Leaving Grow Lights ON For 24 Hours?

Grow Lights

If you are a newbie in the world of growing indoor plants, you might have a lot of queries in your mind that need to be answered. Growing indoor plants require proper equipment and management. After setting up the grow light properly, you need to know how long to keep your grow lights on. Let us provide you the best answer to your question, “What will happen by leaving grow lights on for 24 hours?”

Leaving grow lights on for 24 hours is not recommended. However, you can put them under light for 24 hours if they are in the vegetative phase. As plants require a balanced light and dark ratio cycle for their best growth and 24 hours of lights is not good for the plant’s respiration process. You can put the grow lights on for a maximum of 12 to 18 hours a day.

If you observe that your plants’ growth is not increasing by 12 to 18 hours of grow lights, you must change your grow light or you are required to check your plant’s supplements. As the plant is the main variable in the equation so every plant reacts to light differently and requires separate hours of light. You must be careful not to over doze your plant as it damages them and produces lower quality results. You can check out our article Decorative Grow Lights for Indoor Plants for further information about the type of grow lights suitable for your plants.

A Balanced light and dark ratio cycle for plants

Plants growth is also affected by the location. Outdoor plants that require 8-12 hours of direct sunlight may not survive indoor. Similarly, growing plants indoor demands more care and optimal solutions regarding growth and light exposure. Plants undergo certain biochemical processes in the growth process.

grow lightDuring the daytime, plants go through photosynthesis in the light that turns the light into the plant’s energy. During the nighttime, plants take the respiration process in the dark that turns the plant’s energy into carbohydrates which are stored for later usage by the plants.

These two processes occur at the specified time under the listed limitations. When you expose your plants to light for 24 hours per day, the respiration process is not performed. Resultantly, the plant’s growth is disturbed and it yields to unhealthy plants. So to support the natural process, you cannot leave grow lights on for 24 hours.

What is 12-12 lighting?

For the growth of plants indoor, your need to develop the seedlings into plants by scheduling the grow light at a certain pattern to provide 12 hours of light 12 hours of dark to your plants uninterruptedly. As the plant changes from seedlings to the flowering phase, they require 6 weeks to 5 months’ time duration to be kept in 12-12 lighting before the seedlings grow into buds and the buds are ready to harvest. You can check this video out:

How to manage the sufficient grow lights exposure on your plants?

Your plants require a certain darkness period to do rest. They utilize this time to turn their nutrients into the carbohydrates. You must know the fact that the majority of plants require 12 hours of light per day. You can provide the required amount of light to your plants by setting up the timer to turn them off. With this step, you do not have to worry about the plants’ exposure to light.

If your leaves start turning curly and yellow, you are overexposing the plants to grow lights. You can set an alarm at a specified time to turn the grow lights on and off. You can also hang a thermometer to check the room temperature and humidity. Using an excess number of grow lights can also result in less development.

Can you leave grow lights on for 24 hours?

You may accidentally leave the grow lights on for the whole day because of forgetting to turn them off or dysfunctionality of the timer. In this case, mostly two cases are considered i.e. the Vegetative phase and the Flowering phase.

  • Your plants can survive if they are at the vegetative phase at the moment. However, exposure to light for 24 hours is not recommended, it would not damage your plants as soon as they are undergoing the vegetative phase. Plants in the vegetative phase require more light for ultimate growth and need 18 hours of light and 6 hours of dark exposure.
  • Your plants do not have a good survival rate if they are in the flowering phase. In such a case, exposure to light for only 12 hours is enough. Moreover, it increases your plant’s risk to reenter the vegetative phase. The flowering phase requires 12-12 lighting methods for producing big buds.

A word on grow light’s intensity

indoor plantsIf you are talking about the amount of light you must also consider the intensity of light for indoor plants. Plants require the different intensity of light depending upon their type. You can observe that if a plant is yellowish, it is not getting the required amount of light. You can increase the intensity of the light for the proper growth. In contrast, plants also die after getting excess light. You can change the grow light location to increase or decrease the intensity of the light. You also choose the type of grow light depending upon the light spectrum. It requires some knowledge about the spectrum of lights for plant growth. You must know what type of light provides enough warmth to your plants.

Consequences of leaving grow lights on for 24 hours

Leaving grow lights on for 24 hours does not support the development and growth process of plants. When it comes to indoor gardening, it is suggested that you cannot leave the lights on constantly during the life cycle of many plants. It does not help the plants to rest and breathe properly. Subsequently, the root growth and fruiting capacity of plants reduce. As plants are living things just like human beings. So, the plants require complete rest and sleep for their growth just like us. This means that leaving grow lights on for 24 hours can limit the plant’s resting period for long-term healthy production. It can also overwork a plant. A plant grown in 24 hours light turns produces yellow leaves with brown lining between the leaf edges and the veins.


All in all, you can leave your grow lights on for 24 hours a day when your plants are undergoing the vegetative phase. It helps you grow your plants longer and increases the foliage volume and stem length. On the other hand, some plants follow the light and dark ratio cycle, particularly in the flowering phase. It helps you grow your buds’ width. You can also check this research paper for complete knowledge: “Study and optimization of lighting systems for plant growth in a controlled environment”.

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