You’ve decided to try out growing autoflowers, and need a bit more information on what specific lighting they require. Or possibly you’ve already tried experimenting with these wonderful strains, and need a refresher to start making progress again.

Whatever your reason, rest assured you’ve found the right guide, and we’re here to lend a helping hand. Today we plan to cover all types of lighting, lighting cycles, and necessities that best suit your strain and cultivar. We want to make sure your plant grows healthy and is ready to harvest in no time!

Are there lights that are better for autoflowers?

When it comes to autoflowers generally there isn’t a “best light” for these specific strains. We discussed in previous guides how resilient these guys are. And if you so desire, you’re fully capable of growing them with only sunlight and on whichever lighting cycle you choose.
Maybe you have experience with photoperiod cannabis and their sometimes strict regimens. It may not be too far of a stretch to consider providing your autoflower with the specific spectrum it needs during each growth stage.
When a diurnal plant is in the vegetative stage, growers typically use blue lights (400 to 550nm). And when it enters the flowering stage growers will transition it to reddish-yellow lights (550 to 700nm).
It is perfectly acceptable to apply the same lighting techniques used on photoperiod strains, with autoflowering strains.
The benefit of providing a blue light during the vegetative period is that it aids in their growth. This process helps produce a shorter and stocky healthy plant. During the flowering stage offering your plant the reddish-yellow lights, promotes budding and results in larger more dense flowers.


Which light cycle is best for autoflowers?

When it comes to autoflowers the consensus with most growers is that the optimum lighting range is between 18 to 24 hours. Light cycles are determined by hours of light versus darkness. An example would look like: 18 hours of light and 6 hours of darkness (18/6).
With autoflowering plants, there are four basic lighting schedules routinely used by most growers depending on their cultivar:

  • 24/0
  • 20/4
  • 18/6
  • 12/12

We will go more in-depth about these lighting cycles and the benefits each provides. But keep in mind that though these are the more common cycles, what works best for your plants may differ.
Feel free to choose or adjust a lighting schedule at your discretion. Remember though, if you decide to adjust from one cycle to another, be sure to do it gradually. You don’t want to overly stress your plant or plants. So long as your autoflowers are receiving 12 hours at minimum, you’re sure to receive the best results.

Do autoflowers require darkness?

Before we dive into the types of light schedules there is one topic we would like to discuss. In some of our other guides, we talked about how autoflower strains are a derivative from the strain ruderalis.
However, they were bred with either a sativa or an indica, making them stronger than their ruderalis lineage. And due to their genetic makeup, autoflowers do not rely on darkness to flower. So some growers believe a 24/0 cycle works just fine.
In contrast, other growers claim that not providing a dark period will decrease the plants’ overall health. This in turn can lead to shorter plants and lessen their overall harvest.


Types of lighting cycles

Now we know a bit more about the types of lighting best suited for our autoflower friends. Likewise, we learned the potential impact the amount of darkness you provide them with makes.
Next up we have the 4 basic light schedules that growers recommend for autoflowering strains.


24/0 lighting cycle

If you will be growing your autos in a colder climate, a 24/0 lighting schedule is recommended. This means you will be leaving your HPS or LED lights on 24/7. Which, in turn, keeps your plants warm and removes the need for a timer.
Typically, the more light a plant is exposed to the faster it grows. So this process allows your plant to develop quicker and diminishes the time spent regulating the light cycle. Since you will be keeping your lights on until its harvest time.
With that in mind, this particular light cycle can tend to be a bit more pricey. This is why it is suggested for growers who use it out of necessity.


  • No need for a timer
  • Potential for higher yields


  • Can be expensive due to higher electricity usage

20/4 lighting cycle

Quickly becoming the more favorable amongst autoflower growers is the 20/4 lighting cycle. This is because it offers a medium between the 18/6 cycle and the 24/0 cycle.
What makes this lighting schedule ideal is while you’re not spending as much on electricity as you would with a 24/0 cycle. You are also providing your plants with some rest they wouldn’t receive on a 24/0 cycle.
In comparison to the 18/6 cycle, the 20/4 schedule gives your plants more light time. And as we just discussed, more light means faster growth. So if you place your autos on a 20/4 you are likely to experience optimal yield results.


  • Reported better results in comparison to the 18/6 cycle
  • Allows your plants time for rest


  • Higher energy usage in contrast to 18/6

18/6 lighting cycle

The 18/6 lighting schedule is the most frequently used cycle when it comes to autoflowering strains. It is also recommended for growers new to growing with autoflowers.
Probably one of the best things about this cycle is that it’s great for growers who live in hotter climates. Those with experience using the 18/6 suggest keeping your lights on during the night. And to save on energy you can keep your lights off during the six hottest hours of the day.
Growers have reported this lighting schedule uses up to 25% less electricity compared to previously mentioned cycles. With the minimal use of electricity, and more rest time for your plants. The 18/6 method seems to be one of the most economically efficient and healthy ways to grow autoflowers.


  • Ample rest time for your autoflowers
  • Saves the most on electricity out of the cycles mentioned thus far


  • Having a timer is essential for this lighting cycle

12/12 lighting cycle

Traditionally the 12/12 lighting schedule is used for photoperiod plants. Growers tend to use the 12/12 method if they’re growing photoperiods’ alongside their autoflowers.
That being said, if you’re solely growing autoflower strains, this cycle is not recommended. We mentioned previously that at minimum your autoflowers should receive 18 hours of light a day. If you’re not provided your plants with at least the bare minimum, they will not grow to their full potential.
Remember, the more light your plant is exposed to, the more it will grow. On a 12/12 cycle, autos will end up smaller and produce lesser yields.


  • Great for when growing both photoperiod and autoflower strains together
  • Least amount of electricity usage, good for growers on a budget


Your autoflowers will not grow to their full capability and produce less overall

Things to consider when deciding on a light cycle


We’ve taken a look at the pros and cons for each cycle discussed today. It’s not hard to see why the top-recommended cycles for autos are the 18/6 and the 20/4.
Even so, there are still some other topics to consider when deciding which light cycle best suits your needs. Let’s take a closer look at some we’ve mentioned below.

Temperature concerns

When deciding on a lighting cycle keep in mind your location’s typical climate temperatures. As mentioned in the 24/0 cycle, it is best suited for colder climates. And again, the 18/6 cycle is best suited for hotter climates.

Overall cost

With the light cycles discussed today, we touched on a few that have higher energy costs. Growers with experience know that energy costs are just one of the many things to consider in your overall budget.
Therefore, keeping your budget in mind is always a good rule of thumb. It’s important to factor in any costs that might occur, both before and during your grow op.

Your schedule & time management

If your decided lighting cycle doesn’t require a timer, your schedule plays a big role here. Time management is a necessity for all growers. Be sure to prepare whatever your day-to-day schedule might be with the tasks that come with growing.

Wrapping up our guide on the best autoflower light cycle


Overall there is no such thing as a “best lighting cycle” for your autoflowers. True there are some that will inevitably provide you with the best results for your plants. But as you can see, it all depends on your needs and desires as a grower. Likewise, the autoflower strain you choose can play a role.

Now that you’ve got this knowledge under your belt, it’s time to put it into practice. Experiment with which lighting cycles work best for your plants. Heed our advice while you do, so that you don’t stress the strain. Who knows -- an uncommon lighting cycle may be the one most ideal for you.