Light Cycles - 24/0 vs 18/6

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Light Cycles - 24/0 vs 18/6

Post by Weedguru Higher » Mon Sep 20, 2010 12:50 pm

Light Cycles - 24/0 vs 18/6

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There has always seemed to be a debate on the vegetative photoperiod. Some growers swear by the 24/0 photoperiod while others feel that the 18/6 photoperiod better suits there plants. Personally, I like to use the 24/0 photoperiod.

The following information is straight from Greg Green's "The Cannabis Grow Bible"


Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorously and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.

Some growers opt to use 18/6 as their photoperiod. This is 18 hours of light, six hours of darkness light regime. Under these conditions the plant will grow quite naturally but not as vigorously as the 24/0 photoperiod.

The 18/6 photoperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves,branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. As we have said already, cannabis is a light demanding plant. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphrodite condition) to 18/6 photoperiod these problems are actually the result of heat stress.

A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained good grow room setup should not require a cooling down period.

24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep that way especially when the plants near maturity (the preflowering stage). An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod unitl your plants are mature enough to express their sex.

Every grower can make a personal choice about light cycle. They can save on their electric bill or prolong ballast/bulb life. 18/6 can be less of a "shock" when changing over to 12/12 for flowering than 24/0 or heat issues can be addressed by fewer hours of light, but basic botany has proven long ago that cannabis needs no dark period.

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Below is a direct quote from Ed Rosenthal who is a marijuana growing guru:

"Marijuana plants photosynthesize as long as they receive light as well as water, air, nutrients and suitable temperature. Photosynthesis is the process in which plants use the energy from light (primarily in the blue and red spectrum's) to combine carbon dioxide (CO2) from the air and water (H2O) to make sugar while releasing oxygen to the air.

Plants use sugars continuously to fuel metabolic processes (living) as well as for tissue building. The plant combines nitrogen ( N ) with the sugar to make amino acids, the building blocks of proteins. They are the substance of plant tissue. When the light is off, the plant's metabolic processes, respiration and growth, continue.

The plant can photosynthesize continuously so it produces the most energy and growth when the light is on, continuously. Continuous light does not stress the plant, which reacts somewhat mechanistically to it.

Plants under an 18-6 light-dark regimen are producing sugar only three quarters of the time. They are thus growing at only 75% of their potential. Leaving the light on continuously will result in bigger plants, faster, which leads to higher yields."

http://www.marijuanapassion.com/forum/s ... otoperiods
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Re: Light Cycles - 24/0 vs 18/6

Post by (weedguru)scarf » Sun Sep 26, 2010 12:48 pm

i had this debate with my friend in china this afternoon on the phone... coincidence :)
he is using 18-6 im using 24
woah

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Re: Light Cycles - 24/0 vs 18/6

Post by SpRi7e » Sun Sep 26, 2010 9:45 pm

what about..

22/2
or
20/4 light cycles?
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Re: Light Cycles - 24/0 vs 18/6

Post by Weedguru Higher » Sun Sep 26, 2010 11:16 pm

Good question...

I haven't found much specific info about those light cycles

Everyone seems to have their own theories and specualtions on light schedules..hard evidence is hard to come by on the matter. No real scientific research study has ever been done about it

Some people even go to 16/8 then 14/10 etc then 12/12 so it mimics outdoor natural light
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