Autoflower light cycle: Everything you need to know

Want to boost your autoflower cannabis yields? 

Mastering the autoflower light cycle is key. When you grow autoflower strains, if you don’t use the best light schedule, you risk stunted growth and lower yields. 

In this guide, we provide the solution to maximise your plants' growth and yield by understanding the right light cycles. 

We’ll cover everything from seedling to flowering stages with scientific insights and practical tips to ensure you get the best results. 

Dive in and learn how to set up your grow room for success and achieve your best harvest yet!

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so by the law and subject to appropriate permissions and licenses of the applicable country.

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What is a cannabis plant autoflower light cycle?

The autoflowering plants' light cycle refers to the specific pattern of light and darkness that you provide to your autoflowering cannabis plants. 

Unlike photoperiod plants that rely on changes in light to trigger flowering, autoflowering cannabis blooms based on age. This means you can expose them to more light when growing indoors to boost growth.

For example, while a photoperiod cannabis strain requires a 12/12 light schedule (12 hours of light and 12 hours of darkness) to flower, autoflowers can thrive with longer light exposure, making them perfect for growers looking to maximise yields by using specific light cycles.

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Different light cycles for autoflowering cannabis plants

Choosing the right light schedule for autoflower plants can significantly impact their growth and yield. There are several different light cycles indoor growers achieve great results with; here are the common ones:

18/6 light cycle autoflower

This light schedule provides 18 hours of light followed by a 6 hour resting period of darkness. Most growers use this balanced approach that promotes growth and flowering.

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Pros:

• Balanced energy use: This cycle reduces energy costs and can save money by providing less light hours compared to longer light schedules.
• Good growth: Provides enough light for healthy growth without overwhelming the plants.

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Cons:

• Moderate or slightly reduced yields: While growth is steady, it might result in somewhat smaller plant size and not maximise yields as effectively as longer light schedules. 

20/4 light cycle autoflower

The 20/4 light cycle provides 20 hours of light per day, followed by 4 hours of darkness. 

This cycle maximises light exposure, encouraging plants to grow faster and generate potentially higher yields. 

Many growers find this balance ideal, as it allows the plants to rest for a few hours while still benefiting from extended light exposure.

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Pros:

• Maximised growth: Increased light exposure promotes faster and more vigorous growth.
• High yield potential: Often leads to higher yields and can increase resin production due to extended photosynthesis periods.
• Reduced stress: The 4-hour dark period allows plants to rest and recover, reducing potential stress.

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Cons:

• Higher energy costs: Increased light use leads to higher electricity bills.
• Environmental demands Requires careful monitoring of a well-optimised grow space to manage  temperature and humidity to prevent plant stress​

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24 hour light cycle autoflower

The 24 hour light schedule means 24 hours of light per day throughout the plants' life cycle, providing non-stop light exposure to the plants. This method can push autoflowers to their growth limits, potentially speeding up the time from seed to harvest.

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Pros:

• Maximum growth: A continuous 24 hours of light can push plants to grow as fast as possible.
• Shorter growing time: This can potentially reduce the time from seed to harvest.
• Simplified schedule: No need to manage light and dark periods, which can simplify the grow setup.

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Cons:

• Diminishing returns: Over time, the benefits of constant light may plateau, leading to minimal additional gains.
• Stress and heat: Constant light can stress plants and increase heat, requiring advanced cooling and monitoring systems.

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Unconventional light cycles

Some growers experiment with unconventional light schedules, such as a 36-hour light schedule or 6 hours on, 6 hours off. These methods can be effective but require even more in-depth monitoring and adjustment.

As these are uncommon practices, there’s limited research to prove that these lighting schedules produce good results reliably. 

Extreme lighting schedules can disrupt the growth cycle of your plants. Unless you’re super experienced, err on the side of caution and use a proven lighting schedule.

When selecting a light schedule, consider your specific growing conditions and the capacity of your grow space setup. 

Always monitor your plants closely and adjust the light cycle if you notice signs of stress or suboptimal growth.

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Best light cycle for autoflowers

There's an ongoing debate about the best light cycle for autoflowers. Some growers swear by the 20/4 light schedule, while others prefer 24 hours of light. 

The key is to find a balance that works for your specific setup and strain. Research supports the effectiveness of various light cycles for autoflowering cannabis. 

