Is Sunlight Bad For Betta Fish? – Should You Rely On It?

A healthy betta is one with rhythm. Bettas loves knowing the difference between day and night. that’s why all aquarists put so much effort into choosing the right light set-up for these fairy fish. But do you ever wonder whether sunlight works the same way as artificial light?

Bettas don’t benefit too much from sunlight. They are fine as long as the tank is bright enough for them to swim around and locate food. Since sunlight comes with high temperatures, it can disrupt the ideal water parameter you have set for the bettas.

Just because sunlight is natural doesn’t mean it is completely safe. In this article, we will talk about the good and bad sides of letting sunlight in your betta-tank. Then, you be the judge of whether you need it or not.

Key Takeaways

  • Sunlight is not something mandatory for a Betta’s growth.
  • Sunlight has enough brightness to light up a 50 to 75-gallon tank.
  • The warm color tone helps imitate Betta’s natural habitat.
  • The bright mid-day sunlight can contain more than 32,000 lumens.
  • Sunlight has a temperature which can lead to sunburn.

Is Sunlight Bright Enough For Betta Fish?

The only source of light a wild betta ever sees is sunlight. So to speak, sunlight should be enough for bettas swimming in your tank. But the problem is that wild bettas hardly receive direct sunlight. They hide themselves under dry & fallen leaves when the sun is too high. But your pets don’t have that privilege if the tank doesn’t have any hiding spot.

That’s why experts give mixed answers when asked whether sunlight is okay for a betta tank or not. But we will analyze the brightness level for now. The side effects are discussed later in this article.

The ideal brightness is 25 lumens per liter of water. But that works if the tank doesn’t have any type of live plants. If it does, you have to go beyond that limit. For low-demanding plants like Amazon Sword, 40 lumens per liter would be fine. In contrast, some high-demanding plants might require up to 70 lumens per liter.

For now, let’s assume you only own low-demanding plants. Here’s the approximate brightness level required for different tank sizes.

Tank Size in GallonTank Size in LiterLux/lumen needed
42159(159×40) = 6360

We have multiplied 40 (lumen per liter) with the tank size. It gives us the total number of lumens required to brighten up the tank adequately. We could have used 20 instead of 40 if the tank was a fish-only. However, the main reason why aquarists want sunlight is to help the photosynthesis process of aquatic plants.

So, we automatically assume bettas are not the only inhabitants of your tank. If your Tank doesn’t contain any sort of plant (even moss balls), you can replace the “40” with 20 or 25. The rest would be the same. You now know how much illumination your Betta tank needs. But do you know how bright sunlight can be? Well, there are multiple answers to this question.

See also  Do Bettas Need Filter? [Or Not?]

It’s because the sun’s brightness varies depending on the specific time of the day. The sun is cool and dimmed in the early morning. But as the day starts progressing, so does the brightness level. At high noon, you can barely look at the sun without squinting. Check out the table below to find out how the range of brightness differs from one part to another part of the day.

Time of the dayApproximate Lumens/Lux
Overcast day1000
8 am to 10 am10,000-25,000
High noon32000+

Well, you get basically every type of lighting from dimmed and warm to harsh. Considering our previous calculation, you can choose any particular time to let the natural light enter the fish tank. For example, suppose the tank is 50 gallons. That means, to get enough brightness in each liter of the tank, the light should have at least 7560 lumens. Now, match this requirement with table number 2. Do you find anything suitable?

We think the early morning period (from 8 am to 10 am) has enough sunlight to fulfill your needs. The same goes for tank sizes larger than 50 gallons. So, yeah, as far as the “brightness level” is concerned, sunlight doesn’t fall short.

Can You Put A 2-Gallon Betta Tank Under Direct Sunlight?

We don’t think it’s a good idea. A 2-gallon or 6-liter (approximately) tank needs only 240 to 250 lumens in total. Even if you want to keep the plants happy as well, you don’t need more than 300 lumens. The early sunrise might have enough brightness for such a small tank (400 lumens).

