Best Light Schedule for Autoflowers

by in Cannabis Growth February 27, 2018

What is a light cycle and which one is the best for your auto-flowering plants?

Unlike photoperiods that need at least 12hrs of darkness to trigger flowering, autoflowers automatically are in the flowering cycle from the seedling stage. They start producing buds based on age thus they don’t depend on darkness to start the flowering cycle.

Tip: Light cycles are used to simulate seasons in nature, more light = summer, more darkness = winter.

1. What is the best light cycle for autoflowers?

Most growers agree that the optimum amount of light to give auto-flowering strains is somewhere between 18-24 hours of light a day. As a grower you should adjust the light depending on the cultivar youre growing.

There are basically three life cycles aka Light schedules: 24/0, 18/6, and 12/12 (the first number is hours of light, the second is hours of dark). You can always adjust the cycle as long as they are receiving more than 12 hours of light a day (to achieve the best results). An example would be 19/5, 16/8, 22/2, etc.

Having that in mind, there are growers experimenting with schedules like 6/18 but if youre new to growing you should stick to the basic schedules mentioned above.

2. Do autoflowers need darkness?   

There are growers who believe auto-flowering plants need a dark period and wont be as healthy if they get a 24/0 light schedule. Theres no real evidence of that but there may be exceptions. Also have in mind that a 24/0 will lower humidity, increase temperature, and increase the light bill.

Schedules like 18/6 or 12/12 will save you electricity and if the few hours of darkness indeed help the plant to grow better, its a win-win. We recommend starting with an 18/6 light cycle and if you see your autoflower has the potential to grow more, you can always try again in the next cycle.

3. 24/0 Light Cycle

Plants usually grow faster when they get more light. This schedule is a good choice if you live in a cold climate, keeping the lights turned on 24hrs a day will keep your plants warm.

24/0 Light Cycle for cannabis plants

24/0 Light Cycle for cannabis plants.

Obviously, this is the easiest light cycle as you dont even need a timer, just turn on lights until harvest.


•  Doesnt require a timer. 

•  May result in the best yields.


•  Uses more energy, can get expensive.

4. 18/6 Light Cycle

This is the most common cycle for autoflowers. You’re providing enough light for your plants to develop and a few hours of dark for them to rest, encouraging healthy growth. This can be good in hot climates.

You can leave your lights at night and have them turn off during the 6 hottest hours of the day. By using this schedule youll be using around 25% less electricity, which adds up to be a good economy at the end of every harvest.

18/6 Light Cycle for cannabis plants

18/6 Light Cycle for cannabis plants.

A lot of growers who have experimented with 24/0 and 18/6 light cycles say they didnt notice any major difference in final yield. The only minor inconvenience with this schedule is having to buy and adjust a timer. They cost around 10 bucks so it shouldnt be a problem at all.


•  Allows your plants to rest.

•  Uses less electricity, allowing us to save on electricity.

•  Can help lower temperatures and increasing humidity in hot climates.


•  Requires a timer. This shouldnt be a problem at all, as this is the first thing you should buy when growing indoors.

5. 12/12  light cycle

The 12/12 schedule is normally used for photoperiods. It can also be used for autoflowers but its not that popular. Normally growers give autoflowers this light cycle when they have them growing in the same tent as photoperiods. By giving your autos 12/12 youre not using them to their full advantage.

12/12 Light Cycle for cannabis plants

12/12 Light Cycle for cannabis plants.

Because your plant is getting less light each day, it isnt able to make as much energy to promote growth. It will underperform compared to the other light cycles, that being said, you can grow them just fine if you dont mind reduced yields and an overall smaller plant. 

6. In Conclusion

There isnt really a proven best light cycle. Before going for any light cycle, think about electricity costs and the climate youll be growing in. If you are in doubt, start with 18/6. This cycle is the most used and should work for all autoflowers.

When growing outdoors you have to work with what you have as you cant control the sun (obviously). Outdoor growers should be aware that with the change of seasons the amount of daylight may increase or decrease but autoflowers should grow fine in all seasons. 

Quoted from By Enzo Schlacci

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