Experienced growers are well aware of that using grow lights is one of the necessary ways to keep plants thriving indoors, and it can make your plants grow more efficiently. But they can also be harmful to plants if the correct lighting schedule is not followed.

Many people fall into such a misunderstanding when using grow lights: since the light of grow lights can promote plant growth, is it recommended to keep plant lights for 24 hours? The answer to the question is of course no, and the ideal way is to leave the plant light on for 12 to 18 hours. Next, I will explain the reasons from several aspects.

What happens if putting a plant under a plant light for 24 hours?

Imagine that plants need daily rest just like humans and animals. When plants absorb a lot of light, they will continue to photosynthesize which will provide enough light for plant growth. The downside, however, is that if your plants are constantly exposed to light, especially during the growing phase, they may be under too much stress. Likewise, if your plants are exposed to intense light for extended periods of time, maybe it can cause your plants to burn.

Length of the Light-Dark Cycle and Plant Growth

Plants will thrive if they receive about 8 to 16 hours of light, whether artificial or natural. They need water, carbon dioxide and light to produce glucose, which is their food. When growing indoors, it’s important to determine how to control the light. Therefore, keep in mind that various plants require different light levels and concentrations.

Understand Photosynthesis and Respiration in Plants

What is photosynthesis? Plants absorb light and convert it into energy. At night, when everything goes dark, the respiration converts this energy into carbohydrates for later use. It means that exposing plants to light 24 hours a day can prevent respiration from occurring, which is also not conducive to healthy plant growth.

What’s the ideal amount of light exposure for plants?

The ideal amount of light for fruits or vegetables is 20 to 40 moles per day. Generally speaking, you can use LED grow lights with a PPFD value of about 308 micromoles during the growth stage. During the flowering stage, due to the shortened light cycle, you can choose LED grow lights with a PPFD value of about 462 micromoles.

Conclusion: leaving the lights on 24 hours – yes or no?

Turning on your grow lights 24 hours a day will increase the total amount of light your plants receive during the day, resulting in faster growth. But your plants may be weaker and more prone to disease. Therefore, don’t rush to give your plants too much light, but rather give them a break sometimes, and you may have a pleasant surprise.