For instance, a study published in "Horticultural Science" found that extending the photoperiod to 20 hours per day during the life cycle significantly increased biomass and yield compared to shorter light periods.

Additionally, studies on photoperiod plants and light intensity, such as those from the "Journal of Experimental Botany," have shown that longer light periods can enhance photosynthetic activity and plant growth, provided that the environmental conditions (temperature, humidity, CO2 levels) are optimised to support the increased metabolic activity.

Another study published in Frontiers in Plant Science highlights the importance of a balanced light cycle. It indicates that while continuous light can boost growth, it may also lead to photoinhibition and stress if not managed properly.

Ultimately, the best light schedule for autoflowers depends on your specific growing conditions, the strain of autoflowers you are cultivating, and your ability to manage the environmental factors in your grow space. 

When you grow autos, both the 20/4 and 24 hours light cycles have their benefits and drawbacks, and it is crucial to monitor your plants closely to determine which cycle works best for you.

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Recommended light cycle for autoflower seedlings

Starting with autoflower seeds requires careful attention to the light cycle. Seedlings must establish strong roots and promote growth. The initial seedling phase is crucial as it sets the stage for future development. 

Many growers use a 20/4 light cycle, providing 20 hours of light and 4 hours of darkness when growing autos. This ensures ample energy for photosynthesis and allows necessary metabolic processes during the dark period.

Blue light is vital at this stage, promoting strong vegetative growth and healthy leaves. Full-spectrum LED grow lights, rich in blue light, are highly recommended. 

Proper light management is crucial to avoid damaging delicate seedlings. Equip yourself with a PPFD meter and aim for PPF of 100 - 300 μmol/m²/s. Typically, keeping grow lights 60 - 75cm above seedlings works well, but adjustments might be needed.

Additionally, maintaining the right temperature, humidity, and VPD is essential. Ideal conditions include temperatures of 20-25°C (68-77°F), relative humidity of 60-70% and VPD of 0.5 - 0.7. 

Combining a 20/4 light cycle with blue-rich light and optimal environmental controls supports early seedling growth and lays a strong foundation for further development.

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Recommended light cycle for autoflowers in the vegetative stage

During the vegetative growth stage, autoflower plants thrive under a light cycle that maximises their growth potential. 

This stage is essential for developing a robust plant structure capable of supporting heavy buds during flowering.

Many growers opt for a continuation of the 20/4 light cycle and find that it helps maximise vegetative growth. 

This balance promotes vigorous growth without overwhelming the plants, ensuring they receive ample light for photosynthesis, which leads to strong stem and leaf development.

Again, full-spectrum grow lights, particularly those rich in blue light, enhance this stage by supporting the development of healthy leaves and stems, preparing the plant for flowering.

Maintaining optimal intensity of light and light spectrum is key to avoiding overexposure. Aim for PPF of 300 - 600 during veg. 

Additionally, adjusting environmental factors such as temperature (aim for …), humidity (aim for… ), and VPD (stay within the range of 0.7 - 1) to complement the extended light period further enhances growth.

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Recommended light cycle for autoflower in flower

As your autoflowering plants enter the flowering period, their light needs change to support bud formation and resin production. 

The light cycle for autoflowers in flower usually stays the same as during vegetative growth, but light intensity and spectrum are more crucial.

Many growers use the 20/4 light cycle during flowering, providing a balance of light and darkness to promote vigorous flowering while allowing plants to rest. 

Some opt for a 24 hours light cycle to maximise exposure, potentially increasing growth and yield, but this can raise heat and stress levels, so ensure your setup can handle these factors. Aim for PPF of 600 - 900+.

The light spectrum is especially significant during flowering. Red spectrum light promotes flowering and boosts resin production. Full-spectrum grow lights with an emphasis on red wavelengths enhance flower development and yield.

Proper intensity is essential to avoid overexposure, which can stress plants and reduce yields. Adjust the grow lights distance from the canopy, depending on your setup.

To prevent mould and mildew, maintain temperatures between 20-26°C (68-79°F), humidity levels of 40-50%, and a VPD of 1 - 1.4 with good ventilation.

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Environmental factors and light cycles

Your grow room environment significantly impacts how your plants respond to a different lighting schedule. 

