Updated at: 21-11-2022 - By: Sienna Lewis

People who don’t have access to an outdoor garden may find that using a grow light is a wonderful alternative. You can still get the rewards of raising your own fruits, veggies, and flowers. To maximize your chances of success, you must decide how long to leave grow lights on.

Grow lights should be on for 12 to 18 hours a day for most plants. However, the length of time varies widely based on the plant’s tolerance for shade and the amount of light it receives from the grow light (light intensity, light quality, distance from plant). Some grow lights may need to be on for as many as 22 hours every day.

Even if you’re an experienced gardener, utilizing a grow light can be intimidating if you’re new to the hobby. You can develop a garden indoors just as easily with the help of this fantastic equipment. Continue reading to find out more about the different types of growing light schedules available.

How Long Should You Leave Grow Lights On?

Regardless of what you choose to plant, you should think about how long you want to leave a plant light on for each one. A grow light should be left on for at least half of the day, or between 12 and 14 hours, for most plants.

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There are a wide range of grow lights available, and each one has its own unique set of specifications for light intensity and quality.

Some grow lights can be left on longer, such as low- and medium-intensity lights, while others can be left on for about 10-14 hours a day.

A number of factors influence how long you should leave a grow light on.

To begin, consider how much light the plant requires. The amount of light required by spinach and other leafy greens is smaller than that required by flowers, for example.

The area around the light sources should also be taken into account. Using a grow light for a shorter period of time is possible if you have a nearby window or a huge artificial light source.

The plant’s age should also be taken into consideration. Seedlings require a lot more light than mature plants because they are still developing. In order to see how they stack up, compare them.

How many hours of light do seedlings need?

Most seedlings require between 14 and 18 hours of sunshine every day for growth, depending on the type of plant.

Since most seeds don’t need light to germinate, this is a departure from starting seeds.

Begonia, Primula, Coleus, and other common seedlings require light to germinate.

Seedlings, on the other hand, typically require 16 hours of light every day to thrive. However, the amount of light needed will depend on the following factors:

  • The plant’s tolerance for shade
  • The brightness of the illumination
  • Quality of light, as measured by its hues and wavelengths

A tomato plant might obtain adequate light in the summer with only 5 hours of direct sunlight, but it would need 22 hours of light from a dim fluorescent light.

How Long Should Grow Lights Be On for Seedlings?

How many hours of light do seedlings require when they first arrive?

Seedlings, in general, need more light than mature plants, unless you’re growing veggies that yield fruit.

In order to assist the seedlings grow, it is imperative that they receive the additional light immediately.

A lack of watering could stunt the growth of the plants. The plant’s health will suffer if the leaves turn yellow or pale.

Plant stems become lengthy and “leggy” as a result of limited light.

It is the plant’s attempt to increase the amount of light it receives that causes it to grow taller stems.

It is recommended that your seedlings receive light for 16 to 18 hours a day, but you can obtain as much as 20-22 hours if you use a low- or medium-intensity grow lamp.

It’s a good rule of thumb to keep the lights on for 16 to 18 hours per day. The length of time that seedlings should be exposed to grow lights will vary substantially, mostly because of:

  • The amount of light that is emitted
  • Light’s characteristics (such as color and wavelengths)
  • The amount of light that a particular plant species needs (i.e., low-light plants require less light than full-sun plant varieties)

If you’d want to boost the brightness of your grow light, you may just move it closer to your plants.

How Long Should Grow Lights Be On for Older Plants?

You won’t need to use the grow light as much after your plants have grown to their full potential.

Because they’ve stopped developing, a grow light is necessary. However, you should not completely give up your grow light.

Even when fully developed, plants require a minimum of 12 to 14 hours of daily light to thrive.

If your plants are near a window, you may be able to reduce the amount of light they receive. If you use an overhead artificial light for most of the day, you’ll get the same effect.

Grow Light Schedule for Vegetables

For vegetables and other plants, a light schedule is important. Make sure to turn on the LED light every day so you don’t miss it.

Setting an alarm may be necessary at first to remind you. Turning the light on and off will become second nature to you with time.

Consider a few variables that could change your schedule when you grow a light one.

Try a few simple schedules to see what works best for you. Here are some suggestions to get you started.

Grow light hours per day for vegetables

Set a routine that you can follow to for the plant or plants that you are caring for.

Suppose you need to use the light for 16 hours and sleep for 8 hours. You can switch the light on when you wake up and off when you go to sleep.

Set a timer to turn the lights on and off at certain times of the day if that’s all you require.

In either case, it’s critical that you maintain a regular routine for your plants so that they can thrive.

