Can You Leave Grow Lights On 24 Hours A Day (Is It Recommended?)

It might be challenging to provide your plants enough light when growing indoors. However, using grow lights allows you to increase the length of your growth season and help your plants thrive while inside.

Plant grow lights are an excellent tool for increasing the productivity of your growing process, but they can also be damaging to the plant if the correct lighting schedule is not followed.

Can You Leave Grow Lights On 24 Hours A Day (Is It Recommended)

It could be tempting to leave the lights on for 24 hours, but your plants will suffer as a result.

In this article, we will go into further detail on whether you should leave your grow lights on 24 hours a day. 

What Happens If You Leave Grow Lights On 24 Hours? 

The longer plants are exposed to light, growers believe, the greater their crop will be. During the initial weeks of the vegetative stage, some people even leave grow lights on continuously.

Although they are right that more light is needed, you need to take a few things into account, like the weed strain, kind of light, and development stage.

It is feasible to leave grow lights on continuously, however, scheduling lighting schedules throughout the day is far more preferable.

Plants also require a respite from direct light, just like people and animals do. When cannabis is exposed to a lot of light, photosynthesis occurs continuously. On the plus side, the leaves will grow at its fastest rate as a result.

However, there are also negative effects. Your plants may become stressed if they are exposed to light all the time, especially when they are in the vegetative stage.

If they are stressed, they may develop diseases, which can lead to pests and eventually death. 

How Many Hours A Day Should A Grow Light Be On? 

In order for cannabis to grow, it requires a minimum of 13 hours of light each day, whether this is natural or artificial light. To promote quicker development, indoor gardeners frequently adopt an 18/6 light-to-dark ratio.

Thus, grow lights will usually be on for up to a maximum 18 hours a day. 

Then, once your cannabis plants are ready to blossom, a 12-hour cycle of light and darkness is typical.

For this reason, indoor gardeners deliberately make an attempt to mimic dark cycles in addition to long, bright days in order to encourage the development of huge, dense buds in cannabis.

If you opt for the traditional 12/12 light schedule, you must stick to it religiously. Otherwise, you may risk stressing your plants out, and they won’t be receiving the right amount of light. 

Can You Leave Grow Lights On 24 Hours A Day (Is It Recommended) (1)

Can Plants Tolerate 24 Hour Light?

Plants will absorb light and use it as an energy source through photosynthesis. As soon as it gets dark at night, respiration converts that energy into carbs for subsequent use.

This means that giving your plants constant access to light will stop them from respiration.  Thus, if you leave your plants in 24 hour light, then they will not be able to respire, and this will affect the overall health of your plants. 

You may be able to leave the plants in 24 hour light for a few days, but any more than this will have a negative effect. 

Is 12 Hours Of Grow Light Too Much?

While grow lights are great for your plants, nothing beats natural sunlight from the sun (Also check out How To Choose A Ballast For Growing Cannabis)

. However, the amount  of sunlight you receive can vary on a day-to-day basis and depending on where you live. This is why grow lights have become so popular.

A lot of growers will provide their plants with light for 24 hours, but this will cause your plants to grow far too quickly. These plants will grow much better when they receive between 10 and 12 hours of sunlight or grow light a day.

However, as mentioned above, the type of plant you are growing will affect how much light it needs. 

Factors That Will Affect Your Grow Lights

When you are planning to leave your grow lights on, there are a couple of factors you need to keep in mind. 

Type Of Plant

There are three different types of plant, which all require different lighting requirements. Around 4 hours of artificial light each day should be provided for low-light plants.

Medium-light plants, on the other hand, require roughly six hours of light. High-light plants, meanwhile, require 14 to 16 hours of light every day.

Growing Stage

Each stage of the growth of your plants will require certain light needs. The vegetative stage requires the most amount of light, which can be up to 18 hours. This will then reduce to 12 hours, once you hit the flowering stage. 


Lights have an effect on humidity and temperature. The recommended temperature range for a grow room is between 72 and 82 degrees Fahrenheit. The humidity levels must be between 30% and 40%.

Type Of Grow Lights

The type of grow lights that you use can affect the amount of light exposure the plants receive. This in turn could impact how long the lights need to stay on for.

LED grow lights are seen as the best types of grow lights to use as they support photosynthesis. However, there are lots of different lights out there you could use as well. 

Final Thoughts

Apart from when your plants are in the vegetative stage, it is not recommended to leave your grow lights on for over 24 hours. This is because the long exposure to the lights will cause your plants to grow quickly.

Your plants  won’t be able to respire, which can promote diseases and pests and eventual death. 

We hope this article has been informative and helps you to understand how long you should be leaving your grow lights on for. 

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