Ideal Light Cycles for Growing Cannabis


Light cycles are often neglected when growing cannabis since many novice growers are not knowledgeable about how cannabis plants can be sensitive to light. Lighting and light cycles is a crucial and significant factor in successfully growing your marijuana – and this applies to both indoor and outdoor growing. With this, it is very important for you to know as to which light cycle and for which phase or stage should you be using in growing your cannabis.

The light cycle you use for your cannabis growing directly affects your plant’s quality and overall yield. You have to know that there are two stages of cannabis growth when it is very significant to effectively monitor your light cycles. The two stages, which will be discussed in detail later on, are the vegetative and flowering stages.

Naturally, the flowering phase of cannabis plants falls between the end of the summer and fall season. This is when the dark hours are significantly longer than the light hours, for indoor growing. It is very important to alter the light cycles to stimulate the blooming of cannabis plants. Two separate rooms should be prepared for indoor gardens to keep plants of different growth phases or stages separated from each other.

This post will help you guide you as to which light cycles will work best during the respective cannabis growth stages.

Read more about growing here.

Light Cycle for Vegetative Stages

The vegetative stage is generally the stage of a phase where your cannabis plants are thriving to grow, and there are two types of light cycles that are popularly used during this stage. The first one is 24 hours, and the other one is 18 hours. You must pick the appropriate light cycle since this stage is vital for the health and successful growth of your cannabis plant.

During the vegetative stage, the stems and leaves of your cannabis plants will now start to grow out to become large and tall. The plants will not produce buds at this stage, but it is important to have your plants in a controlled size and shape. To effectively do this, you should put up a light cycle that can be manipulated to yield better growth. In the vegetative stage, the more lighting results in better growth and good future yield.

The recommended light for cannabis plants in the vegetative stage is a minimum of 18 hours under growing light, or also known as 18/6. But if you desire to have your cannabis plants grow bigger than ever, you can put them under 24/0 or 24 hours under growing light. Many growers prefer the 24/0 since it is known to push the cannabis plant to perform photosynthesis incessantly. Cannabis plants won’t start the flower development stage until they start under 12 hours of continuous darkness. Otherwise, your plants will stay in the vegetative stage.

Most growers will start growing their cannabis plants indoors under a light set up before transferring them outdoors. March and April are the best months to start seeding or cutting clones and keep them under 18 hours or 24 hours of light cycles before transferring the plants outside when the month of May or June arrives.

Please note that before growing your cannabis outdoors, you must keep them away from dangerous climate or weather such as frost or heavy snow. A significant and significant change or drop in temperature will surely kill your cannabis plants right away.

When growing indoors, you should pay attention not only to the light but also to have a well-maintained grow room with a high enough ceiling to accommodate healthy plant growth. When growing indoors, it is important to note that certain strains might be needing more attention than the others, and might even need a more specific light cycle.

Light Cycle for Flowering Stages

Similar to the vegetative stage, the flowering stage also requires different light cycles. Many growers are inclined to use 12 hours of light and 12 hours of total darkness since this light cycle can give the best outcomes. You need the darkness phase since 12 or more hours of darkness is required for your plants to be able to move from their vegetative stage to the flowering stage.

When growing your cannabis outdoors, the easiest and the best way to do it is to let nature do its part. During this stage, your cannabis plants will be able to bloom and start flowering on their own, with the help of mother nature. This usually happens during the last days of June, when days eventually become shorter and nights are longer.

When growing outdoors, make sure that your plants will not be exposed to any form of light on the times when they should be in complete darkness. Any form of intense or bright light may seriously disturb the flowering patterns of your cannabis plants.

To successfully grow cannabis plants in an indoor setting, you may need to mimic the natural growth pattern. Flowering or the development of buds will start during the shorter days, and they receive a minimum of 12 hours of total darkness. For effective growing, you will need to shift your light usage from 18 to 24 hours of light daily, down to 12 hours of light and 12 hours of darkness.

Light Cycle Schedules for Maximum Yield

You must establish a good light cycle and lighting plans so that you will be able to achieve maximum yield from your cannabis plants. For indoor growing, you should let your plants stay under 24/0 or 18/6 light cycle. This light cycle should be continued for up to two months or 60 days. This light cycle is applicable when growing outdoors, but always remember to protect your plants from extreme weather conditions. From the time you successfully finished your cannabis plants’ vegetative stage, and have prepared your plants for its flowering stage, be ready to harvest a great yield from your plants.

The ideal light cycles vary based on the stage of growth:

  • Seedling Stage

During this initial stage, cannabis seedlings thrive under a light cycle of 18 hours of light and 6 hours of darkness (18/6). This can be achieved using inexpensive grow lights like LEDs or fluorescent bulbs. If growing outdoors, ensure that seedlings receive at least 18 hours of natural light, supplementing with artificial light if necessary.

  • Vegetative Stage

In the vegetative stage, cannabis plants require plenty of light for healthy growth. Indoors, a light cycle of 18/6 is typically used, although some growers may extend this up to 24 hours of light (24/0), though this can lead to rapid, less efficient growth and higher electricity costs. Outdoors, the plants should receive at least 18 hours of sunlight, or be kept under grow lights until the outdoor conditions are favorable.

  • Flowering Stage

For the flowering stage, the light cycle shifts to an equal duration of light and darkness, 12 hours on and 12 hours off (12/12). This change in light cycle mimics the natural decrease in daylight hours and triggers the plants to start flowering. Indoors, this can be controlled with timers. Outdoors, nature typically takes over as the days grow shorter. Some growers have experimented with a slightly altered cycle of 11 hours light and 13 hours darkness (11/13), which may improve flowering and trichome production, though evidence is anecdotal.

  • Autoflowering Cannabis Plants

Autoflowering cannabis strains are less dependent on light cycles to transition to the flowering stage. They can be grown under longer light cycles during flowering, such as continuing the 18/6 cycle throughout their lifecycle. This can potentially increase yields but also raises electricity costs.

  • Additional Considerations

The choice of grow lights and their placement is also vital. For instance, CFLs are suitable for seedlings and vegetative growth, while HIDs and LEDs are better for the vegetative and flowering stages due to their intensity. The distance of the lights from the plant canopy is important to avoid stress or burning the plants.


There are tons of benefits when you grow your cannabis plants. However, it would help if you remembered that you would only acquire the best yields and great harvest when you use the appropriate light cycles used during the growing and blooming phase of your plants.

We hope you were able to learn a lot from this post and grow your cannabis plants successfully and healthily.