Managing factors like lighting, CO2 supplementation, temperature control, and humidity is crucial for optimising growth and ensuring a healthy harvest.

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Lighting

Proper lighting is fundamental to plant health and growth. Understanding key concepts like Photosynthetic Photon Flux Density (PPFD), Photosynthetically Active Radiation (PAR), and Daily Light Integral (DLI) can help you provide the optimal light environment for your plants.

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PPFD

PPFD measures the amount of light (in micromoles) that hits a square meter per second. It’s crucial for understanding how much usable light your plants receive.

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PAR

PAR refers to the range of light wavelengths (400-700 nm) that plants use for photosynthesis. Ensuring your lights cover this spectrum is essential for growth.

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DLI

DLI represents the total amount of PAR received over a 24 hour period. It helps in understanding the cumulative light exposure your plants receive, which is crucial when using extended light periods like the 20/4 or 24 hour cycles.

Balancing PPFD, PAR, and DLI ensures your plants get the right amount and type of light without causing light stress or burn.

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CO2 supplementation

CO2 supplementation can significantly enhance growth, especially under high-light conditions. 

By increasing the CO2 levels in your growing area, you can help your plants handle higher temperatures and light levels more efficiently, leading to faster growth and higher yields. 

Plants use CO2 for photosynthesis, and higher levels can boost this process, provided other conditions like light and nutrients are also optimised.

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Temperature control

Maintaining the right temperature is crucial to prevent heat stress from high-power lights. Excessive heat can damage your plants and reduce their growth and yield. 

Fans, air conditioners, or heaters can help regulate the temperature and ensure a stable environment.

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Humidity management

Proper humidity levels are essential for preventing mould and mildew, which can devastate your crop. Dehumidifiers and humidifiers can help manage these levels effectively.

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Balancing environmental factors

Balancing these environmental factors with your light cycle will help your autoflowers thrive.

Monitor your plants with the Grow sensor or grow room monitor and adjust the conditions as needed to optimise growth and yield. 

Managing lighting, CO2, temperature, and humidity in your grow room can significantly impact the success of your autoflowering cannabis plants. 

Properly balancing these factors with your chosen light cycle will ensure your plants remain healthy and productive throughout their growth stages.

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Maximising yield with the best light schedule

Maximising yield involves finding the right light cycle that your plants can handle without diminishing returns. 

The Daily Light Integral (DLI) concept helps understand how much light your plants receive daily and its impact on growth.

Increasing light hours can boost yield, but only if your setup can support it. Consider if the additional light usage is worth the potential incremental gains.

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Takeaways

Choosing the right autoflower light cycle is essential for growing healthy, high-yielding plants. 

Whether you opt for the 18/6, 20/4, or 24 hour light cycle, balancing light exposure with environmental conditions is key. 

Experiment, monitor your plants, and adjust as needed to find the best setup for your grow room.

Happy growing!

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FAQs

What is the best light schedule for autoflowers?

The best light cycle for autoflowers is often considered to be 20 hours of light and 4 hours of darkness (20/4). This cycle maximises light exposure, promoting vigorous growth and higher yields. 

A study published in the Journal of Experimental Botany supports this, showing that extended light periods can enhance photosynthesis and biomass production in autoflowering cannabis plants. 

However, ensure your grow room environment is well-optimised to handle the increased intensity of the lights and heat.

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What light intensity is best for autoflowers?

It depends on the growth stage, but the best light intensity for autoflowering cannabis plants during the flowering stage typically falls within a range of 600-900 µmol/m²/s. 

This range promotes optimal growth and maximises yields without causing light stress to the plants. 

A study from Homegrown Cannabis Co. highlights that while 600-900 µmol/m²/s is excellent for flowering, experienced growers may push levels up to 1000 µmol/m²/s if their setup can handle it and they monitor plant responses closely.

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How far should my light be from my autoflower?

For autoflowering cannabis plants, the optimal distance for your grow light depends on the type and wattage of the light you're using.

It's generally recommended that LED grow lights be kept 60 - 75cm away from the plants to prevent heat damage and ensure adequate light penetration. 

This distance can vary based on the specific intensity and brand of the light, so it's crucial to monitor your plants for signs of stress and adjust as needed.​

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