Do Aquarium Plants Need Light?

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If you’ve ever had a house plant, you already know the basics. Plants need soil nutrients, CO2, and light to stay healthy.

These are the basics. But the addition of glass and aquarium water makes things a bit more complicated, especially in terms of light exposure.

If you’re confused about aquarium plants and light, you’re not alone! We all go through a learning curve when we set up our first planted aquarium.

Luckily, you won’t have to search far and wide for some answers.

I’ll cover all the basics you need in this article! We’ll go over the type of light, the ideal quantity and time of the exposure, and common signs of light deficiency in plants.

So, let’s get started!

How Much Light Do Aquarium Plants Need?

In general, aquarium plants need 15-50 lumens per liter. A lumen is a unit of measurement for the total quantity of visible light emitted by a light source; 15 lumens per liter is the equivalent of 0.25 watts per liter.

Notice it’s quite a wide range.

The exact answer will depend on the type of plant you have.

Overall, we can classify aquarium plants into three categories— low, medium, and high-light plants:

– Low-light aquarium plants

They require the least light exposure, roughly 15-25 lumens or 0.25-0.40 watts per liter.

Low-light species include Java Moss, Java Fern, Hornwort, Brazilian Pennywort, Guppy Grass, certain Hygros, certain Crypts, Duckweed, and Water Wisteria.

– Medium-light aquarium plants

These plants require roughly 25-45 lumens or 0.40-0.75 watts per liter.

There’s some overlap between low and medium-light plants, as most plants can tolerate wide ranges of light exposure.

You’ll often see species listed as having “low-medium light needs” for this reason.

Popular species include Moneywort, Parrot’s Feather, Red Ludwigia, Rotala Rotundifolia, Waterwheel, and Crypt Spiralis.

– High-light plants

They need roughly 50-60 lumens or 0.8-1.0 watts per liter.

Most high-light plants can tolerate a wide range of light exposure, surviving in low to high-light settings.

Such plants include Peacock Moss, Anubias Nana, Amazon Frogbit, Pellia Moss, Pygmy Chain Sword, and Staurogyne Repens.

What Type of Light Is Best for Aquarium Plants?

In theory, you can choose between multiple methods to light your aquarium. You have natural sunlight, Ambiental light, incandescent bulbs, fluorescent bulbs, and LED lights.

Out of all these methods, LEDs are unbeatable, and for multiple good reasons:

– They’re energy and cost-efficient

LEDs use diodes to emit light. This makes them highly efficient when compared to both incandescent and fluorescent bulbs.

You’ll use 75% less energy than when using other lighting methods. This leads to lower costs, especially if the light has to stay on for up to 12 hours a day.

On top of that, LEDs also have a longer lifespan, so they need less frequent replacements. It’s a win-win situation!

– You get a lot of variety

LEDs are versatile. You can easily find a product with the exact light intensity and color range you need. This is important because the color range matters for more than just aesthetics.

In the simplest terms, you can choose between warm and cool light. Warm light has a longer wavelength and doesn’t penetrate as deeply as cool light.

Cool light has a shorter wavelength, so it can travel further throughout the aquarium.

If you have a very tall tank, cooler light might be a better choice for you. If you have floating plants, warmer light will be gentler.

– They don’t produce as much heat as other methods

LEDs are energy-efficient. They consume less than other lightbulbs. And the energy they do consume is used more efficiently.

As a result, you get less energy being lost as residual heat. This is great because aquariums are susceptible to overheating.

Whether placed under direct sunlight or a lightbulb, the aquarium glass is going to heat up quickly.

This will warm up the aquarium water, while also trapping the excess heat inside, creating a greenhouse effect.

This can harm both the plants and the fish in the tank. It’s not something you want. Luckily, it’s also easily avoidable if you choose LED lights over other sources.

How Long Should I Leave the Light on for My Aquarium Plants?

As a general rule, all aquarium plants need 8-12 hours of light exposure per day. Plants with low light requirements will thrive with just 8-10 hours of light.

Plants with higher light requirements will need closer to 12 hours of exposure.

The ideal range will depend on the light intensity, the type of plants you keep, and other factors such as Ambiental light.

