The Importance of Dark Cycles (Calvin-Benson-Bassham cycle)

[J.James]

Some growers opt to keep their cannabis plants under 24 hours of light in aims to maximize growth during the vegging stage. Most growers, however, veg their cannabis plants on an 18 light/6 hours dark light cycle. Between these two options, it is recommended that growers veg their cannabis plants on the 18/6 light cycle in order to provide a dark period, which will allow cannabis plants to complete the photosynthesis cycle.

Photosynthesis is the process by which plants convert light energy and carbon dioxide into plant food (glucose/carbohydrates) and oxygen. Cannabis plants require three resources for photosynthesis: light, carbon dioxide, and water. During the light cycle, light reactions use light to produce both ATP and NADPH (an electron carrier) in the chloroplast thylakoids. These products are then stored in the chloroplast stroma, where they are then used by the “dark cycle,” the second part of photosynthesis that absorb carbon dioxide. This dark reaction is scientifically known as the Calvin-Benson-Bassham cycle, and is independent of light energy; it completes photosynthesis by absorbing carbon dioxide to complete the synthesis of carbohydrates.

Any questions?

 

[sfrigon1]

Some growers opt to keep their cannabis plants under 24 hours of light in aims to maximize growth during the vegging stage. Most growers, however, veg their cannabis plants on an 18 light/6 hours dark light cycle. Between these two options, it is recommended that growers veg their cannabis plants on the 18/6 light cycle in order to provide a dark period, which will allow cannabis plants to complete the photosynthesis cycle.

Photosynthesis is the process by which plants convert light energy and carbon dioxide into plant food (glucose/carbohydrates) and oxygen. Cannabis plants require three resources for photosynthesis: light, carbon dioxide, and water. During the light cycle, light reactions use light to produce both ATP and NADPH (an electron carrier) in the chloroplast thylakoids. These products are then stored in the chloroplast stroma, where they are then used by the “dark cycle,” the second part of photosynthesis that absorb carbon dioxide. This dark reaction is scientifically known as the Calvin-Benson-Bassham cycle, and is independent of light energy; it completes photosynthesis by absorbing carbon dioxide to complete the synthesis of carbohydrates.

Any questions?

Why 18 and 6 though ? Why not 22 and 2 . U have peaked my interest

 

[J.James]

Good Question, the process doesn't start until a reduction of NADP, which comes from a light-dependent reaction. So the process doesn't start as soon as the lights go out, but when the plant has rested for pierid of time without light. After the plant has rested it will have to process all the stored "Food".

More Light = More to process = More time to complete.

One study states that for every 6 hours of light the plant will need 2 hours of dark to process the carbs. So in theory you could run a 6 and 2 veg cycle for increased growth.

Did this answer your question?

 

[TheSadVeryBadMadGrower]

I have ran plants on 18/6, 20/4 and 24/0. The real only difference I seen between the plants was a lower electricity bill. But I did not do this with clones from the same plant so technically it could be an invalid assumption

 

[sfrigon1]

Good Question, the process doesn't start until a reduction of NADP, which comes from a light-dependent reaction. So the process doesn't start as soon as the lights go out, but when the plant has rested for pierid of time without light. After the plant has rested it will have to process all the stored "Food".

More Light = More to process = More time to complete.

One study states that for every 6 hours of light the plant will need 2 hours of dark to process the carbs. So in theory you could run a 6 and 2 veg cycle for increased growth.

Did this answer your question?

Absolutely ty

 

[Hotwired]

There was a scientific study showing that cannabis plants gain very little in growth when using more than 16 straight hours of light indoors. I use 16 to save $$. Plus, I only give them 12 hours of full light and 2 hours each before main light on and off. They love it. Never seen fuller roots in my pots in a shorter amount of time. It was an experiment that worked out very well imo.

 

[H.A.F.]

Is there a timer that can brighten/dim the lights?

What if at lights on they were at the lowest intensity, then over the next few hours they ramped up to whatever maximum you set? Then a few hours before lights out they started dimming back to off?

More like what they would get outside.

 

[Hotwired]

Is there a timer that can brighten/dim the lights?

