Optimal Light Schedule For Cannabis

Saying that the best light schedule for your cannabis is 12/12 is a myth! Most grow guides claim that you should Give your plants 12 hours light & 12 hours dark each day throughout their flowering cycle. Is that the best light Schedule for all cannabis strains? There are hundreds of cannabis cultivars in the world. These, also known as landraces grow in various regions of the world. These local varieties do not all require the same amount of daily light hours in order to start flowering. Let’s look at what light schedule your cannabis plants will require according to the strain you are growing.

Vegetative Stage

Optimizing Yeilds

To optimize their yields, most growers give their plants a period of vegetative growth. That is because without it, the plants would not be tall or sturdy enough to bear big floral clusters.
You as a grower, determine the length of the vegetative stage by giving your cannabis plants enough hours of daily light so that the plants don’t start flowering.

Reducing The Power Bill

The best light schedule for the vegetative phase is 14 to 18 hours of light per day. Because they come from places close to the equator, tropical Sativas and Pure Sativa Hybrids such as the Original Haze require only about 14 hours of daily light at this stage. However most Indica and hybrid varieties originate from places where the summer days are longer. Therefore, 16 to 18 hours of light per day will be optimal. For vegging weed plants, keep in mind that weed plants need to sleep. However, they can do so even when the lights are on. In other words, giving plants more daylight hours than they need will not harm them but it would be a waste of energy.
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Flowering Stage

As for the vegetative phase, different cannabis strains will require different amounts of daily light hours when flowering.


Indicas/Afghanicas comes from place that are relatively far from the equator. For that reason, they will start flowering even when the daylight hours exceed 12 hours.
The optimal light schedule for most hash plant landraces and Indica dominant hybrids such as OG Kush, Northern Lights or White Rhino is 13/11.
Start the flowering cycle with 13 hours of light per day and gradually reduce it to 11 hours of daily light over the course of about 10 weeks.


Indica/Sativa hybrids such as Skunk#1, White Widow or Jack Herer favor a 12/12 light schedule. It is then possible to decrease the daylight hours to 11 hours per day towards the end of the flowering cycle.


Equatorial/Tropical Sativas come from places where the day length is always close to 12 hours year-round. Therefore, giving these plants shorter days and longer nights with send a strong signal that will help make these long flowering varieties flower a bit faster. For pure Sativas, it is recommended to start the flowering cycle with 11h and 30 minutes of light for 12h and 30 minutes of darkness every day. Then, slowly decrease the daylength to about 10 hours of daily light towards to end of the cycle.
Kullu Sativa

Pure Indian Sativa flowering under 11 hours of daily light.


Ruderalis varieties are day neutral. These come from cold places where the summers are short. In their natural environment, they automatically flower and make seeds during the summer months. After that, the temperatures quickly drop and the plants die. Most autoflowering strains give optimal results with 16 to 18 hours of daily light. Unless you are trying to stress-test your autoflowers on purpose, give them at least 16 hours of light per day throughout their life-cycle.


When growing pure varieties (Landraces), Simply look at the total amount of daylight the plants receive in their natural environment and resort to a light schedule that closely replicates that. Even for most hybrid strains, it is possible to figure out the best light schedule by delving into their genetic makeup (Where their ancestors come from). It is true that the classic 12/12 light schedule works but you can now determine the optimal light schedule for your cannabis strains and achieve even better results!
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9 thoughts on “Optimal Light Schedule For Cannabis”

  1. after reading that plants benefit from light dropped after 6 hours I tried the 6 on 2 off rotating light cycle and it worked very well. I then thought I would try something I had not read about but based on same info I am finishing my grow with 6 on 6 off rotation and the plants are loving it. I believe the results are noticeably better than 18 and six cycle finishing with 12 and 12.

    1. Hi Grant,

      I’ve never heard of a 6/6 light cycle before.
      A whole day (Night+day) is always 24 hours throughout the world.
      Are you vegging your plants using a 6/6 schedule?


      Shan and the Khalifa Team

        1. Hello and thank you Peter.

          If you do 6 on 6 off then 6 on 6 off in a 24 hour period your plants should remain in veg and it may also cause a lot of stress.


          The Khalifa team

  2. In your You Tube Video on Savita’s you recommended a 12/12 Start. Then in one of you comments on that video you said you flip after 7-9 Days of Veg was that Typing error??
    or is that true? Thanks

    1. Hi T shore and thank you for your question.

      You can definitely start all Sativas directly in 12/12 or even 11/13.
      However you can also give them aa few days of veg before you flip them to flower as it can sometimes help slightly reduce their crazy stretch.

      That being said, that doesn’t make a big difference and both methods work very well.


      The Khalifa team

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