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Should I Leave Grow Lights On 24 Hours A Day?

by in Grow Light Advice February 27, 2018

Providing sufficient light to your plants inside a grow space can be tricky, but using Grow lights enables your plants to thrive indoors and extend your growing season.

Plant grow lights are a great tool to make your growing process more efficient, but they can also be harmful to the plant if dont follow the proper lighting schedule.

Now you might be wondering – how long should you keep grow lights on or if it is recommended to leave grow lights on for 24 hours?

The answer to the question is no, it is not recommended to leave your grow light 24 hours a day, because this will force plants to grow quickly. It is ideal to keep a grow light on for about 12 to 18 hours.

Too much light in various growth phases can interrupt a weed plants natural process of growth and dormancy. Worse, light exposure for a whole day can damage and kill your plants.

What Happens If I Accidentally Leave the Grow Lights on for 24 Hours?

24hours grow light

One of the most often asked question from new growers is from those who accidentally leave their grow lights on for more than 24 hours. Leaving the lights on for too long is actually a common problem.

Its often due to a malfunction in the timer, the timer breaking, or forgetting to shut the timer off manually.

If the plants are in the vegetative phase, generally it is not an issue if they are overexposed light. Nonetheless, 24 hours of light is really not good for production.

However, overexposure to light will not kill your plants.

Some growers believe that seedlings need 24 hours of light. But in actuality, many experts recommend that you give seedlings 12 hours of light and 12 hours of dark.

On the other hand, some specialist feels that your seedlings need 16 hours of light, depending on the variety.

Length Of The Light-Dark Cycle And Plant Growth

There are basically four growth cycles of a cannabis plant. Each growth cycle requires a certain amount of light and dark for optimum plant growth and higher yields.

  • Germination – cannabis seeds do not need light to germinate. In fact, they require complete darkness for successful germination.
  • Seedling – once the seeds have sprouted, the seedling will need a lot of light. Seedlings need 18 to 24 hours of light, depending on preference and the strain.
  • Vegetative stage – Indoor growers typically give their plants either 18 hours of light and 6 hours of dark each day or 24 hours of light with no darkness.
  • Flowering stage – the flowering stage generally requires 10 to 12 hour light/dark cycle.

In addition, cannabis does not respond well to extreme temperatures. For the best growth, avoid colder temperatures. During the vegetative stage keep temperatures in your grow tent between 68°F to 86°F (20-30°C).

During the flowering stage, ideal temperatures should be between 68°F to 77°F (20-25°C). Likewise, perfect humidity levels should stay between 40% to 60% humidity.

Should Autoflowers Have 24 Hours of Light?

autoflower canabis

Autoflowering marijuana plants need time to rest, just like any other plant. The main difference with auto-flowering cannabis strains is that they switch to flowering automatically. They do not need you to shorten the daylight hours to tell them when to switch.

Theoretically, you could run the lights 24/7 even during flowering, but you shouldnt. However, you can run them on an 18/6, or even a 20/4, cycle during the bloom stage, the same as during vegging.

Should Seedlings Get 24 Hours Of Light?

No, they should not. Seedlings also need a dark period. We recommend leaving the lights on for 12 to 16 hours a day for seedlings, with our preference being 16 over 12.

Why do People Leave Grow Lights on for 24 Hours?

For most growers, their main objective is production and yield. It stands to reason that the more light a plant gets, the more it produces. With this in mind, some growers leave their lights on 24/7.

Although it is true that more light will produce more yields, its the type of light that needs to be monitored. For the most part, the strength of a grow light and the amount of light given to a plant will produce better yields.

If your plants have stunted growth, it is usually best to upgrade the type of grow light you are using instead of increasing the number of light hours. Generally, you need to buy a stronger grow light that has good light intensity.

The Best Lighting Schedules For Cannabis

grow lights for cannabis

Well start with flowering because there is no flexibility to increase the daylight hours during this stage. Your lights need to be off for 12 hours per day (with the exception of autoflowers, of course). Keeping them on longer can result in your weed plants switching back to vegging and then youll have a hard time getting them to flower again.

During vegging, you have much more flexibility. It is perfectly possible to leave the lights on overnight, but as mentioned, it is best to give your plants at least some darkness.

The most common lighting schedule during vegging is 18 hours of light and 6 hours of darkness. This is the schedule we recommend. 20 hours on and 4 hours off works well, too.

Another interesting option is to use a 6/2 light schedule. What this means is you leave the lights on for six hours, then turn them off for two. You have 3 of these cycles per day. You still end up with 18 hours of daylight and 6 hours of darkness, but they do not all fall at once.

Leave Grow Lights On 24/7: Final Thoughts

Yes, you can leave grow lights on 24/7. Typically this is done during the vegetative stage of growth.

Moreover, your plants will grow rather big and have a lot of foliage plus stem height.

Nevertheless, most plants including cannabis will greatly benefit from a light and dark cycle. In fact, your plants will be a lot healthier and robust.

Likewise, during the flowering stage, cannabis requires12 hours of light and 12 hours of dark to produce good buds. Quite frankly, the most potent and large buds come from plants that have a balanced amount of light and dark.

Overall, 24/7 light can be productive during the vegetative stage of growth, just be careful not to overdo it. If your plants receive too much light during this stage, they will be prone to disease and have a lower yield.

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