When to use grow lights for vegetables

Try to keep the grow light on for as long as possible during the day rather than just at night.

That manner, the effects of the grow light can imitate those of the sun, allowing your plants to grow as if they were outside.

While the grow light can be used at night, any natural or artificial light may interfere during the day..

It’s best to keep your grow light in sync with the natural light unless your space has no windows.

How long to leave plant light on

The first step is to determine how long to leave the grow lights on.

Consider the age of your plants, as well as the health of your pets. Determine the time of day you intend to switch on the lights.

When it comes to most types of plants, the amount of light they need is between 12 and 18 hours a day.

Instead of using the grow light, you can leave it off when your plants are exposed to natural light, such as through a window.

Tomatoes, cucumbers, and strawberries, for example, require about 16-18 hours of sunshine to mature.

Here is a complete article about growing veggies using grow lights, if you want more information.

Plants should receive the same amount of sunshine as they would if they were growing outdoors in summer by using grow light intensity, color, and duration.

You can figure out when it’s time to turn out the lights by adding up the number of hours in a day. There is no need to keep track of the exact number of hours.

The optimal schedule for your plants’ growth must be kept as close to reality as feasible.

What Can Affect the Grow Light Schedule

Your grow light schedule can be affected or justified by a number of factors.

When growing plants, it’s best to maintain as comparable of an environment as possible. That way, you’ll be able to see how it works in practice.

How Long Should You Leave Grow Lights On For? | Urban Leaf

Some things to keep in mind when you plan your grow light schedule:

  • Light wattage
  • Distance from the light source (i.e. less strong light is received by a plant that is further away from a light source)
  • Colors and wavelengths of light (i.e., light quality)
  • Duration that isn’t too long

Light Intensity

To begin, consider the intensity of the lighting.

Grow lights are available in low, medium, and high intensity.

Higher intensity lights require less power to produce the same effects as lower or medium intensity lights.

Some plants, on the other hand, necessitate a high level of intensity regardless of the circumstances.

That much light is too much for some plants, who require lower conditions.

If you have a lot of plants, you may want to think about how much light they need.

Light Color

Consider the color of your grow light, as well as the intensity of the light.

You don’t need to go for a different light because white grow lights are suitable for a wide range of plants.

Blue or mixed lights are good for seedlings since they promote growth.

However, as your plant grows, you may want to consider using a red light instead.

Indoors, red grow lights can help prevent plants from growing to unmanageable heights. They can also aid in the development of buds in blooming plants, allowing them to produce nectar and pollen.

There’s still a lot to learn about plant growth in relation to light hue and quality.

For your convenience, we’ve written a comprehensive article on how light color impacts plant growth.

Light Distance

You may also wish to reposition the lights and vary the schedule of your grow lights.

Four to six inches of light is ideal for seedlings.

When the plants get taller, you’ll need to adjust the light up so that they don’t strike it.

When it comes to lettuce, herbs, and other flowering houseplants, you’ll need around 6 to 12 inches between them and the light source.

Foliage houseplants, on the other hand, require a minimum of 12 to 24 inches of clearance.

Adjusting the position of the light and reducing the light hours may be necessary as your plants grow.

If you’re interested in learning more about how far away LED lights should be from plants, check out our in-depth article.

Plant Type and Age

What kind of plant you have and how old it is the final consideration. Seedlings, as previously said, require more light than mature plants.

Gardening experts can help you figure out how much light your plants need. There is no risk of over or under-lighting the plants this way.

Step 1 – Understand The ‘Ideal’ Hours Of Light Per Day For Your Plants

Short Vs Long Day Plants – How Their Light Needs Differ

When it comes to plants, scientists categorize them into “long” and “short” day plants.

  • To flower, LONG-DAY plants require only brief periods of darkness. Basil, cilantro, parsley, dill, mint, and tomatoes are all examples of LONG day plants.
  • Conversely, short-day plants demand long periods of darkness in order to bloom. Avocados, mustard greens, marigolds, zinnias, and strawberries are all examples of SHORT-DAY plants.

If you wanted to mimic the perfect growing conditions of a plant, all you’d have to do is seek up the ideal day length and use it to program your grow light’s on/off timer.

The drawback with this strategy is that your plants are more likely to blossom fast if you take it. Flowering can be a wonderful thing for certain plants (like tomatoes and peppers), but for others (like lettuce and cilantro), it’s the beginning of the end. As the leaves change shape, their flavor might turn unpleasant, and most gardeners will just remove them and start over.

We can also categorise plants based on whether or not they prefer to flower, or if they prefer not to flower.

