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As we all know, other than water, warmth and humidity, light is the crucial component for creating good conditions for growing healthy and strong plants. They need the right quantity of light for photosynthesis which is very important for the energy they need for growth. When using artificial lightning, many of us wonder how long to keep grow lights on plants.

The optimal time to keep grow lights on plants is six to sixteen hours. But since the response to this common question depends on many factors, I will try my best to explain everything thoroughly. One thing is for sure, the idea of keeping grow lights on for a whole day, isn’t really good and can damage and kill your plants.

Sunlight vs Artificial Light

Sunlight vs Artificial Light

You may think that artificial grow light isn’t as good as the natural sunshine. While sunlight was very important before the development of technology, today we have a lot of high-quality artificial lights that have the same influence on your plants as the light produced by the Sun.

If you live in a colder area that doesn’t have enough sunshine, the grow lights can help a lot since they allow you to grow beautiful plants indoors. It’s always better to use different colour ranges, since the sunlight delivers a lot of different colours, even though your plants will grow just fine even with only one colour.

One of the advantages of artificial light is that you can monitor it and keep an eye on its intensity, while with sunlight that’s not an option. Some plants grow well next to a window, while some of them need special, monitored conditions, and grow lights can help with that. Here is the list of the best grow lights to help you with that!

How Long to Keep Grow Lights on Plants

There’s not a simple response to this question as it depends on many factors. In the first place, different kinds of plants and seeds require a different amount of water and warmth, they also require different light concentration and exposure.

A lot of houseplants and flowers thrive after being on grow lights for sixteen hours, but there are also some of them that need only six hours under the same lights. That’s why you should do research on the plant you want to purchase, not only because of the light but also because of the other factors such as watering and soil.

Dark time is as important as the time spent in the light because it allows the plants to consume all the energy they had previously produced. It’s the same with sunlight – it is not available for 24 hours, plants also grow during the night and need that rest to grow stronger.

Other than the plants’ requirements, the light exposure depends on other things as well – light concentration, the grow light you choose and colour range of the light.

Different Types of Plants and Light Exposure

Different Types of Plants and Light Exposure

If you’re unsure about your plants’ needs when it comes to light exposure, I’m going to write those that I consider the most popular plants that the majority of plant lovers own.

Aloe Vera, Orchids, Lettuce, Spinach, etc.

These plants require long light exposure. They will grow its best only if they are on grow lights for up to 16 hours per day.

African Violet, Dumb Cane, Chinese Money Plant etc.

The plants that are in the middle and need around 10-12 hours of light exposure during day require medium light exposure.

Tomatoes, Peppers, Snake Plant etc.

Finally, in the third category are the plants that grow great with less light exposure and when receiving light for only 6 hours. These plants prefer higher light intensity for a shorter period of time, so they have dark time to consume the energy.

Light Intensity

After checking the number of hours on grow light your plants need, you should also look for a light power they require. Some plants like being exposed to low power for a long time, while some of them prefer higher light intensity for a few hours.

Before installing the lights, make sure you know the preferences of the plant you want to nurture. A lot of manufacturers offer lights with the intensity that can be modified so look for those when purchasing it. You can also change the distance between the plants and light to control the intensity.

Types of Grow Lights

Types of Grow Lights

Different needs require different types of grow lights. All of the previously mentioned conditions and characteristics depend on the kind of light you initially choose. There are a few kinds of grow lights you can find on the market: HID grow lights, LED lights, Fluorescent lights, Sulfur Plasma lights, Induction lightning etc.

And while the choice depends on the plants and space you have for your indoor garden, the most popular types are the first two – HID and LED grow lights. At first, I can say that I didn’t understand the difference between these two.

After trying both of them I came to a conclusion that HID grow lights are better for plants that require more light exposure since they produce a lot of heat, so they are also great for plants that like warmth. If you have a lot of space and can keep the grow lights higher from the ground, HID lights will work great for you.

LED lights, however, are better for smaller plant and germination stations. They don’t heat up a lot, and you should buy these if you have plants that grow fine with less light exposure. What I like about LED lights is that they save energy and keep my bills low.

Too Much or Not Enough Light

The same as over-watering, too much light can be bad for your baby plants and flowers, and plants in general. If you leave them under grow lights for too long, or under the light that has strong intensity, the plants can start drying out and eventually die.

This happens because the plant is creating more energy than it can consume. This happened to me a few years ago, and I noticed yellow marks on the leaves of my tomatoes. I immediately reduced their light exposure, and they came back to normal after a couple of days.

On the other hand, if your plants don’t receive enough light, they won’t make enough energy, and they’ll die. So be sure to do thorough research and provide enough light for every plant according to its requirements.

Germination and Grow Lights

Germination and Grow Lights

Even if you prefer having your plants on the sunlight, grow lights can be a great technique of having a jump start when it comes to the seeds. A nice germination station consists of a heating mat, tray, planters, dome but most importantly – grow lights.

This will help the seeds grow better towards the light and develop healthy and strong roots with the energy they produce thanks to those same lights. Be sure not to over-expose the seeds since the same rules apply as with the plants when it comes to the water and light requirements.

Tips That Can Help

Tips That Can Help

Plants need a routine, and they love receiving light every day at the same time. That’s why you should remind yourself to switch on the grow lights and switch them off after the right period of time. You can always set the alarm to remind you when to do it.

However, if you’re okay with investing more money, you can purchase a timer that will make sure the lights switch off and on automatically. This is a great device if you need to travel and need something to take care of the light exposure of your plants.

I purchased it a few weeks ago, and I can assure you it will help you a lot because you’ll be able to relax, and you won’t have to organize your schedule according to the grow lights in your home!

Related Questions

1. What will happen if I leave the lights on for 24 hours?

As said, your plants and seeds will most likely die. Although some plants that need a long exposure to lights won’t mind it and it won’t affect them too much, other plants that prefer dark will find this stressful which will cause their death.

2. Is the sunlight enough?

If you’re blessed with sunny days during a whole year, then most likely yes! If, however, you live in areas that are darker and colder, grow lights will work wonders, and your plants will thrive even indoors.

3. What should I do when I notice yellow marks on the leaves?

As mentioned, noticing yellow marks means that your plant is too exposed to the light source. This can even kill the plant if you don’t do something about it as soon as you notice it. When you do, all you have to do is to reduce the exposure of the plant and leave it in a dark place to rest and consume energy. After this, it will be healthy again.


Do you have any other question about this subject? Which grow light is your favourite to use? Feel free to comment!

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  1. Thank you. This has been a huge help. I just bought my first grow light for a tomato plant that survived a drowning from a burst soaker hose. Surprisingly, after thinking it was dead it exhibited a trace of new growth. By summer’s end it appeared healthy. Our Alaska summers are short so what to do but bring tomato inside and shop for a grow light. I thought of leaving the light on all night on this, the first night, but fortunately found your article and now the light is off. I will start a schedule tomorrow and hope for success. Many thanks!!

    1. Hey Helen!

      Thank you very much for the kind words! I’m so happy this helped you out. Well, right, Alaska just calls for a good grow light. Which one did you choose? I have rewieved some of the best on amazon, so if you should need that info anytime in the near future, check it out. Fingers crossed! 🙂

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