Can You Leave Grow Lights On 24 Hours a Day?

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Can You Leave Grow Lights On 24 Hours a Day

Providing enough light to the plants in your grow space is essential. LED grow lights can extend your growing season and make your plants thrive. Some growers leave their grow lights on 24 hours a day because more light generally means more growth and more yields. There is no doubt that leaving your lights on longer will lead to faster growth. But does 24 hours of light really increase yields?

In this article, we will take a deep look at it. Can you leave your grow lights on 24/7? What effects do 24 hours of uninterrupted light have on your plants?

Can You Leave Grow Lights On 24 Hours A Day?

The quick answer is no. Plants cannot be exposed to 24 hours of light, be they long-day plants or short-day plants. It will have a negative impact on their growth.

Disadvantages of 24/7 Lighting

No Rest Time

No Rest Time

The downside of 24/7 lighting is that your plants have no rest time. Undoubtedly, all-day light can make your plants grow faster. However, if you do this in the long term, your plants will become increasingly weaker and more susceptible to disease.

Plants also have a routine. During the day, plants photosynthesize carbon dioxide and light from the sun or artificial grow lights into sugars. At the same time, they release oxygen, and they are also breathing. When they are in the dark, they stop photosynthesizing and focus only on breathing. When they breathe, they convert the sugars they generated during the day into energy. They use this energy, as well as nutrients from the soil, to support their life.

Photooxidative Stress

Too much light will produce reactive oxygen species (ROS), damaging plant cells, and even causing cell death.

Decomposition of Chlorophyll

Excessive light can cause the decomposition of chlorophyll in the leaves, resulting in reduced photosynthetic capacity and slow growth.

Additional Costs

It costs more money to keep the lights on all day. You’ll need to pay for the electricity to power your grow lights, as well as the electricity to power fans, air conditioning, and any other equipment you might run in your growing space. You’ll also need to replace bulbs more frequently.

Additional Stress on Equipment

Leaving your lights on 24/7 also means that the grow lights and other equipment are always running, which puts stress on them and shortens their lifespan.

Additional Heat

Additional Heat

Having your lights on all the time creates more heat. This means you’ll also need to run fans and other cooling equipment for 24 hours. Otherwise, your plants are at risk for burn.

Inefficient Water Use

Excessive light may also cause your crops to lose more water through transpiration, increasing the chance of drought.

Reduced Nutrients

All-day light can also damage the roots of your crops, which hinder their ability to absorb nutrients from the soil, thus thwarting plant development.

How Long Should Grow Lights Be On?

How Long Should  Grow Lights be On

It mainly depends on the following factors:

  • Plant Type
  • Growth Stages
  • Types of Grow Lights

Plant Type

Generally speaking, plants need about 12 hours of light per day to thrive, and some species will need more. Let’s check it.

  • Tomatoes: 12-16 hours 
  • Cucumbers: 12 hours
  • Peppers: 12-16 hours 
  • Marijuana: vegetative stage: 18-24 hours; flowering stage: 12 hours
  • Succulents: 14-16 hours
  • Herbs: 12-16 hours
  • Lettuce: 12-14 hours
  • Strawberries: 14-16 hours 

Growth Stages


  • Seedling stage: During this stage, strawberries require low to moderate light. It is best to have your grow lighting running for about 12-16 hours.
  • Vegetative stage: Strawberries require higher light levels in this stage. 14-18 hours of light per day is advised.
  • Flowering stage: Strawberries need more light at this stage. It’s best to provide them with 16-18 hours of light.
  • Fruiting stage: Strawberries, eager to enter the fruiting stage, need moderate to high light intensity. 12-14 hours of light is advised.

As your strawberries grow, it is vital to monitor them and adjust your LED grow lights. This includes adjusting light intensity and the mounting height. Wild strawberries and June strawberries have various light requirements. Please check their specific light requirement carefully.


  • Seeding stage: Succulents require direct bright light to successfully germinate. A succulent grow light with an intensity of 200-400µmol/m²/s and a color temperature of 5000K-6500K is suitable for this phase.
  • Vegetative stage: Grow lights with an intensity of 400-600µmol/m²/s and color temperature of 5000K-6500K are best.
  • Flowering stage: Succulents require the most intense light during this phase. A grow light with an intensity of 600-800µmol/m²/s and a color temperature of 2700K-3000K is ideal for this phase.

Some types of succulents can tolerate less light. It’s best to check the specific needs to ensure they get enough light. For their health, make sure your succulents aren’t exposed to too much direct sunlight. If you notice any signs of burns, such as brown spots or leaf burns, you may need to move your succulents to a slightly shadier location.

Types of Grow Lights

LED Grow Lights

They produce a specific but complete spectrum of wavelengths, and while LED lights can emit intense light, they consume very little energy, so there’s no need to worry about your electricity bill.

Regular Light Bulbs

Regular light bulbs are energy-efficient and have a long lifespan. They’re also inexpensive. However, regular lights have a narrow spectrum of wavelengths and tend to heat up easily. They have a hard time getting plants to bloom.

Compact Fluorescent Lights

You can place CFLs about 6-7 inches away from your plants. However, unlike LED lights, CFLs don’t come with a cooling system.

High-Intensity Discharge Lights

HID lamps are the top choice for growers on a tight budget. They’re known for their high-intensity discharge, which gives off a lot of light per watt. However, the bulbs emit a lot of heat, which can burn your seedlings. Also, they’re not as powerful as LED lights.

Final Thoughts

Keeping your grow lights on 24/7 will increase the amount of light your crops receive, which can speed up growth. But your plants will be damaged and more susceptible to disease. It also increases additional costs.

If you want to increase the amount of light, you should buy additional grow lights or replace your current lights with more powerful ones. This will give you better outcomes than if you just left the lights on all the time. And I recommend Casyoo LED grow lights. Talk to us

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Anne Zhang

Anne Zhang

Anne is a senior electronics engineer at Casyoo, a professional LED Lighting solutions manufacturer. With 10+ years of experience in the LED grow lighting industry, she aims to help growers and researchers around the world get a better understanding of LED grow light technology so as to increase their crop yields.
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