say 24 hrs. of light is better. Can anyone back their wisdom with scientific fact?

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I've tried it both ways and it's not that much of a big deal however you do it so now I start off 24 and work my way to 18 I think people like 18 more because it's more like outside

im running a 24 right now and almost want to switch to 18-6 just to save that extra dollar on the power bill.

18hrs is the best option in my opinion because I believe plants need to rest and an 18hr cycle has always worked very well for me and many others. I dont need my plants to grow any taller than they do already so I say ''if it aint broke then dont fix it'' lol. I use HPS lights so I have no experience with using others like fluros etc so there may be a difference when growing under them but I would never put my plants on 24hrs under my 600 watt HPS.

sirus420 said:

im running a 24 right now and almost want to switch to 18-6 just to save that extra dollar on the power bill.

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Ahh yes the power bill, I forgot about that aswell. When using high wattage HPS lights it would add more $$$ to the power bill which I dont want.

well my bigger one is 6 weeks and the other is like 3, would it hurt them to change it to 18/6?

i have had my plants under my 400 watt hps and surrounded by 3 100 watt hps lamps for side light. i leave them under there for 24 hours a day. they been under it for months with no break. now that i have seen the growth, last night i decided to give the 18 hours a go. one benefit i can see coming is a little break on my electric bill. id really like to put one in 24 hours and one in 18 hours light and video tape the difference. one thing i didnt do last time that im deffinitly doing this time is keeping a journal on feeding. i started my first clones ever today, and im wondering if i need to gie them a dark period....anyone? 24 hours light for a clone or do they need a break. as far as i can tell all the dark does is cause them to stretch and grow taller...i lst and suppercropp to keep mine short and bushy anyway.

Cannabis is a c3 plant, meaning it does not need a period of rest at night. There was a study (ill try to find it) that compared 18/6, 20/4, and 24/0. there was not much of a difference in the 24/0 and the 18/6, the one that did slightly better was the 20/4.

I dont think it will hurt them but dont take my word for it because I have never done it before lol. You could slowly cut back the hours but I would just change it to an 18hr cycle and see how they go, just keep a close eye on them.

What do others think?

If the study suggests theres not much difference between them then why bother using a 24hr cycle?

Thanks dude. That is exactly the response i was looking for. I would appreciate it if you could point me in the direction of those studies. Thank You

Exactly, if studies show then there is no need for 24. However he said a study shows that out of all 24, 18/6 and 20/4 faired better. I would still like to know where those studies could be found.

misanthropeaic said:

Exactly, if studies show then there is no need for 24. However he said a study shows that out of all 24, 18/6 and 20/4 faired better. I would still like to know where those studies could be found.

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Im looking hard.....

Your hard work is greatly appreciated.

Im really having trouble, i KNOW i read this somewhere...
Here is a bit of anecdotal evidence: https://www.rollitup.org/indoor-growing/118897-veg-stage-lights-18-6-a.html

Also Ed Rosenthal Seems to think that seedling will grow 33% faster in 24/0 than 18/6... So im not gonna go by his opinion, thats too big of a difference to be logical.

Thats like saying todays pot is 25% thc..... really... trichromes are the only thing that contain thc and thats not even close to a quarter of the plants dry weight.

Im going to assume this... currently we just dont have the scientific information to back up any of these claims, only anecdotal evidence.

Now cannabis is a c3 plant so it does not NEED a dark period. For sugar production that is. However how many other process are there tha we dont know about that go on at night. Saying that i would only assume that something between 18/6 and 24/0 would be best.

Also at night plants arnt absorbing energy so they put all effort into growing up and out. During the day they process and collect energy. So a brief night period would seem to give them a little boost.

Thanks for the effort. Even though you couldn't find the studies, i still found your information and logic to be quite helpful. I'm sure i will come across those studies myself sometime. Once again thank you for your time and effort.

lampshade said:

Cannabis is a c3 plant, meaning it does not need a period of rest at night. There was a study (ill try to find it) that compared 18/6, 20/4, and 24/0. there was not much of a difference in the 24/0 and the 18/6, the one that did slightly better was the 20/4.

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Yes ive found 20/4 to be the best

Your very welcome, i just want to help. If i come across them myself i will pm them to you. But im still gonna go with my gut and say 20/4 is my personal best. Lamp.