But as the day progresses, the brightness can go way beyond your maximum limit. Bright mid-noon sunlight containing 10,000 lumens will be blinding for a betta living in a 2-gallon tank.

How Does Sunlight Benefit A Betta-Tank?

Sunlight doesn’t benefit fish (Betta) as much as it does humans. Bettas don’t seem to care much about the light source. But there are certain ways sunlight boosts the overall water condition in your betta-tank. Let’s see.

1. Helps With Photosynthesis

Sunlight helps with the growth of your aquatic plants. Yes, artificial lights do a good job as well. But nothing can match sunlight’s wavelength, color temperature, or the abundance of photons. Even though betta fish hardly cares whether the light source is LED or natural, the aquatic herbs sure do.

You will see immense growth in plants within a few days of putting them under sunlight. No need to spend money on ammonia-free fertilizers.

2. Appropriate For High-Demanding Plants

High-demanding plants can be tough to grow inside an aquarium. Most of the time, you can’t put any substance in the water without considering its effects on the fish. So, you have very little control in your hand. It’s true for lighting as well. Some plants, including aquarium mosaic lilies, dwarf lilies, giant hair grass, stem plants, red tiger lotus, etc., are extremely needy. Their need for light surpasses your Betta and other fish in the tank.

So, it will be tough to find an LED light that can meet both kinds of needs. Sunlight can be your savior in this situation. The light has different intensities throughout the day. That way, both the plants and the fish get to be happy for some time throughout the day. Even if the sunlight gets brighter, your Betta fish can always find a plant to hide behind. That’s exactly what they do in the wild.

See also  35 Inspiring Planted Betta Tank Aquascaping Ideas [Underwater Paradise]

3. Gives A Natural Vibe

Who doesn’t want to replicate a natural inhabitant for their pets. That’s where the concept for a reef aquarium or planted aquarium originally came from. But, a wrong light set-up can ruin all your efforts. Imagine using a blue light on the aquarium. It wouldn’t make the fish feel at home in any sense. Natural light tends to be warmer in tone. That’s what the fish are used to.

So, if your aim is to make the Betta feel at home, try using the same light source as their home. After that, just decorate the tank with enough plants, granules, and sand. Your betta will thrive for sure.

gorgeous colorful betta fish
owner: Gabrielle Perry

4. Sterilizes The Water

We have kept the most important aspect of sunlight for the last. The UV ray found in sunlight has the power to sterilize the green aquarium water. By “green,” we mean water that is filled with microorganisms, harmful algae, and other parasites. The problem is you hardly see those tiny beings in the water.

The fish feels the change in water and starts to get extremely uncomfortable. Some bettas even get sick and infected due to all the germs lurking in the aquarium. Sometimes, even having a filter doesn’t help. That’s when you have to turn towards the sunlight. Keep the aquarium under direct sunlight for a while. The UV ray will slowly sterilize the water for you. all the germs and harmful bacteria will be dead within hours.

Does Sunlight Has No Risk At All For Betta Tank?

Sunlight is good, but it surely has its own defects. We highly prefer you take a look at the risks before using it for your Bettas.

1. High Temperature During Summer

Reportedly, the summer sun can reach a temperature of 80 to 90 degrees Fahrenheit. It can go up to 96 degrees Fahrenheit in the Middle East. The problem is both the sunlight and its heat are in a package. You can’t get rid of only one. That’s why experts don’t suggest putting aquariums under direct sunlight at noon.

It will increase the water temperature as well. The ideal range of temperature is usually 72 to 75 degrees Fahrenheit. As you can see, the sunlight is way hotter than your ideal temperature range. Living in high temperature water can cause stress, lack of hunger, lethargic behavior and so on.