Using Light Duration To Promote (Or Avoid) Flowering

So, if you want your plants to flower, make sure you provide them with the right amount of light for the right amount of time. If flowering is unwanted in a plant, the inverse should be done. At this point, we find it useful to divide the plant world into four sections.

  • Fig
  • Peach
  • Tomato
  • Avocado
  • Chamomile
  • Coffee
  • Cosmos
  • Marigold
  • Strawberry
  • Zinnia
  • Arugula
  • Basil
  • Cilantro
  • Dill
  • Balm of Lime
  • Lettuce
  • Mint
  • Parsley
  • Ginger
  • Sage

Is There A Limit To How Long You Can Leave Lights On For?

Yes, in a nutshell. Even in environments where flowering is a desirable trait, long-day plants have a finite lifespan. ‘Plants Do Math At Night’ explains this. Seedlings need at least 6 hours of daily respiration, and more developed plants need 8-10 hours or more. How Long Should You Let Them Sleep? When cultivating long-day-loving types and attempting to promote flowering/fruit from them, we do not advocate providing more than 14-16 hours of light every day.

Step 2 – Understand The ‘Ideal’ Daily Light Integral (DLI) Requirements For Your Plants

It isn’t just the amount of light that plants need each day that varies; they also have variable needs in terms of the amount of time they spend in the sun. The term “Daily Light Integral” or DLI is used to measure this “volume” of light. Check out ‘Grow Lights For Indoor Plants–How To Measure It, and Understanding Watts, PPF, PPFD and DLI’ if you want to learn more about this topic.

DLI of 1-4 mol/m2/day may be sufficient for decorative indoor plants like pothos, snake plants, or monstera, but most edible plants will require a DLI of 10-30 mol/m2/day.

If you’re curious about how much light energy falls on an object (say, a plant leaf) over the course of 24 hours (DLI), here’s an explanation: A plant’s daily calorie intake (DLI) is different from that of a human because each plant has its own unique needs. If you don’t provide enough DLI to a plant for a lengthy period of time, it’s the same as not providing enough calories to you. You may, at worst, become irritable due to hunger. You could die, if the worst happens.

Step 3 – Calculate The Ideal Light Intensity (PPFD) Requirements For Your Plants

To determine the appropriate light supply rate, we simply divide the ideal time/duration by the total volume of light required by the plant. To put it another way, this is the same logic you’d apply if I told you we had a 10-gallon bucket and needed to fill it over the course of five hours. Just divide 10 by 5 to get 2 gallons per hour for the bucket’s fill rate.

When it comes to water flow, we measure it in gallons per hour, but when it comes to light flow, we measure it in moles per square meter per second, or mol/m2/s.

In the following table, we’ve summarized this math for you. In the event that you have questions about a plant that isn’t on this list, feel free to post a comment and we’ll try our best to answer them.

Other Considerations In Determining How Many Hours A Day Are Needed For Indoor Plant Grow Lights

When deciding how long to leave your grow lights on for indoor plants, there are a few more things to consider:

  • A high rate of flow is required to meet the goal DLI in a short period of time (PPFD). Plants can also get ‘light burned’, much like humans can get sunburned. Excessive exposure to PPFD will most likely result in browning of plant leaves.
  • To encourage a plant to flower, gradually increase the amount of time it spends in the sun. Plants can be tricked into thinking that the growing season is coming to an end by gradually reducing the length of the day. Prior to that happening, they’ll be looking to get their fruit in the ground.
  • Plants need slumber, too. At night, they carry out vital respiratory activities. Seedlings need at least six hours of darkness a day, whereas mature plants need at least eight to ten hours of darkness each day.

Thanks for reading our indoor edible gardening and grow light guide; we hope you found it informative. Now that you know what an optimal PPFD is, you can use that information to determine where and what kind of grow light you require. You can learn more about this topic by reading ‘Setup and Placement of Grow Lights For Plants – How To Get The Distance Right?’ (coming soon) and by joining up for our email list below (which will be available shortly).

How Many Watts Per Plant For Led Grow Lights - Grower Today

We hope you found this information about grow lights and indoor edible gardening to be helpful. The next obvious step is to apply what you’ve learned about the perfect PPFD to figuring out where and what kind of grow light you’ll need to get started. Our upcoming article, ‘How To Get The Distance Right?’ on setting up and placing grow lights for plants, as well as signing up for our email list, are excellent resources for those interested in learning more.

Final Thoughts

Grow lights should be left on for 12 to 18 hours a day at the very least. The actual timetable is influenced by a variety of things. When planning a growing timetable for veggies and other plants, be sure to take into account all of them.