Should I Turn Off The Grow Light At Night? (+Best Time To Run Them)

Grow lights have become immensely popular and helpful for indoor gardeners without access to plenty of natural sunlight. Many plant owners want to invest in them but do not know how to run them.

Most plants perform several developmental and restoration activities in the dark thus, it is recommended to switch off the grow light at night as plants need 8-10 hours of darkness after 14-16 hours of light. The best time to run those grow lights is during the day when the sun is up.

In this article, I will discuss more information regarding growing lights, how much time they should run, the correct ways to use them, and the best types of grow lights you should invest in. So let’s get started.

Artificial grow lights

For modern-day plant owners living in apartments and small spaces, finding out space with unlimited natural sunlight where they can keep their plants is difficult.

This is why artificial grow lights have become so popular today.

Though natural sunlight is the best for plants, those indoor plants which do not get the required sunlight live well under artificial grow light.

They provide support and control over the light requirements of the plants and are very helpful in areas or homes where sunlight is often insufficient due to seasons, the facing of the house, and so on.

Although these lights are very effective, you must know how to use them correctly.

Each plant has a different light requirement; thus, it is impossible to say how much light each needs.

Some do fine in low lights, while some needs full sunlight.

Light and darkness play an important role in the developmental process of the plant.

Like under light, plants carry on activities like photosynthesis; in darkness, the plants use that food to grow their roots and foliage. 

Also read: LED Vs. Fluorescent Grow Lights (Pros & Cons+Best Picks)

How much light does your plant needs?

Most indoor plants require sunlight between 12-16 hours per day.

Most plants we grow indoors belong to tropical regions where they are perennials.

Thus, they need longer day hours to grow to their best.

But to understand exactly how much light your plant needs, you need to know where they truly belong.

You have to understand how much light, and for long those regions receive.

Most tropical plants are warm weather-loving, so they need 12-16 hours of light to stay warm.

However, plants that are native to colder climates might be happy in lesser daylight hours.

What happens when the plants get too much light?

When the plant begins to get too much light and gets no darkness, the biological clock is confused and hampered.

The plant in full light cannot use the energy it stores inside because it needs darkness to perform it.

Leaving the grow lights on for a constantly long period without giving the plant darkness can result in some problems.

Too much light can stunt the plant’s growth, scorch the leaves of the plant, and cause wilting of the plants.

Too much light can also dry out the plant’s soil quickly, dehydrating the plants.

This might affect the growth of flowers and fruits in the plant.

Why do plants need darkness?

Let us briefly understand the work that plants do in darkness.

One very common mistake plant growers do keeping the lights on all day, every day.

While it may be a misconception that the lighter, the better the growth, it is not fully true because, as humans, plants also need a few hours of darkness to rest.

Darkness is a crucial time for the development of plants when they concentrate on root development and distribute the stored energy throughout the plant.

Running the grow lights all day and night can destroy the plant’s photoreceptor cell, which is responsible for performing all the important internal activities it performs at night.

Plants, just like humans, have a biological clock and perform activities as per the clock.

In the daylight, the chlorophyll of the plants absorbs the sunlight, which fuels the photosynthesis process and uses the water, and oxygen from the air to create starch and sugar.

The plant then stores these sugar and starch molecules for its development during the night.

During the darkness, the plant uses that starch to fuel its growth activities and transform them into energy for the plant to feed and run.

Thus we can understand how crucial darkness is to plants to fuel their developmental process.

Should I run my grow lights at night?

So many plant owners using grow lights might think that since light is good for plants, why not put the lights on for 24 hours straight without putting it off ever?

But the truth is that darkness, just as light, plays a crucial role in the life of plants.

It is not necessary to use the grow lights at night even though some plants need more light than others; the darkness period is crucial for plants to grow.

Let us glance through the light requirement of some plants:

Plants that need 6-8 hours of light	Plants that need 8-12 hours of light	Plants that need 14-18 hours of light
Basil Strawberry Thyme Rosemary Cherry tomatoes	Ferns Begonias African violets	Figs Lemon tree Large tomatoes Aloe vera Cucumbers Small orange tree

Also read: How To Use Grow Lights For Indoor Plants?