2. Too Bright For A Betta-Only Tank

If you checked the range of brightness (in table 2), you know what we are talking about. Let’s take the morning into consideration. The brightness level can go from 10,000 to 25,000 lux. Imagine if you have a mid-size tank that requires not more than 10,000 lumens. What would you do if the sun shone brighter?

If the sunlight contains 25,000 lux, that would go way beyond your needs. And “too much brightness” is the major reason behind a betta’s frenetic or abnormal behavior. It doesn’t sleep or eat well. The fish is always triggered and alarmed. You won’t ever see a calm betta inside a highly lit aquarium.

gorgeous pink betta fish
Owner: Marleen Stegemann

3. You Don’t Have Any Control

It’s the extension of what we have just said. With artificial lights, you can control the brightness.

See also  Proper Temperature Guide For New Betta Owners [SIMPLIFIED]

But you don’t have any control while using sunlight. How bright a day is going to be depends entirely on the weather and the specific place you live in. If it’s cloudy, you might not get more than 1000 lux even after 10 a.m. So, you can barely ensure a consistent brightness for your betta tank. The low-light situation is not as bad as the opposite. If it’s too bright (especially during noon), your fish health will deteriorate over time.

4. Betta Can Get Sunburn

The main reason why we suggest you never put a fish tank under direct sunlight is the risk of sunburn. As you know, the sunlight can heat up the water pretty quickly. At around 90 to 96 degrees, the water becomes risky to stay in. The fish will lose its color and become dull. And, eventually, the fish will suffocate to death.

5. Rapid Growth Of Plant

We earlier said how sunlight will boost your plant’s growth. But it might not be at a steady rate. Some plants grow like crazy in the presence of sunlight. Within a few days, the entire tank might be filled with algae, moss, and strange herbs. With too many plants, keeping the water parameters in check becomes hard. It looks more like an aquatic jungle than a clean fish tank. your betta definitely thinks the same, too.

What To Consider Before Putting A Betta Tank Under Sunlight?

If you are still adamant about using sunlight, we assume you have to be away for a while. It’s best to rely on the sun. It will make sure the natural rhythm of your betta doesn’t get ruined. In that case, here are a few things to consider.

First of all, check the weather forecast daily. If it’s a rainy season, assume the sky can be dark and cloudy. Only sunlight might not be enough if it’s a big tank. Try to set an artificial light that will activate automatically for 5 hours. Or, the weather can be too hot with bright & clear sky. Make sure you have curtains on every window of the room. That way, you can just pull the curtains down to limit the entry of natural light into the tank.

What Are Some Alternative Light Options?

Incandescent light bulb is a great alternative to natural light. It imitates the tone of the early morning pretty accurately. During sunrise, the color temperature reaches 4000k, which is the same for an incandescent bulb as well (4000k-5000k). So, you have got the brightness level right.

But the problem with incandescent light is its heat production. Unlike LED, such a light source transfers most of its energy into heat (almost 90%). That’s the same reason we have also warned you not to use sunlight. So, switching to compact incandescent light bulbs will not do you any good.

However, LED light is not as “hot” as incandescent bulbs. It produces some heat, too. But that’s minimal compared to the previous options. As far as color tone or brightness level is concerned, LED is more versatile. LED lights come with this switch that lets you set the tone from warm to cool. You can go from 2700k (like sunset) to 6500k (mid-day) instantly with one LED light. That’s a huge plus point, don’t you think?

Before You Leave!!

Thankfully, Bettas are not that fussy about light. You are good to go as long as you figure out how to circulate a circadian rhythm. Don’t worry. we won’t leave you hanging with that piece of information. Follow our article on “betta fish lighting cycle.”

Muntaseer Rahman

About Author

Hello, I’m Muntaseer Rahman, the owner of I’m passionate about aquarium pets like shrimps, snails, crabs, and crayfish. I’ve created this website to share my expertise and help you provide better care for these amazing pets.


This site is owned and operated by Muntaseer Rahman. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to This site also participates in other affiliate programs and is compensated for referring traffic and business to these companies.