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Planted Tank: How Long You Should Leave the Light On

I’ve been trying to find the optimal balance in my planted tank for a long time now, and the right light duration is an important aspect. At the start, I was unsure how long I should keep my lights on, but after a couple of years I’m confident I can advice you on this matter.

Quick Answer

In a planted tank, the lights should be on between 8 to 10 hours. Too long will give algae the chance to start growing, so never turn your lights on for longer than 12 hours per day. In a new tank, start with 8 hours per day and adjust as necessary.

However, different plants have different requirements. The duration is also dependent on the type of light you have. Therefore, I’ll go over these topics briefly in this article.

Importance of Lighting Your Planted Tank Right

The lighting in your aquarium helps create visibility in your tank. It also makes your tank look more pleasing to the eye and regulates your fish’s sleep and wake cycle. However, lighting does not just help your fish.

As I mentioned before, lighting your planted tank is vital to your plant’s health. Without the right kind of tank lighting, your plants won’t survive underwater.

In fact, plants require certain amounts of light to live in your tank. As a result, you want to be careful about the amount of light exposure present in your aquarium.

How Long Can You Leave Your Tank Light on?

In truth, you don’t want to have your tank lights on for too long. Still, you should not deprive your plants of light either. Too little light will also cause plant deterioration and death. But, the amount of light that you add to a planted tank will depend on the plants you have.

I recommend turning the lights on for 8 hours per day in any new tank. After about a week you’ll be able to see if this is too much or too little, based on observations in your tank. If it’s too much light, green algae will start to grow. Often, this is hair algae or thread algae. If it’s not enough lights, your plants will not grow properly and sometimes brown algae will start to develop.

You have to know what your plant needs specifically to give it a healthy life. However, generally, plants will need anywhere from eight to ten hours of light to stay in good condition.

Any more than twelve hours of light could cause your plants to wilt or even die. So, keep this number in mind. You never want to leave your aquarium lights on all day either. Instead, you want to have your light on a timer to keep it active for a certain amount of hours. Alternatively, you can create a schedule for your plants and turn off the light manually.

Lighting Requirements For Popular Aquarium Plants:

I talked about the general amount of time plants need to be exposed to light. In this next section, though, I’ll get into more specific numbers.

I’ll discuss exactly how long you should leave your aquarium light on for certain plant types. This way you can optimize the amount of light you give your plant.

The type of aquarium plant you have will determine your tank’s light needs by and large. Each plant has different needs. In addition, the size of your plant can also play a role in your light needs so keep this in mind!

1. Carpet Plants

Carpet plants are a popular type of tank plants. They are usually quite difficult to care for and need medium to high levels of light to survive. Because of the high lighting requirements these plants can need up to 12 hours of light, but in most cases it’s better to increase the brightness of your lights.

Here are some popular carpet plants that have different lighting requirements. Use this information to get an idea or feeling about lighting requirements for carpet plants.

Baby Dwarf Tears:

Baby Dwarf Tears is one type of carpet plant you can try out in your tank. Dwarf Tears has a high light requirement and can be placed in both large and small tanks. Around ten to twelve hours of light is ideal for this plant.

Java Moss:

Java Moss is another popular carpet plant and can thrive in low-level light. But, you want to be careful with this plant. It can be hard to manage if you haven’t dealt with carpet plants before in a tank. Anywhere from eight to ten hours of light will help this plant thrive.


Finally, you can also get Lilaeopsis for your planted aquarium. This plant won’t need a full twelve hours of light. But, it does grow quite rapidly. I recommend using a timed light for this carpet plant. Nine to ten hours of light will be good for this plant type!

2. Mid-Ground Plants

Mid-Ground Plants can also be purchased for your planted aquarium. These types of plants are a little more manageable than carpet plants. And, usually, they only need around eight hours of light.

You won’t have to do much with these plants either. So, this can be a plus for aquarium beginners.

Pygmy Chain Sword:

This plant type looks like grass and is one of the easiest plants to keep track of in a tank. It grows well with medium light. But it can even grow with high light exposure.

And, you won’t have to worry about upkeep too much with this plant. You can give up to 12 hours of light to the Chain Sword.

Anubias Nana:

The Anubias Nana is a variant of the Anubias Barteri. It is smaller than the Barteri, though, and it does not require much light to live in your tank. So, this is another great choice for planted tanks.

Especially if you want something with less intense lighting needs! Around eight to nine hours is a good amount of light for this plant. 

3. Background Plants

Background plants are the final plant type I will be discussing in this post. There are plenty of great background plants to choose from. And, these types of flora are perfect if you want to make your tank look more full and appealing.

The lighting needs of background plants will differ between species, though. So you want to know the specific requirements of any plant you get. I’ll talk about a few of the most popular background plants here to get you started.

Amazon Sword:

Amazon Sword will need under 10 hours of light. This is another easy to manage plant that has low light requirements. But, it can also thrive in medium levels of light.

In addition, you won’t need an expensive lighting device to keep this plant growing. It lengthens with very little light and care.

African Water Fern:

African Water Fern is great for new tank owners, as well. This plant will need more light than an Amazon Sword. Around twelve hours of light is needed for the Water Fern.


Pondweed is the final plant I will talk about in this article. It can grow in a variety of environments. And, it can handle all kinds of lighting. You can use less or more light depending on how you want this plant to grow.

More light will make Pondweed grow taller and fuller. Less light will keep this plant smaller and more manageable.

What Kind of Lights Should I Get For My Planted Tank?

Aquarium lights come in a ton of different varieties. You can choose from different bulb types, power outputs, and even colors. The choice is up to you, but you do want to consider your plant, as well. Certain light intensity will be better or worse for your tank plants.

For instance, one type of lighting option you can go with is fluorescent lights. Fluorescents tend to give off more intense light. So, you won’t have to install as many fluorescent bulbs in your tank.

However, LED is another popular option you could go with. These types of light are more cost-effective and can be quite powerful. But, you might have to put more of these types of bulbs into your tank if your plant has high lighting needs.

Ultimately, the type of light you get is up to you. Really, the most important factor to consider is your plant’s care needs!

How Should I Light My Planted Aquarium While I’m on Vacation?

When you go away on vacation, your planted aquarium will still need light. You could have someone check in on your aquarium and turn off your tank light at night. But, this could be a major hassle.

Really, I would recommend getting a timed light for your tank. Timed lights can be more expensive depending on which device you get. Still, these types of tank lights are convenient and dependable. You won’t have to worry about your tank lighting while you are away!

The truth is that any type of light can be automatically turned on and off if you use a timer. A timer, for example this one on Amazon, can be plugged in your power outlet. You can program it exactly the way you want. If you don’t have one yet I really recommend you getting one online or at a local hardware store.

And, timed lights can also be used on a regular basis. This way your tank has a regular light schedule. You might be wondering whether you should leave your tank light on at night.

You could do this. But, it is better to keep your lights on in the daylight and turn them off at night. This will help promote fish and plant health!