What if at lights on they were at the lowest intensity, then over the next few hours they ramped up to whatever maximum you set? Then a few hours before lights out they started dimming back to off?

More like what they would get outside.

I have my main light in an air cooled reflector @ 600 watts on its own timer and two 2 foot T5 HO 24 watt bulbs on either side of the reflector on its own timer as well.

I run the T5's from 4 am to 6:05 am and from 5:55 pm to 8 pm. They light up the whole 4 x 4 tent amazingly bright for 48 watts. The main 600 watt light runs from 6 am to 6 pm. I run two veg tents in one room on a 15 amp circuit easily by using this method. The main 600 watt lights only overlap by 30 seconds or so.

The whole room and tents run 7 total fans 24/7 so this raises total watt usage a bit.

A few pics @ 25 days veg:

 

[baldmountain]

Any questions?

First, you need to write a book. You post facts with scientific rationale to back it up. It would be nice to have all this collected in one place.

Why 18/6 and 12/12 vs. some other cycle? I've been trying 17/7veg and 11/13 flower and it seems okay. (I don't have enough growing experience to compare. And I wired the socket my timer was plugged into wrong so it never turned the lights off properly on my first grow. They are much better now that I wired the socket properly. )

 

[Artisan_tek]

run my girls 24/7 in the seedling stage and in veg. when i first started growing i would 18/6 them up until flower

Never noticed any difference except for the girls under 24/7 light seem to grow faster, use up more nutes and the electric bill is a little higher but with leds it doesnt factor out to be much

 

[Hotwired]

run my girls 24/7 in the seedling stage and in veg. when i first started growing i would 18/6 them up until flower

Never noticed any difference except for the girls under 24/7 light seem to grow faster, use up more nutes and the electric bill is a little higher but with leds it doesnt factor out to be much

Electric is a big factor for me. I like to save wherever I can. My A/C stays on all year so I have to be frugal.

 

[H.A.F.]

Electric is a big factor for me. I like to save wherever I can. My A/C stays on all year so I have to be frugal.

Electric here is cheap. I don't see the point in 24/0 because why?

Unless you are trying to match your light cycle to the above the Arctic circle where they are really known for their weed 18/6 doesn't really seem right either.

So for me, the 18/6 part is actually the most stress I want to put on a plant. Stress - meaning not like outside. And I have been dialing back the lumens or the light height instead of maxing everything out there as well.

I think (bro-science-alert) that the closer to the edge that you run things, the more likely you are to have issues. And then to have those issues compound rapidly and make you start posting new threads on forums and asking uncomfortable questions

 

[sfrigon1]

I vegged 22 and 2 for years and I noticed shorter stockier growth, which w certain strains actually helped in flower .

 

[H.A.F.]

shorter stockier growth

*stunted*

 

[sfrigon1]

*stunted*

Stronger

 

[Artisan_tek]

Electric here is cheap. I don't see the point in 24/0 because why?

This is how I feel about 18/6. Electrics cheap here plus leds cut the cost down even more so if I can get faster growth running them 24/7 why not.

Another factor for me. Not so much anymore but before I use to veg my plants in the same room I had my flowering tent in. I couldn’t keep that room light tight. Honestly not sure if that causes hermies or not but I figured if I was going to go 18/6 I didn’t want any light leaks. So with the setup I was using it just made more sense. After I started noticing the little changes Ive always done it that way.

If I was running a bigger op u better believe they’d be on 18/6

 

[Hust17]

I couldn’t tell the difference between 18/6, 20/4, and 24/0. But i don’t have a lot of experience
I’m at 24/0 for babies and 18/6 once they are not seedlings anymore.

 

[H.A.F.]

so if I can get faster growth running them 24/7 why not.

See the original post. Incomplete photosynthesis.

 

[H.A.F.]

I figure that if all these breeders have produced all these fine genetics, why should I beat the shit out of them with constant light? Let the plants do what they do.

 

[Artisan_tek]

I couldn’t tell the difference between 18/6, 20/4, and 24/0. But i don’t have a lot of experience
I’m at 24/0 for babies and 18/6 once they are not seedlings anymore.

Ime it’s not a big difference. I use to run everything 18/6. To each their own