The best time of day for using grow lights

Though there is no hard and fast rule of exactly how many hours you should run the grow lights, keeping them on in the typical daylight hours, for example, 6 am to 10 pm, is recommended.

But some gardeners also keep their lights on through the evening and night.

You can choose the hours at your convenience but what is important is to be sure that you consistently maintain the same timings every day and maintain a schedule.

1. Using timers

The vital part is maintaining a consistent schedule to keep the grow light on.

If you find it difficult to maintain, you must invest in a timer.

They are not very expensive and work great, and are very effective. 

2. Running lights at night 

Many gardeners run their grow lights simultaneously for multiple reasons that suit their convenience.

Those gardeners, who live in extremely cold areas, keep the grow lights open because the nights are very cold, affecting the plant’s health.

So, to keep the plants warm in these areas, the grow lights are kept running.

Similarly, those living in very hot areas keep the grow lights on at night because the days are already so hot that keeping the lights on during the day can warm them more.

Some plant grower also keeps their grow lights n at night because the electricity costs are lower at night.

So you can choose the hours of grow lights as per your convenience, provided you maintain a consistent timing and ensure that your plants get at least 4-8 hours of darkness where they can rest.

If your plants are adjusted to a natural light cycle, and you need to acclimate them to a different light schedule, you need to bring the changes gradually.

Adjust the schedule by one hour every day instead of suddenly changing the schedule one fine day. 

How long does it take to run grow lights?

There is no fixed hour, but you can run the lights depending on the need of the plants.

You have to closely see the response of the plants to find out if it is happy with the light it is getting or whether it needs more light.

If you see signs of leaf burns or scorching in your plant, that is a sign that the plant is getting too much light, and in that case, you need to reduce it and move the plants further away from the light.

On the other hand, if the plant shows signs like droopy yellow leaves, and faded colors on the leaves, then it is a sign that the plant needs more light, so you need to increase the timings.

If the seedlings and leaves are growing upwards quickly, it is a clear sign that the plant is thriving, while if the plants are beginning to look leggy, they need more light.

Seed starting

If you are starting seedlings under the grow light, it needs a minimum of 12- 16 hours of light because they need more light than adult plants but be careful not to burn the delicate leaves with scorching light, so ensure some distance between the light and the seedlings.

If you use LED lights, hang the lights at least 2 feet away from the seedlings and as they grow, move the lights.

If you use fluorescent lights, hang them 4 inches-6 inches away from the seedlings and move them as the plants grow. 

Vegetative growth

Mature plants can grow in more light than seedlings and tolerate up to 14-18 hours of growth light daily.

Attach fluorescent bulbs about 12 inches away from the plants and the LEDs 1-2 feet away from the plant. 

How can I tell if my plants are thriving under grow lights?

Your plants will show signs of whether it needs more light or is getting too much light.

Here are some signs of an unhappy plant:

• Limp leaves
• Smaller leaf size
• Shriveled leaves
• Small and bitter fruits
• Yellowing or browning
• Thin and leggy plant
• Stunted growth

Try these solutions if the plants show the above signs:

• Check for pests and bugs.
• Feed the plants.
• Check for watering issues.
• Check the roots for signs of rotting. 
• Add more natural light or blue light to the plant.

Which color grow lights are best?

Grow lights are designed in a way that would imitate the natural sunlight. 

The sun looks yellow but is made up of a spectrum of colors.

Grow lights come in different colors and sizes, and you need to choose the ones suited best for you. 

• White LED: White LED is not just white as they look. They have all the necessary spectrums that plants need, so they are versatile and work well for fruits and vegetables. 
• Red light: These lights are ideal for flowering and fruit plants.
• Blue light: Blue lights are cool and focus on the plants’ green growth and are best for vegetables and herbs. 

Final words 

Grow lights are an immensely important discovery that gardeners have adopted and embraced worldwide. Once you know and learn the basics of using them correctly, you can start a flourishing greenhouse at your home.

Grow lights are best for plants that don’t get enough natural light already. However, they are not supposed to be used for 24 hours straight. You should turn them off at night and let your plants experience darkness because they also need that.

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Sources: University of Minnesota, David H. Trinklein, Horticulture State Specialist, The University of Georgia, The Royal Horticultural Society.