For example, if you have medium-light plants, you can keep the lights on for 8-10 hours if the intensity is high.

Alternatively, if you have a low-intensity lightbulb, you can keep the lights on for 2 extra hours.

If you keep your aquarium in a bright or well-lit room, you can also turn off the artificial lights a little earlier. Remember, all light counts!

The light your aquarium receives from its surrounding will also contribute to the plant’s exposure. This brings me to another common question I get.

Can I Grow Aquarium Plants Without Light?

All light exposure counts, so, couldn’t just Ambiental light be enough to grow healthy plants? Sadly not!

Even if you have low-light plants in a well-lit room, it’s still advisable to keep the artificial lights on for at least 6 hours a day.

Besides, Ambiental light comes with many disadvantages when compared to LEDs.

Here are all the reasons why it’s a bad idea to keep aquarium plants without artificial lights:

– Room lighting won’t provide enough lumens for most plant species

The room light is spread over a wide area. It’s not directly targeted toward the aquarium. The further the light source, the lower the intensity and its effects.

– Sunlight exposure leads to overheating

Sunlight comes not with just visible light, but also UVA and UVB rays. These can raise the water temperature drastically and cause serious problems for your plants and fish.

– Sunlight exposure encourages algae bloom

Algae grow very quickly, especially when placed under direct light exposure. The other plants in your aquarium won’t stand a chance against these pesky algae.

– Ambiental light is unstable

You won’t get the same light intensity and duration of exposure every day. Some days are cloudy, some days are bright and hot.

With regards to room lighting, you’re probably not going to keep those on for 10 hours a day either.

What Happens If My Aquarium Plants Don’t Get Enough Light?

So, you need artificial lights for your planted aquarium. Otherwise, your plants won’t get enough light.

And if you’re thinking about using sunlight, the downsides outweigh the benefits. But what exactly happens when your plants don’t get enough light?

In short, insufficient light will lead to stunted and deformed growth at best, and the slow death of your aquarium plants at worst.

Here are just some of the symptoms of poor light exposure to get a better idea:

– Slow or inexistent growth

The plant can’t get generate enough energy to fuel itself, so it ceases to grow. This means the plants are getting just about enough light to stay alive.

– Plants grow tall but have a barren appearance

Good light exposure encourages wide, bushy growth with lots of leaves and stems. But if your plants don’t get enough light, they will put all their energy into growing taller, to reach more of that sweet, sweet light.

So, instead of growing lush and rich, the plants will look leggy with wide spaces between the stems and fewer leaves.

– Old leaves wither away and start falling off

If the light “deficiency” goes untreated for too long, the plant starts shedding its older leaves to conserve energy. You’ll see these effects in the leaves closest to the bottom of the aquarium.

These are the furthest away from the light. They serve no purpose because they can’t photosynthesize without light exposure.

Instead of spending extra energy to keep these leaves, the plant can save its resources by simply letting them die.

– Leaves become pale and discolored

Light is one of the main “nutrients” that plants use to create energy. Plants use chlorophyll, the green pigment in the leaves, to convert light into energy through a process called “photosynthesis”.

But it also goes the other way around. Plants also require light for chlorophyll formation. If the plant is light-deprived for long enough, new chlorophyll can’t be made.

The effects can be seen in young leaves, which appear pale green or pale yellow due to a decrease in pigments.

Conclusion

Like all other plants, aquarium plants need light to create energy. It’s a crucial nutrient. But the exact quantity depends on the species.

Low-light aquarium plants need as little as 15 lumens per liter. On the other end of the scale, high-light plants need 50 lumens and over.

There’s a lot of variation. But one thing remains true— absolutely no plant can survive without light. A light deficiency will quickly manifest through mild symptoms like stunted or deformed growth.

Over the long term, the old leaves will begin to fall off, while the plant loses its deep green pigmentation.

The best way to prevent this issue is by setting up your aquarium the right way. The best lighting method would be an LED lightbulb.

These come in a variety of outputs and colorations. Besides, LEDs are also energy and cost-efficient, and less likely to overheat your aquarium.

avatar I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.

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