How Much Light Do Autoflower Cannabis Plants Need?

How Much Light Do Autoflower Cannabis Plants Need?
How Much Light Do Autoflowers Need
How Much Light Do Autoflowers Need

Shedding Light on Autoflowering Cannabis Plants: Understanding Their Lighting Requirements

Autoflowering cannabis plants have rapidly gained popularity among cultivators due to their speedy growth cycle, compact size, and resilience. One of the most appealing aspects of these plants is their ability to flower independently of the light cycle, which simplifies the growing process. However, proper lighting remains essential for the healthy growth and development of autoflowering plants. In this article, we will explore the lighting requirements for autoflowering cannabis plants, including recommended light schedules and intensity, to help ensure a successful harvest.

Light Schedules for Autoflowering Cannabis Plants

Unlike photoperiod cannabis plants, which require a change in the light cycle to initiate the flowering stage, autoflowering plants begin to flower based on their age. This unique trait allows growers to maintain a consistent light schedule throughout the entire growth cycle. The most common light schedules for autoflowering plants are:

18 hours on, 6 hours off:

This is the most widely used light schedule for autoflowering plants, providing a balance between energy consumption and optimal growth.

20 hours on, 4 hours off:

Some growers prefer a 20/4 light schedule, believing that the additional light exposure can boost growth and yield potential.

24 hours on:

In theory, autoflowering plants can grow under continuous light, but this approach can be less energy-efficient and may increase the risk of stress or diminished returns on growth.

Light Intensity and Spectrum

Autoflowering plants require sufficient light intensity to thrive. While they can tolerate lower light levels than photoperiod plants, providing optimal light intensity will promote healthy growth and larger yields. The following are some general guidelines for lighting autoflowering cannabis plants:

Seedling Stage:

During the first couple of weeks, seedlings need gentle, diffused light. A lower intensity of around 300-400 PPFD (photosynthetic photon flux density) is appropriate at this stage.

Vegetative Stage:

As the plant enters the vegetative phase, it requires more light to support its growth. Increase the intensity to 400-600 PPFD to encourage robust development.

Flowering Stage:

During the flowering phase, the plant’s light requirements peak, with an ideal intensity of 600-900 PPFD. This level of light will support the development of dense buds and potent trichomes.

In addition to light intensity, the light spectrum plays a crucial role in plant development. For autoflowering plants, a full-spectrum light source that mimics natural sunlight is highly recommended. LED grow lights are a popular choice among growers, as they offer adjustable spectrums, energy efficiency, and longevity.

Adjusting Light Distance and Positioning

To ensure that your autoflowering plants receive the right amount of light, it’s essential to position the light source correctly. Keep in mind that different types of grow lights emit varying levels of heat, which can impact the ideal distance between the light and the plants. The following are general guidelines for common grow light types:

LED lights:

Position 30-60 cm away from the plants.

CFL (Compact Fluorescent Lights):

Place 15-30 cm away from the plants.

HPS (High-Pressure Sodium) and MH (Metal Halide) lights:

Maintain a distance of 40-80 cm from the plants.

As your plants grow and develop, it’s essential to adjust the height of your lights to maintain the appropriate distance. If the lights are too close, they can cause heat stress or light burn, resulting in stunted growth and damage to the foliage. Conversely, if the lights are too far away, the plants may become elongated and weak as they stretch to reach the light source.

Monitoring and Adjusting Light Conditions

It’s crucial to regularly monitor your plants’ light conditions to ensure they’re receiving the proper lighting for their specific growth stage. To assess the light intensity accurately, consider using a PAR (Photosynthetically Active Radiation) meter, which measures the amount of usable light for photosynthesis.

Be mindful of any changes in your plants’ appearance or behavior, as these can signal issues with lighting. Signs of inadequate light may include slow growth, pale coloration, and stretching, while excessive light can lead to curling or wilting leaves and light burn. Regularly checking and adjusting your lighting setup can help you address these issues and optimize your plants’ growth.


Understanding and meeting the lighting requirements for autoflowering cannabis plants is essential for a successful grow. By providing the appropriate light schedule, intensity, and spectrum, as well as adjusting the light distance and positioning, you can help your autoflowering plants flourish and produce a bountiful harvest. With careful attention to these factors, you’ll be well on your way to mastering the art of growing autoflowering cannabis plants.

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